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HAND-BOOK 


OF 


PHYSIOLOGY 


' 


BLDDD-5PECTRA  CDMPAREO  WITH  SPECTRUM  DF  ARGAND-  LAMP 


1  Spectrum  oF  Argand-lamp  with  FraunhDFers  linES  in  position. 

2  Spectmm  dP"  DxyhsOTnglobin  in  diluted  blaad. 

3  Spectrum  oF  Reduced  rfaama^lnbin 

4  Spectrum  or  Carbonic  oxide  Haemoglobin. 

5  Spectrum  oP  AcidHaama+m  in  ethenal  solution. 

6  Spectrum  oP  Alkaline  Haamatm. 

7  Spectrum  oF  CbiaroFnrm  extract  dF  acidulated  Dx-Bile. 

8  Spectrum  oF  MethaBmo^lobin. 

9  Spectrom  oF  HsmDchrDrnDi^En. 
10  Spectrum  oF  Haematoporphynn. 

Most  of  the  above  Spectra  funv  been  drawn  from  obsen'ations  by  MTWlepruik  ECS'. 


SAGKErTfttflLHELHS  LI 


KIRKES'  HANDBOOK 


OF 


PHYSIOLOGY 


Revised  and    Rewritten  by 

CHARLES  WILSON   GREENE,  A.M.,  Ph.D 

Professor  of  Physiology  and  Pharmacology 
University  of  Missouri 


Stxtb  Bmevtcan  iRevfsion 


WITH  FIVE  HUNDRED  AND  SEVEN  ILLUSTRATIONS, 
INCLUDING  MANY  IN  COLORS 


NEW    YORK 

WILLIAM   WOOD   AND   COMPANY 

MDCCCCVII 


a' 


Copyright,   1907 
By  WILLIAM  WOOD  AND  COMPANY 


PREFATORY    NOTE 

The  general  organization  of  the  Handbook  has  been  retained  in 
the  present  revision,  but  the  anatomical  discussions  have  been  very 
greatly  reduced.  The  text  has  been  largely  rewritten  throughout,  and 
many  new  illustrations  of  physiological  experiments  have  been  intro- 
duced. An  entirely  new  feature  is  the  introduction,  at  the  end  of  the 
chapters,  of  directions  for  laboratory  work.  It  is  hoped  that  this  will 
greatly  increase  the  utility  of  the  book  both  to  the  teacher  and  to  the 
student.  Acknowledgment  is  given  my  colleagues,  Dr.  C.  M.  Jack- 
son for  reading  the  manuscript  on  the  Nervous  System,  and  Miss 
Caroline  McGill  for  similar  criticism  of  the  chapter  on  the  Elementary 

Structure  of  the  Tissues. 

CHAS.  W.  GREENE. 

Columbia,  Missouri,  October  1,   1907. 


CONTENTS 


PAGE 

CHAPTER  I — The  Phenomena  of  Life;    Properties  of  Protoplasm,       i 
Structure  of  Protoplasm,  ......... 

CHAPTER  II — Cell  Differentiation  and  the  Structure  of  the 
Elementary  Tissues;  The  Structure  of  the  Cell,  The  Structure  of 
the  Elementary  Tissues.  I.  The  Epithelial  Tissues.  II.  The  Con- 
nective   Tissues.     III.  Muscular   Tissue.     IV.  Nervous   Tissue,    .     17 

CHAPTER  III — The  Chemical  Composition  of  the  Body;  The 
Nitrogenous  Bodies,  Classes  of  Proteids,  Oils  and  Fats,  Carbohy- 
drates,  Inorganic  Principles,  Laboratory  Experiments,  .         .         -78 

CHAPTER  IV— The  Blood;  Quantity  of  the  Blood,  Coagulation  of  the 
Blood,  Morphology  of  the  Blood,  Chemical  Composition  of  the  Blood, 
Globulocidal  and  Other  Properties  of  Serum,  The  Character  and 
Composition  of  Lymph,  Laboratory  Experiments,  ....  101 

CHAPTER  V — The  Circulation  of  the  Blood;  Anatomical  Con- 
siderations, The  Action  of  the  Heart,  The  Regulative  Influence  of  the 
Central  Nervous  System,  The  Circulation  through  the  Blood-Ves- 
sels,  The  Pulse,  The  Peripheral  Regulation  of  the  Flow  of  Blood, 
Vaso-constrictor  and  Vaso-dilator  Nerves  for  Individual  Organs, 
Laboratory  Experiments,  .........  141 

CHAPTER  VI — Respiration;  The  Respiratory  Apparatus,  The  Move- 
ments of  the  Respiratory  Mechanism,  Respiratory  Changes  in  the  Air 
Breathed,  The  Respiratory  Changes  in  the  Blood,  The  Nervous 
Regulation  of  the  Respiratory  Apparatus,  The  Effect  of  Respira- 
tion on  the  Circulation,  Laboratory  Experiments  in  Respiration,      .  243 

CHAPTER  VII— Secretion  in  General;  Organs  and  Tissues  of  Secre- 
tion, Secreting  Glands,  The  Process  of  Secretion.  Influence  of  the 
Nervous  System  on  Secretion, 291 


VI  CONTENTS 

PAGE 

CHAPTER  VIII — Foob  and  Digestion;  Food  and  Food  Principles, 
The  Process  of  Digestion,  Digestion  in  the  Mouth,  Deglutition,  Ner- 
vous Mechanism  of  Deglutition,  Digestion  in  the  Stomach,  Move- 
ments of  the  Stomach,  Digestion  in  the  Intestines,  Movements  of 
the  Intestines,  Laboratory  Experiments  in  Digestion,  Saliva  and  Sali- 
vary Digestion,  Gastric  Juice  and  Gastric  Digestion,  Pancreatic  Juice 
and  Pancreatic  Digestion, 297 

CHAPTER  IX — Absorption;  Absorption  in  the  Stomach,  Absorption  in 

the  Intestines,  Absorption  from  the  Skin,  the  Lungs,  etc.,  .         .         -361 

CHAPTER  X — Excretion;  Structure  and  Function  of  the  Kidneys, 
General  Structure,  The  Urine,  The  Method  of  Excretion  of  Urine, 
The  Discharge  of  the  Urine,  The  Structure  and  Excretory  Func- 
tions of  the  Skin,  Laboratory  Experiments  in  Excretion,     .       .       -371 

CHAPTER  XI — Metabolism,  Nutrition,  and  Diet;  Metabolism  of 
Proteids,  The  Metabolism  of  Fats,  The  Metabolism  of  Carbohy- 
drates, Requisites  of  a  Normal  Diet,  The  Influence  of  the  Ductless 
Glands  on  Metabolism,  .........  405 

CHAPTER  XII — Animal  Heat;  Heat-producing  Organs,  Variation  in 
the  Loss  of  Heat,  Variation  in  the  Production  of  Heat,  Influence  of 
the  Nervous  System  on  Heat  Production, 433 

CHAPTER  XIII — Muscle-Nerve  Physiology;  Chemical  Composi- 
.  tion  of  Muscle,  The  Properties  of  Living  Muscle,  Single  Muscle  Con- 
tractions, Conditions  which  Affect  the  Irritability  of  the  Muscle  and 
the  Character  of  the  Contraction,  Tetanic  and  Voluntary  Muscular 
Contractions,  The  Type  of  Contraction  in  Involuntary  Muscle  and  in 
Cilia,  The  Function  of  Nerve  Fiber,  Some  Special  Coordinated  Motor 
Activities,  Locomotion,  The  Production  of  the  Voice,  Laboratory 
Experiments  on  Muscle  and  Nerves,         ......  440 

CHAPTER  XIV— The  Nervous  System;  I.  Function  of  the  Nerve 
Cell.  II.  The  Structure  and  Function  of  the  Spinal  Cord,  The  Ar- 
rangement of  Nerve  Cells  in  the  Spinal  Cord,  Columns  and  Tracts  in 
the  White  Matter  of  the  Spinal  Cord,  The  Reflex  Arc  and  Reflex 
Action,  Spinal  Reflexes  in  Man  and  Mammals.  III.  The  Brain 
Stem,  The  Medulla  Oblongata  or  Bulb,  The  Pons  Varolii,  The  Mid- 
brain, The  Optic  Thalami,  The  Cranial  Nerves.  IV.  The  Cere- 
bellum. V.  The  Cerebrum,  Structure  of  the  Cerebral  Cortex,  Gen- 
eral Functions  of  the  Cerebrum,  Localization  of  the  Motor  Function 
of  the  Cerebral  Cortex,  Localization  of  Sensory  Function  in  the  Cere- 
bral Cortex,  Association  Centers  of  the  Cerebral  Cortex,  The  Physiol- 
ogy of  Sleep.     VI.  The  Sympathetic  System,  .....  503 


CONTENTS  Vll 

PAGE 

CHAPTER  XV— The  Senses;  I.  The  Senses  of  Touch,  Pain,  Tem- 
perature, and  the  Muscle  Sense.  II.  Taste  and  Smell,  The  Sense  of 
Taste,  The  Sense  of  Smell.  III.  Hearing  and  Equilibration,  The 
Anatomy  of  the  Ear,  The  Physiology  of  Hearing,  The  Sense  of  Equi- 
librium. IV.  The  Sense  of  Sight,  The  Eye,  The  Optical  Apparatus, 
Accommodation,  Defects  in  the  Optical  Apparatus,  Visual  Sensa- 
tions from  Excitation  of  the  Retina,  Color  Sensations,  Binocular 
Vision,  Visual  Judgments,  Laboratory  Directions  for  Experiments 
on  the  Sense  Organs, 595 

CHAPTER  XVI— The  Reproductive  Organs;  The  Reproductive 
Organs  of  the  Male,  The  Reproductive  Organs  of  the  Female,  Ovu- 
lation and  Menstruation,  Menstrual  Life,       .....  679 

CHAPTER  XVII — Development;  Changes  which  Occur  in  the  Ovum 
Prior  to  Impregnation,  Changes  Following  Impregnation,  Circula- 
tion of  Blood  in  the  Fetus,  Parturition,  Lactation,  .         ,         .         .691 

Index, 701 


FAHRENHEIT 

and 

CENTIGRADE 

SCALES. 


F. 

500° 

401 

392 

383 

374 

356 

347 

338 

329 

320 

311 

302 

284 

275 

266 

248 

239 

230 

212 

203 

194 

176 

167 

140 

122 

113 

105 

104 

100 


95 
86 

77 
68 
50 
41 
32 
23 
14 
+  5 

-  4 

-  13 
-22 
-40 
-76 


C. 
260° 
205 
200 
195 
190 
180 
175 
170 
365 
160 
155 
150 
140 
135 
130 
120 
115 
110 
100 

95 

90 

80 

75 

60 

50 

45 

40.54 

40 

37.8 


36.9 

35 

30 

25 

20 

10 

5 

0 

-  5 

-  10 

-  15 
-20 
-25 
-30 
-40 
-60 


MEASUREMENTS. 

FEENCH  INTO  ENGLISH. 


LENGTH. 

1  metre  ] 

10  decimetres    I    =  39.37  English 
100  centimetres  j  inches. 

1,000  millimetres  J  (or  1  yd.  and  3^  in.) 


1  decimetre      ) 

10  centimetres  V  =  3.937  inches 
100  millimetres  )  (or  nearly  4  inches.) 


1    deg.F.  =  .54°C. 
1.8       "    =    PC. 
3.6       "    =    2°C. 
4.5       "     ^    2.5°C 
5.4       "     =    3°C. 


To  convert  de- 
grees F.  into  de- 
grees C,  subtract 
32,  and  multiply 
by* 


To  convert  de- 
grees C.  into  d^- 
freesF.,  multiply 
y  g,  and  add  32". 


1  centimetre    I   =  .3937  or  about 
10  millimetres   \       (nearly  g  inch.) 
1  millimetre         =  nearly  ^  inch. 

Or, 

One  Metre  =  39.37079  inches. 
(It  is  the  ten-millionth  part  of  a  quarter 

of  the  meridian  of  the  earth.) 

1  Decimetre    =  4  in. 

1  Centimetre  =  T45  in. 

1  Millimetre    =  ^  in. 

Decametre      =  b2.80  feet. 

Hectometre    1=  109.36  yds. 

Kilometre       =  0.62  miles. 
One  incli  =  2.539  Centimetres. 
One  foot  =:  3.047  Decimetres. 
One  yard  =  0.91  of  a  Metre. 
One  mile  =  1.60  Kilometre. 
The  cubic  centimetre  (15.432  grains— 1 
gramme)  is  a  standard  at  4°  O,  the 
grain  at  16°.66  C. 


WEIGHT. 

(One  gramme  is  the  tveight  of  a  cubic 
centimetre  of  water  at  4°  C.  at  Paris). 
1  gramme  ] 

10  decigrammes    |  =  15.432349  grs. 
100  centigrammes  f      (or  nearly  15^). 
1,000  milligrammes  J 


1  decigramme      ) 
10  centigrammes  V  =  rather  more 
100  milligrammes  )     than  1}^  grain. 


1  centigramme     I  =  rather  more 
10  decigrammes    j"     than  5%  grain. 


1  milligramme        =  rather  more 
than  2g^  grain. 
Or 

1  Decigramme  =  2  dr.  34  gr. 

1  Hectogrm.      =  314  oz.  (Avoir.) 

1  Kilogrm.         =  21b.  3  oz.  2 dr.  (Avoir.) 


A  grain  equals  about  1.16  gram., 

a  Troy  oz.  about  31  gram., 

a  lb.  Avoirdupois  about  \j>  Kilogrm., 

and  1  cwt.  about  50  Kilogrms. 


CAPACITY. 

1,000  cubic  decimetres  1  =  1  cubic 
1 ,000,000  cubic  centimetres  \      metre. 


\- 


1  litre. 


1  cubic  decimetre 
or 
1,000  cubic  centimetres 

Or 
One  Litre  =  1  pt.  15  oz.  1  dr.  40. 
(For  simplicity.  Litre  is  used  to  signify 
1  cubic  decimetre,  a  little  less  than  1 
English  quart.) 


Decilitre  (100  c.c.) 
Centilitre  (10  c.c.) 
Millilitre  (1  c.c.) 
Decalitre 
Hectolitre 


=  3^  oz. 
=  2f  dr. 
=  17  m. 
=  21  gal. 
=  22  gals. 


Kilolitre  (cubic  metre)  =  27}^  bushels. 
A  cubic  inch  =  16.38  c.c.  ;  a  cubic  foot 
=  28.315  cubic  d6c,  and  a  gallon  = 
4.54  litres. 


CONVERSION  SCALE. 

To  convert  Grammes  to  Ounces  avoir- 
dupois, multiply  by  20  and  divide  by  567. 

To  convert  Kilogrammes  to  Pounds, 
multiply  by  1,000  and  divide  by  454. 

To  convert  Litres  to  Gallons,  mul- 
tiply by  22  and  divide  by  100. 

To  convert  Litres  to  Pints,  multiply 
by  88  and  divide  by  50. 

To  convert  Millimetres  to  Inches, 
multiply  by  10  and  divide  by  254. 

To  convert  Metres  to  Yards,  multi- 
ply by  70  and  divide  by  64. 


SURFACE   MEASURE. 

1  square  metre  =  about  1550  sq.  inches. 
Or  10,000  sq.  centimetres,  or  10.75  sq.  ft. 
1  sq.  inch  =  about  6  4  sq.  centimetres. 
1  sq.  foot  =       "     930      "         " 


ENERGY  MEASURE. 

1  kilogrammetre=about7.24  ft.  pounds. 
1  foot  pound        =     "      .1381  kgm. 
1  foot  ton  =    "      310  kgm. 


HEAT  EQUIVALENT. 

1  kilocalorie  =  424  kilogrammetres. 


ENGLISH    MEASURES. 

Apothecaries  Weight. 

7000  grains  =  1  lb. 


Or 
437.5  grains  =  1  oz. 


Avoirdupois  Weight. 

16  drams      =  1  oz. 
16  oz.  =  1  lb. 

28  lbs.  c-  1  quarter. 

4  quarters  =  1  cwt. 
20  cwt.  =  1  ton. 


Measure  of  1  decimetre,  or  10  centimetres,  or  100  millimetres. 


J 


1234567S9]fl 
The  micron  (symbol,  m)  is  the  unit  of  microscopic  measurement  =  IB\„j  mm.  =  ^fan  inch. 


HANDBOOK   OF   PHYSIOLOGY 


CHAPTER    I 

THE    PHENOMENA    OF    LIFE 


\ 


Physiology  is  the  science  which  treats  of  the  various  processes  or  changes 
which  take  place  in  the  organs  and  tissues  of  the  body  during  life.  These 
processes,  however,  must  not  be  considered  as  by  any  means  peculiar  to  the 
human  organism,  since,  putting  aside  the  properties  which  serve  to  distinguish 
man  from  other  animals,  the  changes  which  go  on  in  the  tissues  of  man  go  on 
in  much  the  same  way  in  the  tissues  of  all  other  animals  as  long  as  they  live. 
Furthermore  it  is  found  that  similar  changes  proceed  in  all  living  vegetable 
tissues;  they  indeed  constitute  what  are  called  vital  phenomena,  and  are  those 
properties  which  mark  out  living  from  non-living  material. 

The  lowest  types  of  life,  whether  animal  or  vegetable,  are  found  to  consist 
of  minute  masses  of  a  jelly-like  substance,  which  is  generally  known  under  the 
name  of  protoplasm.  Each  such  living  mass  is  called  a  cell,  so  that  these 
minute  elementary  organisms  are  designated  unicellular. 

Not  only  is  it  true  that  the  lowest  types  of  life  are  made  up  of  cells,  but  it 
has  also  been  shown  that  the  tissues  of  which  the  most  complex  organisms  are 
composed  consist  of  cells. 

The  phenomena  of'lije  are  exhibited  in  cells,  whether  existing  alone  or  de- 
veloped into  .'he  orgies  and  tissues  of  animals  and  plants.  It  must  be  at  once 
evident  that  a  correct  knowledge  of  the  nature  and  activities  of  the  cell  forms 
the  very  foundation- of  physiology;  cells  being,  in  fact,  physiological  no  less 
than  morphological  units. 

The  prime  importance  of  the  cell. as  an  element  of  structure  was  first 
established  by  the  researches^ of  the  botanist  Schleiden,  and  his  conclusions, 
drawn  from  the  study  of  vegetable  histology,  were  at  once  extended  by  Theo- 
dor  Schwann  to  the  animal  kingdom.  The  earlier  observers  defined  a  cell 
as  a  more  or  less  spherical  body  limited  by  a  membrane,  and  containing  a 
smaller  body  termed  a  nucleus,  which  in  its  turn  incloses  one  or  more  still 
smaller  bodies  or  nucleoli.  Such  a  definition  applied  admirably  to  most  veg- 
etable cells,  but  the  more  extended  investigation  of  animal  tissues  soon  showed 
that  in  many  cases  no  limiting  membrane  or  cell-wall  could  be  demonstrated. 

The  presence  or  absence  of  a  cell-wall,  therefore,  was  then  regarded  as 
quite  a  secondary  matter,  while  at  the  same  time  the  cell-substance  came 
1  1 


g 


THE    PHENOMENA    OF    LIFE 


•  Space  contain- 
ing liquid. 


....  Protoplasm. 


Nucleus. 


gradually  to  be  recognized  as  of  primary  importance.  Many  of  the  lower 
forms  of  animal  life,  the  Rhizopoda,  were  found  to  consist  almost  entirely 
of  matter  very  similar  in  appearance  and  chemical  composition  to  the  cell- 
substance  of  higher  forms;  and  this  from  its  chemical  resemblance  to  flesh  was 
termed  Sarcode  by  Dujardin.     When  recognized  in  vegetable  cells  it  was  called 

Protoplasm  by  Mulder,  while  Remak  applied 
the  same  name  to  the  substance  of  animal  cells. 
As  the  presumed  formative  matter  in  animal 
tissues  it  was  termed  Blastema,  and  in  the  be- 
lief that,  wherever  found,  it  alone  of  all  sub- 
stances has  to  do  with  generation  and  nutrition, 
Beale  has  named  it  Germinal  matter  or  Bio- 
plasm. Of  these  terms  the  one  most  in  use  at 
the  present  day,  as  we  have  already  said,  is 
protoplasm,  and  inasmuch  as  all  life,  both  in 
the  animal  and  vegetable  kingdoms,  is  associated 
with  protoplasm,  we  are  justified  in  describing 
it,  with  Huxley,  as  the  "  physical  basis  of  life," 
or  simply  "living  matter." 

Properties  of  Protoplasm.  Protoplasm 
is  a  semi-fluid  substance,  which  absorbs  but 
It  is  transparent  and  generally  colorless,  with 
refractive  index  higher  than  that  of  water  but  lower  than  that  of  oil.  It  is 
neutral  or  weakly  alkaline  in  reaction,  but  may  under  special  circumstances 
be  acid,  as,  for  example,  after  activity.  It  undergoes  heat-coagulation  at 
a  temperature  of  about  54. 50  C.  (1300  F.),  and  hence  no  organism  can  live 
when  its  own  temperature  is 
raised  above  that  point.  It  is 
also  coagulated  and  therefore 
killed  by  alcohol,  by  solutions 
of  many  of  the  metallic  salts,  by 
strong  acids  and  alkalies,  and  by 
many  other  chemical  substances. 
Under  the  microscope  it  is 
seen  almost  universally  to  be 
granular,  the  granules  consisting 
of  different  substances,  albu- 
minous, fatty,  or  carbohydrate 
matter.  The  granules  are  not  equally  distributed  throughout  the  whole 
cell-mass,  as  they  are  sometimes  absent  from  the  outer  part  or  layer, 
and  very  numerous  in  the  interior.  In  addition  to  granules,  protoplasm 
generally  exhibits  spaces  or  vacuoles,  usually  globular  in  shape,  except- 
ing during  movement,  when  they  may  be  irregular,  and  filled  with  a  watery 


Cell  wall. 


Fig.  1. — Vegetable  Cells. 


does  not   mix  with  water. 


Nucleus   or   ger- 

—  minal  vesicle. 

—  Nucleolus  or  ger- 

minal spot. 
...  Space  left  by  re- 
traction of  yolk. 

...  Vitellus  or  yolk. 


Vitelline  mem- 
brane. 


Fig.  2. — Semidiagrammatic  Representation  of  a  Human 
Ovum,  showing  the  parts  of  an  animal  cell.     (Cadia.) 


CHARACTERISTICS    OF     PROTOPLASM  3 

fluid.     These  vacuoles  are  more  numerous  and  pronounced  in  vegetable  than 
in  animal  cells.     Gas  bubbles  also  sometimes  exist  in  cells. 

It  is  impossible  to  make  any  definite  statement  as  to  the  exact  chemical 
composition  of  living  protoplasm,  since  the  methods  of  chemical  analysis 
necessarily  imply  the  death  of  the  cell;  it  is,  however,  stated  that  protoplasm 
contains  75  to  85  per  cent  of  water,  and  of  the  15  to  25  per  cent  of  solids  the 
most  important  part  belongs  to  the  class  of  substances  called  proteids  or  al- 
bumins. Proteids  contain  the  chemical  elements  carbon,  hydrogen,  nitrogen, 
oxygen,  sulphur,  and  phosphorus,  the  last  two  in  very  small  quantities  only. 
A  proteid-like  substance,  nuclein,  found  in  the  nuclei  of  cells,  contains  phos- 
phorus in  greater  abundance.  In  the  cell  nucleus  a  compound  of  nuclein 
with  proteid,  called  nucleoproteid,  forms  the  most  abundant  proteid  sub- 
stance.   Other  bodies  are  frequently  found  associated  with  the  proteids,  such 


Fio.  3. — Phases  of  Ameboid  Movement. 

as  glycogen,  starch,  cellulose,  which  contain  the  elements  carbon,  hydrogen,  and 
oxygen,  the  last  two  in  the  proportion  to  form  water,  and  hence  are  termed 
carbohydrates;  jatty  bodies,  containing  carbon,  hydrogen,  and  oxygen,  but  not 
in  proportion  to  form  water;  lecithin,  a  complicated  fatty  body  containing 
phosphorus;  cholesterin,  a  monatomic  alcohol;  chlorophyll,  the  coloring  matter 
of  plants;  inorganic  salts,  particularly  the  chlorides  and  phosphates  of  calcium, 
sodium,  and  potassium ;  ferments,  and  other  substances. 

The  Physiological  Characteristics  of  Protoplasm.  The  properties 
of  protoplasm  may  be  well  studied  in  the  microscopic  animal  called  the 
ameba,  a  unicellular  organism  found  chiefly  in  fresh  water.  These  properties 
may  be  conveniently  studied  under  the  following  heads: — 

The  Power  oj  Spontaneous  Movement.  When  an  ameba  is  observed 
with  a  high  power  of  the  microscope,  it  is  found  to  consist  of  an  irregular  mass 
of  protoplasm  containing  one  or  more  nuclei,  the  protoplasm  itself  being 
more  or  less  granular  and  vacuolated.  If  watched  for  a  minute  or  two,  an 
irregular  projection  is  seen  to  be  gradually  thrust  out  from  the  main  body; 
other  masses  are  then  protruded  until  gradually  the  whole  protoplasmic  sub- 
stance is,  as  it  were,  drawn  over  to  a  new  position,  and  when  this  is  repeated 
several  times  we  have  locomotion  in  a  definite  direction,  together  with  a  con- 
tinual change  of  form.  These  movements,  figure  3,  when  observed  in  other 
cells,  such  as  the  colorless  blood-corpuscles  of  higher  animals,  in  the  branched 
corneal  cells  of  the  frog  and  elsewhere,  are  termed  ameboid. 


4  THE    PHENOMENA    OF     LIFE 

The  remarkable  movement  of  pigment  granules  observed  in  the  branched 
pigment  cells  of  the  frog's  skin  by  Lister  are  also  probably  due  to  ameboid 
movement.  These  granules  are  seen  at  one  time  distributed  uniformly  through 
the  body  and  branched  processes  of  the  cell,  while  at  another  time  they  collect 
in  the  central  mass  leaving  the  branches  quite  colorless. 

This  movement  within  the  pigment  cells  might  also  be  considered  an  ex- 
ample of  the  so-called  streaming  movement  not  infrequently  seen  in  certain 
of  the  protozoa,  in  which  the  mass  of  protoplasm  extends  long  and  fine  pro- 
cesses, themselves  very  little  movable,  but  upon  the  surface  of  which  freely 
moving  or  streaming  granules  are  seen.  A  gliding  movement  has  also  been 
noticed  in  certain  animal  cells;  the  motile  part  of  the  cell  being  composed  of 
protoplasm  bounding  a  central  and  more  compact  mass.  By  means  of  the 
free  movement  of  this  layer,  the  cell  may  be  observed  to  move  along. 

In  vegetable  cells  the  protoplasmic  movement  can  be  well  seen  in  the  hairs 
of  the  stinging-nettle  and  Tradescantia  and  in  the  cells  of  Vallisneria  and 
Chara;  it  is  marked  by  the  movement  of  the  granules  nearly  always  embedded 
in  it.  For  example,  if  part  of  a  hair  of  Tradescantia,  figure  5,  be  viewed 
under  a  high  magnifying  power,  streams  of  protoplasm  containing  crowds  of 


Fig.  4. — Changes  of  Form  of  a  White  Corpuscle,  Sketched  at  Brief  Intervals.     The  figures 
show  also  the  ingestion  of  two  small  granules.      (Schafer.) 


granules  hurrying  along,  like  the  foot-passengers  in  a  busy  street,  are  seen  flow- 
ing steadily  in  definite  directions,  some  coursing  round  the  film  which  lines 
the  interior  of  the  cell-wall,  and  others  flowing  toward  or  away  from  the  irregu- 
lar mass  in  the  center  of  the  cell-cavity.  Many  of  these  streams  of  protoplasm 
run  together  into  larger  ones  and  are  lost  in  the  central  mass,  and  thus  ceaseless 
variations  of  form  are  produced.  The  movement  of  the  protoplasmic  granule? 
to  or  from  the  periphery  is  sometimes  called  vegetable  circulation,  whereas  the 
movement  of  the  protoplasm  round  the  interior  of  the  cell  is  called  rotation. 

The  first  account  of  the  movement  of  protoplasm  was  given  by  Rosel  in 
1755,  as  occurring  in  a  small  Proteus,  probably  a  large  fresh-water  ameba. 
His  description  was  followed  twenty  years  later  by  Corti's  demonstration  of 
the  rotation  of  the  cell  sap  in  characeae,  and  in  the  earlier  part  of  the  century 


CHARACTERISTICS  OF  PROTOPLASM  5 

by  Meyer  in  Vallisneria,  1827;  Robert  Brown,  1831,  in  "Staminal  Hairs  of 
Tradescantia."  Then  came  Dujardin's  description  of  the  granular  streaming 
in  the  pseudopodia  of  Rhizopods  and  movements  in  other  cells  of  animal 
protoplasm  (Planarian  eggs,  von  Siebold,  1841;  colorless  blood-corpuscles, 
Wharton  Jones,  1846). 

The  Power  of  Response  to  Stimuli,  or  Irritability.  Although  the  movements 
of  the  ameba  have  been  described  above  as  spontaneous,  yet  they  may  be  in- 
creased under  the  action  of  external  agencies  which  excite  them  and  are  there- 
fore called  stimuli,  and  if  the  movement  has  ceased  for  the  time,  as  is  the  case  if 
the  temperature  is  lowered  beyond  a  certain  point,  movement  may  be  set  up  by 
raising  the  temperature.     Contact  with  foreign  bodies,  gentle  pressure,  cer- 


Fig.  5. — Cell  of  Tradescantia  Drawn  at  Successive  Intervals  of  two  Minutes. — The  cell-contents 
consist  of  a  central  mass  connected  by  many  irregular  processes  to  a  peripheral  film,  the  whole 
forming  a  vacuolated  mass  of  protoplasm,  which  is  continually  changing  its  shape.      (Schofield.) 

tain  salts,  and  electricity  produce  or  increase  the  movement  in  the  ameba. 
The  protoplasm  is,  therefore,  sensitive  or  irritable  to  stimuli,  and  shows  its  irri- 
tability by  movement  or  contraction  of  its  mass. 

The  effects  of  some  of  these  stimuli  may  be  thus  further  detailed: — 

a.  Changes  of  Temperature.  Moderate  heat  acts  as  a  stimulant;  the  move- 
ment stops  below  o°  C.  (320  F.  ),  and  above  400  C.  (1040  F.);  between  these 
two  points  the  movements  increase  in  activity;  the  optimum  temperature  is 
about  370  to  380  C.  Exposure  to  a  temperature  even  below  o°  C.  stops  the 
movement  of  protoplasm,  but  does  not  prevent  its  reappearance  if  the  tem- 
perature is  raised;  on  the  other  hand,  prolonged  exposure  to  a  temperature 
of  over  400  C.  kills  the  protoplasm  and  causes  it  to  enter  into  a  condition  of 
coagulation  or  heat  rigor. 

b.  Mechanical  Stimuli.  When  gently  squeezed  between  a  cover  and 
object-glass  under  proper  conditions,  a  colorless  blood-corpuscle  contracts 
and  ceases  its  ameboid  movement. 

c.  Nerve  Influence.  By  stimulation  of  the  nerves  of  the  frog's  cornea, 
contraction  of  certain  of  its  branched  cells  has  been  produced. 

d.  Chemical  Stimuli.  Water  generally  stops  ameboid  movement,  and  by 
imbibition  causes  great  swelling  and  finally  bursting  of  the  cells.  In  some 
cases,  however  (myxomycetes),  protoplasm  can  be  almost  entirely  dried  up, 
but  remains  capable   of  renewing   its  movements  when  again  moistened. 


G 


THE     PHENOMENA     OF     LIFE 


Dilute  salt-solution  and  many  dilute  acids  and  alkalies  stimulate  the  move- 
ments temporarily.  Strong  acids  or  alkalies  permanently  stop  the  movements; 
ether,  chloroform,  veratrium,  and  quinine  also  stop  it  for  a  time. 

Movement  is  suspended  in  an  atmosphere  of  hydrogen  or  carbonic  acid 
and  resumed  on  the  admission  of  air  or  oxygen,  but  complete  withdrawal  of 
oxygen  will  after  a  time  kill  the  protoplasm. 

e.  Electrical.  Weak  currents  stimulate  movement,  while  strong  currents 
cause  the  cells  to  assume  a  spherical  form  and  to  become  motionless. 

The  Power  oj  Digestion,  Respiration,  and  Nutrition.  This  consists  in  the 
power  which  is  possessed  by  the  ameba  and  similar  animal  cells  of  taking  in 
food,  modifying  it,  building  up  tissue  by  assimilating  it,  and  rejecting  what  is 
not  assimilated.  These  various  processes  are  effected  in  some  one-celled  ani- 
mals by  the  protoplasm  simply  flowing  around  and  enclosing  within  itself 
minute  organisms  such  as  diatoms  and  the  like.  From  these  it  extracts  what 
it  requires,  and  then  rejects  or  excretes  the  remainder,  which  has  never  formed 
part  of  the  body.  This  latter  proceeding  is  done  by  the  cell  withdrawing 
itself  from  the  material  to  be  excreted.     The  assimilation  constantly  taking 

place  in  the  body  of  the  ameba  is  for  the  pur- 
pose of  replacing  waste  of  its  tissue  consequent 
upon  manifestation  of  energy.  The  respiratory 
process  of  absorbing  oxygen  goes  on  at  the  same 
time. 

The  processes  which  take  place  in  cells, 
both  animal  and  vegetable,  are  summed  up 
under  the  term  metabolism  (from  pera/So^, 
change).  The  changes  which  go  on  are  of  two 
kinds,  viz.,  assimilation,  or  building  up,  and 
disassimilation,  or  breaking  down ;  they  may 
be  also  called,  using  the  nomenclature  of  Gas- 
kell,  anabolism  or  constructive  metabolism,  and 
catabolism  or  destructive  metabolism.  In  the 
direction  of  anabolism  two  processes  occur, 
viz.,  the  building  up  of  materials  which  it 
takes  in,  and  secondly,  the  building  up  of  its 
own  substance  by  those  or  other  materials. 
As  we  shall  see  in  a  subsequent  paragraph, 
the  process  of  anabolism  differs  to  some  ex- 
tent in  vegetable  and  animal  cells.  The  catab- 
olism of  the  cell  consists  in  chemical  changes  which  occur  in  the  cell- 
substance  itself,  or  in  substances  in  contact  with  it. 

The  destructive  metabolism  of  a  cell  is  increased  by  its  activity,  but  goes 
on  also  during  quiescence.  It  is  probably  of  the  nature  of  oxidation,  and  re- 
sults in  the  evolution  of  carbon  dioxide  and  water  on  the  one  hand,  and  in  the 


Fig.  6. — Cells  from  the  Staminal 
Hairs  of  Tradescantia.  A,  Fresh 
in  water;  B,  the  same  cell  after 
slight  electrical  stimulation;  a,  b, 
region  stimulation;  c,  d,  clumps 
and  knobs  of  contracted  proto- 
plasm.    (Kiihne.) 


CHARACTERISTICS    OF     PROTOPLASM 


formation  of  various  more  complex  chemical  substances  on  the  other,  some  of 
which  may  be  stored  up  in  the  cell  for  future  use,  and  are  called  secretions, 
and  others,  like  carbon  dioxide,  for  example,  and  bodies  containing  nitrogen, 
are  eliminated  as  excretions. 

The  Power  of  Growth.  In  protoplasm  it  is  seen  that  the  two  processes  of 
waste  and  repair  go  on  side  by  side,  and  so  long  as  they  are  equal  the  size 
of  the  animal  remains  stationary.  If,  however,  the  building  up  exceed  the 
waste,  then  the  animal  grows;   if  the  waste  exceed  the  repair,  the  animal 


Fig.  7. — Diagram  of  an  Ovum  (a)  Undergoing  Segmentation.  In  (b)  it  has  divided  into  two, 
in  (c)  into  four;  and  in  (d)  the  process  has  ended  in  the  production  of  the  so-called  "mulberry  mass." 
(Frey.) 

decays;  and  if  decay  go  on  beyond  a  certain  point,  life  becomes  impossible, 
and  the  animal  dies. 

The  power  of  increasing  in  size,  although  essential  to  our  idea  of  life,  is  not, 
it  must  be  recollected,  confined  to  living  beings.  A  crystal  of  common  salt, 
for  example,  if  placed  under  appropriate  conditions  for  obtaining  fresh  mate- 
rial, will  increase  in  size  in  a  fashion  as  definitely  characteristic  and  as  easily 
to  be  foretold  as  that  of  a  Jiving  creature;  but  the  growth  of  a  crystal  takes 
place  merely  by  additions  to  its  outside;  the  new  matter  is  laid  on  particle  by 
particle,  and  layer  by  layer,  and,  when  once  laid  on,  it  remains  unchanged.  In 
a  living  structure,  where  growth  occurs,  it  is  by  addition  of  new  matter,  not 
to  the  surface  only,  but  throughout  every  part  of  the  mass,  and  this  matter  be- 
comes an  intimate  part  of  the  living  substance. 

The  Power  oj  Reproduction.  The  ameba,  to  return  to  our  former  illus- 
tration, when  the  growth  of  its  protoplasm  has  reached  a  certain  point,  mani- 
fests the  power  of  reproduction,  by  splitting  up  into  (or  in  some  other  way  pro- 
ducing) two  or  more  parts,  each  of  which  is  capable  of  independent  existence. 
The  new  amebae  manifest  the  same  properties  as  the  parent,  perform  the  same 
functions,  grow  and  reproduce  in  their  turn.  This  cycle  of  life  is  being  con- 
tinually passed  through. 

In  more  complicated  structures  than  the  ameba,  the  life  of  individual 
protoplasmic  cells  is  probably  very  short  in  comparison  with  that  of  the  organ- 
ism they  compose;  and  their  constant  decay  and  death  necessitate  constant  re- 
production. The  mode  in  which  this  takes  place  has  long  been  the  subject  of 
controversy. 

It  is  now  very  generally  believed  that  every  cell  is  descended  from  some 
pre-existing  mother  cell.  This  derivation  of  cells  from  cells  takes  place  by 
gemmation,  which  essentially  consists  in  the  budding  off  and  separation  of 
a  portion  of  the  parent  cell;  or  by  fission  or  division. 


8 


THE    PHENOMENA    OF    LIFE 


The  exact  manner  of  the  division  of  cells  is  a  matter  of  some  difficulty,  and 
will  not  be  described  until  the  subject  of  the  structure  of  protoplasmic  cells  has 
been  considered. 

STRUCTURE   OF   PROTOPLASM. 

Elemental  Structure.  Protoplasm  was  formerly  thought  to  be 
homogeneous.  It  is  now  generally  found  to  consist  of  the  elemental  divisions 
called  cells.  Each  cell,  from  a  morphological  point  of  vr  :  consists  of  dif- 
ferentiated parts,  the  most  constant  of  which  are  the  cell  nucleus  and  the  cell 
cytoplasm.  The  cytoplasm  is  differentiated  further  into  two  substances, 
spongioplasm  and  hyaloplasm.  ""The  spongioplasm  or  reticulum  forms  a  fine 
network,  increases  in  relative  amount  as  the  cell  grows  older,  and  has  an 
affinity  for  staining  reagents.  The  hyaloplasm  is  less  refractile,  elastic,  or 
extensile,  and  has  little  or  no  affinity  for  stains;  it  predominates  in  young  cells 


Cell  membrane 


Cell  reticulum.. 


Membrane  of  nucleus. 


..Achromatic  substance  of 

nucleus. 
-  Chromatic    substance    of 

nucleus. 


FlG.  8. — Cell  with  its  Reticulum   Disposed  Radially;  from  the  intestinal  epithelium  of   a 

worm.     (Carnoy.) 

is  thought  to  be  fluid,  and  fills  the  interspaces  of  the  reticulum.  The  nodal 
points  of  the  reticulum,  with  the  granular  microsomes,  found  in  the  proto- 
plasm, cause  the  granular  appearance. 

The  arrangement  of  the  reticulum  varies  considerably  in  different  cells,  and 
even  in  different  parts  of  the  same  cell.  Sometimes,  for  example,  figure  8, 
the  meshwork  has  an  elongated  radial  arrangement  from  the  nucleus;  at 
others,  the  meshwork  is  more  evenly  disposed,  as  in  figure  9.  At  the  junctions 
of  the  fibrils  there  are  usually  slight  enlargements  or  nodes. 

In  some  cells,  particularly  in  plants,  but  also  in  some  animal  cells,  there  is 
a  tendency  toward  a  formation  of  a  firmer  external  envelope,  constituting  in 
vegetable  cells  a  membrane  distinct  from  the  more  central  and  more  fluid  part 
of  the  protoplasm.  In  such  cases  the  reticulum  at  the  periphery  of  the  cell  is 
made  up  of  very  fine  meshes.  The  membrane  when  formed  is  usually  pierced 
with  pores  by  which  fluid  may  pass  in,  or  through  which  protrusion  of  the 
protoplasmic  filaments  forming  the  cell's  connection  with  other  cells  surround- 
ing it  may  take  place. 


STRUCTURE     OF     PROTOPLASM  9 

It  is  an  exceedingly  interesting  question  whether  in  cells  the  one  part  of  the 
protoplasm  can  exist  without  the  other.  Schafer  summarizes  the  matter  thus: 
"  There  are  cells,  and  unicellular  organisms  both  animal  and  vegetable,  in 
which  no  reticular  structure  can  be  made  out,  and  these  may  be  formed  of 
hyaloplasm  alone.  In  that  case,  this  must  be  looked  upon  as  the  essential 
part  of  protoplasm.  So  far  as  ameboid  phenomena  are  concerned  it  is  cer- 
tainly so;  but  whether  the  chemical  changes  which  occur  in  many  cells  are 
effected  by  this  or  by  spongioplasm  is  another  matter." 

The  Cell  Nucleus.  All  cells  at  some  period  of  their  existence  pos- 
sess nuclei.  The  origin  of  a  nucleus  in  a  cell  is  the  first  trace  of  the  differentia- 
tion of  protoplasm.     The  existence  of  nuclei  was  first   pointed   out   in   the 


Fig.  g. — A:  The  Colorless  Blood -Corpuscle,  Showing  the  Intracellular  Network,  and  two 
nuclei  with  intranuclear  network.  B:  Colored  blood-corpuscle  of  newt  showing  the  intracellular 
network  of  fibrils.  Also  oval  nucleus  composed  of  limiting  membrane  and  fine  intranuclear  net- 
work of  fibrils.      X  800.     (Klein  and  Noble  Smith.) 

year  1833  by  Robert  Brown,  who  observed  them  in  vegetable  cells.  They  are 
either  small  transparent  vesicular  bodies  containing  one  or  more  smaller  parti- 
cles called  nucleoli,  always  when  in  the  resting  condition  bounded  by  a  well- 
defined  envelope.  In  their  relation  to  the  life  of  the  cell  they  are  certainly 
hardly  second  in  importance  to  the  cytoplasm  itself,  and  thus  Beale  is  fully 
justified  in  comprising  both  under  the  term  "germinal  matter."  They  con- 
trol the  nutrition  of  the  cell,  and  probably  initiate  the  process  of  subdivision. 
If  a  cell  be  mechanically  divided,  that  portion  not  containing  the  nucleus  dies. 

Histologists  have  long  recognized  certain  important  characters  of  nuclei. 
One  is  their  power  of  resisting  the  action  of  various  acids  and  alkalies,  particu- 
larly acetic  acid,  by  which  their  outlines  are  more  clearly  defined,  and  they  are 
rendered  more  easily  visible.  Another  is  their  quality  of  staining  in  solu- 
tions of  carmine,  hematoxylin,  etc.  This  indicates  some  chemical  difference 
between  the  cytoplasm  of  the  cells  and  their  nuclei,  as  the  former  is  destroyed 
by  these  reagents. 

Nuclei  are  most  commonly  oval  or  round,  and  do  not  necessarily  conform  to 
the  diverse  shapes  of  the  cells;  they  are  altogether  less  variable  elements  than 
cells,  even  in  regard  to  size,  of  which  fact  one  may  see  a  good  example  in  the 
uniformity  of  the  nuclei  in  cells  so  multiform  as  those  of  epithelium.  But 
sometimes  nuclei  occupy  almost  the  whole  of  the  cell,  as  in  the  lymph  corpuscles 


10 


THE     PHENOMENA     OF    LIFE 


of  lymphatic  glands,  and  in  some  small  nerve  cells.  Their  position  in  the  cell 
is  very  variable.  In  many  cells,  especially  where  active  growth  is  progressing, 
two  or  more  nuclei  are  present. 

Cell  Division  and  Growth.  The  division  of  a  cell  is  preceded  by 
division  of  its  nucleus,  which  may  be  either  direct  or  indirect.  Direct  or  simple 
division,  amitosis  or  akinesis,  see  figure  10,  occurs  without  any  change  in  the 
arrangement  of  the  intranuclear  network.  A  constriction  develops  at  the  cen- 
ter of  the  nucleus,  possibly  preceded  by  division  of  the  nucleoli,  and  gradually 
divides  \t  into  two  equal  daughter  nuclei.  A  similar  constriction  of  the  pro- 
toplasm of  the  cell  occurs  between  the  daughter  nuclei  and  divides  it  into  two 
parts. 

Indirect  division,  mitosis,  or  karyokinesis  is  the  usual  method,  and  consists 
of  a  series  of  changes  in  the  arrangement  of  the  intranuclear  network,  resulting 


Fig.  io. — Akinesis,  Amitosis,  or  Direct  Cell  Division.  A,  Constriction  of  nucleus;  B,  divjsion 
of  nucleus  and  constriction  of  cell  body;  C,  daughter  nuclei  still  connected  by  a  thread,  division 
being  delayed;   D,  division  of  cell  body  nearly  complete.     (After  Arnold.) 


in  the  exact  division  of  the  chromatic  fibers  into  two  parts,  which  form  the 
chromoplasm  of  the  daughter  nuclei.  The  changes  follow  a  closely  similar 
course  in  both  plant  and  animal  cells. 

Differences  between  Animals  and  Plants.  Having  considered  at 
some  length  the  vital  properties  of  protoplasm,  as  shown  in  cells  of  animal 
as  well  as  of  vegetable  organisms,  we  are  now  in  a  position  to  discuss  the  ques- 
tion of  the  differences  between  plants  and  animals.  It  might  at  the  outset 
of  our  inquiry  have  seemed  an  unnecessary  thing  to  recount  the  distinctions 
which  exist  between  an  animal  and  a  vegetable  as  they  are  in  many  cases  so 
obvious,  but,  however  great  the  differences  may  be  between  the  higher  animals 
and  plants,  in  the  lowest  of  them  the  distinctions  are  much  less  plain. 

In  the  first  place,  it  is  important  to  lay  stress  upon  the  differences  between 
vegetable  and  animal  cells,  first  as  regards  their  structures  and  next  as  re- 
gards their  functions. 


DIFFERENCES     BETWEEN     ANIMALS     AND     PLANTS 


11 


It  has  been  already  mentioned  that  in  animal  cells  an  envelope  or  cell-wall 
is  by  no  means  always  present.  In  adult  vegetable  cells,  on  the  other  hand, 
a  well-defined  wall  is  highly  characteristic;  this  is  composed  of  cellulose, 
is  non-nitrogenous,  and  thus  differs  chemically  as  well  as  structurally  from  the 
contained  protoplasmic  mass.     Moreover,  in  vegetable  cells,  figure  12,  B,  the 


Fig.  11. — Karyokinesis,  Mitosis,  or  Indirect  Cell  Division  (diagrammatic).  A,  Cell  with  rest- 
ing nucleus;  B,  wreath,  daughter  centrosomes  and  early  stage  of  achromatic  spindle;  C,  chromo- 
somes; D,  monaster  stage,  achromatic  spindle  in  long  axis  of  nucleus,  chromosomes  dividing; 
£,  chromosomes  moving  toward  centrosomes;  F,  diaster  stage,  chromosomes  at  poles  of  nucleus, 
commencing  constriction  of  cell  body;  G,  daughter  nuclei  beginning  return  to  resting  state;  H, 
daughter  nuclei  showing  monaster  and  wreath;  /,  complete  division  of  cell  body  into  daughter 
cells  whose  nuclei  have  returned  to  the  resting  state.     (After  Bohm  and  von  Davidoff.) 

protoplasmic  contents  of  the  cell  fall  into  two  subdivisions:  1,  a  continuous 
film  which  lines  the  interior  of  the  cellulose  wall;  and,  2,  a  reticulate  mass  con- 
taining the  nucleus  and  occupying  the  cell-cavity.  The  interstices  are  filled 
with  fluid.     In  young  vegetable  cells  such  a  distinction  does  not  exist;    a 


Pig.  12. — A.  Young  Vegetable  Cells, Showing  Cell-Cavity  Entirely  Filled  with  Granular  Pro- 
toplasm Enclosing  a  Large  Oval  Nucleus,  with  one  or  more  Nucleoli.  B.  Older  cells  from  same 
plant,  showing  distinct  cellulose- wall  and  vacuolation  of  protoplasm. 

finely  granular  protoplasm  occupies  the  whole  cell-cavity,  figure  12,  A.  As 
regards  the  respective  functions  of  animal  and  vegetable  cells,  one  of  the 
most  important  differences  consists  in  the  power  which  vegetable  cells  possess 
of  being  able  to  build  up  new  complicated  nitrogenous  and  non-nitrogenous 


12  THE    PHENOMENA    OF     LIFE 

bodies  out  of  very  simple  chemical  substances  obtained  from  the  air  and  from 
the  soil.  They  obtain  from  the  air  oxygen,  carbon  dioxide,  and  water,  as 
well  as  traces  of  ammonia  gas;  and  from  the  soil  they  obtain  water,  ammonium 
salts,  nitrates,  sulphates,  and  phosphates  in  combination  with  such  bases  as 
potassium,  calcium,  magnesium,  sodium,  iron,  and  others.  The  majority 
of  plants  are  able  to  work  up  these  elementary  compounds  into  other  and  more 
complicated  bodies.  This  they  are  able  to  do  in  consequence  of  their  contain- 
ing a  certain  coloring  matter  called  chlorophyll,  the  presence  of  which  is  the 
cause  of  the  green  hue  of  plants.  In  all  plants  which  contain  chlorophyll  two 
processes  are  constantly  going  on  when  they  are  exposed  to  light:  one,  which 
is  called  true  respiration  and  is  a  process  common  to  animal  and  vegetable 
cells  alike,  consists  in  the  taking  of  the  oxygen  from  the  atmosphere  and  the 
giving  out  of  carbon  dioxide;  the  other,  which  is  peculiar  apparently  to  bodies 
containing  chlorophyll,  consists  in  the  taking  in  of  carbon  dioxide  and  the 
giving  out  of  oxygen.  It  seems  that  the  chlorophyll  is  capable  of  decomposing 
the  carbon  dioxide  gas  and  of  fixing  the  carbon  in  the  structures  in  the  form  of 
new  compounds,  one  of  the  most  rapidly  formed  of  which  is  starch. 

Vegetable  protoplasm  by  the  aid  of  its  chlorophyll  is  able  to  build  up  a  large 
number  of  bodies  besides  starch,  the  most  interesting  and  important  being 
proteid  or  albumin.  It  appears  to  be  a  fact  that  the  power  which  bodies  pos- 
sess of  being  able  to  synthesize  is  to  a  large  extent  dependent  upon  the  chloro- 
phyll they  contain.  Thus  the  power  is  present  to  a  marked  extent  only  in  the 
plants  in  which  chlorophyll  is  found,  and  is  absent  in  those  which  do  not 
possess  it.  It  is  probably  present  only  in  slight  degree  as  one  of  the  proper- 
ties of  animal  protoplasm. 

It  must  be  recollected,  however,  that  chlorophyll  without  the  aid  of  the 
light  of  the  sun  can  do  nothing  in  the  way  of  building  up  substances,  and  a 
plant  containing  chlorophyll  when  placed  in  the  dark,  while  it  continues  to  live, 
and  that  is  not  as  a  rule  long,  acts  as  though  it  did  not  contain  any  of  that  sub- 
stance. It  is  an  interesting  fact  that  certain  of  the  bacteria  have  the  chlorophyll 
replaced  by  a  similar  pigment  which  is  able  to  decompose  carbon  dioxide  gas. 

Animal  cells  do  not  possess  the  power  of  building  up  or  synthesizing  from 
simple  materials;  their  activity  is  chiefly  exercised  in  the  opposite  direction, 
viz.,  they  have  brought  to  them  as  food  the  complicated  compounds  produced 
by  the  vegetable  kingdom.  With  these  foods  they  are  able  to  perform  their 
complex  functions,  setting  free  energy  in  the  direction  of  heat,  motion,  and 
electricity,  and  at  the  same  time  eliminating  such  bodies  as  carbon  dioxide  and 
water,  and  producing  other  bodies,  many  of  which  contain  nitrogen,  but  are 
derived  from  decomposition. 

With  reference  to  the  substance  chlorophyll  it  is  necessary  to  say  a  few 
words.  It  has  been  noted  that  the  synthetical  operations  of  vegetable  cells  are 
peculiarly  associated  with  the  possession  of  chlorophyll  and  that  these  opera- 
tions are  dependent  upon  the  light  of  the  sun.     It  has  been  further  shown  that 


DIFFERENCES     BETWEEN     ANIMALS    AND     PLANTS  13 

a  solution  of  chlorophyll  has  a  definite  absorption  spectrum  when  examined 
with  the  spectroscope,  and  that  it  is  particularly  those  parts  of  the  solar  spec- 
trum corresponding  to  these  absorption  bands  which  are  chiefly  active  in  the 
decomposition  of  carbon  dioxide.  In  the  synthetical  processes  of  the  plant 
then,  by  aid  of  its  chlorophyll,  the  radiant  energy  of  the  sun's  rays  becomes 
stored  up  or  rendered  potential  in  the  chemical  products  formed.  The  poten- 
tial energy  is  set  free,  or  is  again  made  kinetic,  when  these  products  simply  by 
combustion  produce  heat,  or  when  they  are  taken  into  the  animal  organism 
and  used  as  food  and  to  produce  heat  and  motion. 

The  influence  of  light  is  not  an  absolute  essential  to  animal  life;  indeed,  it 
is  said  not  to  increase  the  metabolism  of  animal  tissue  to  any  great  extent, 
and  the  animal  cell  does  not  receive  its  energy  directly  from  the  sun's  light, 
nor  yet  to  any  extent  from  the  sun's  heat,  but  from  the  potential  energy  of  the 
food  stuffs.  But  it  must  be  always  kept  in  mind  that  anabolism  is  not  peculiar 
to  vegetable,  or  katabolism  to  animal  cells;  both  processes  go  on  in  each. 
Some  of  the  lowest  forms  of  vegetable  life,  e.g.,  the  bacteria,  will  live  only  in  a 
highly  albuminous  medium,  and  in  fact  seem  to  require  for  their  growth 
elements  of  food  stuffs  which  are  essential  to  animal  life.  In  their  metabolism, 
too,  they  very  closely  approximate  animal  cells,  not  only  requiring  an  atmos- 
phere of  oxygen,  but  giving  out  carbon  dioxide  freely,  and  secreting  and  excret- 
ing many  very  complicated  nitrogenous  bodies,  as  well  as  forming  proteid, 
carbohydrates,  and  fat,  requiring  heat  bdt  not  light  for  the  due  performance 
of  their  functions.     Certain  bacteria  grow  only  in  the  absence  of  oxygen. 

There  is,  commonly,  a  difference  in  general  chemical  composition  between 
vegetables  and  animals,  even  in  their  lowest  forms;  for  associated  with  the 
protoplasm  of  the  former  is  a  considerable  amount  of  cellulose,  a  substance 
closely  allied  to  starch  and  containing  carbon,  hydrogen,  and  oxygen  only. 
The  presence  of  cellulose  in  animals  is  much  rarer  than  in  vegetables,  but  there 
are  many  animals  in  which  traces  of  it  may  be  discovered,  and  some  in  which 
it  is  found  in  considerable  quantity.  The  presence  of  starch  in  vegetable  cells 
is  very  characteristic,  though,  as  we  have  seen  above,  it  is  not  distinctive,  and 
a  substance,  glycogen,  similar  in  composition  to  starch,  is  very  common  in  the 
organs  and  tissues  of  animals. 

Inherent  power  of  movement  is  a  quality  which  we  so  commonly  consider 
an  essential  indication  of  animal  nature  that  it  is  difficult  at  first  to  conceive  of 
its  existence  in  any  other.  The  capability  of  simple  motion  is  now  known, 
however,  to  exist  in  so  many  vegetable  forms  that  it  can  no  longer  be  held 
as  an  essential  distinction  between  them  and  animals,  and  ceases  to  be  a  mark 
by  which  the  one  can  be  distinguished  from  the  other.  Thus  the  zoospores  of 
many  of  the  Cryptogams  exhibit  ciliary  or  ameboid  movements  of  a  like 
kind  to  those  seen  in  amebae;  and  even  among  the  higher  orders  of  plants, 
many,  e.g.,  Dioncea  muscipula  (Venus's  fly-trap),  and  Mimosa  sensitiva  (Sensi- 
tive plant)  exhibit  such  motion,  either  at  regular  times  or  on  the  applica- 


14 


THE    PHENOMENA     OF     LIFE 


tion  of  external  irritation,  as  might  lead  one,  were  this  fact  taken  by  itself,  to 
regard  them  as  sentient  beings.  Inherent  power  of  movement,  then,  al- 
though especially  characteristic  of  animal  nature,  is,  when  taken  by  itself,  no 
proof  of  it. 

Cell  Differentiation  and  the  Functions  of  Organized  Cells.  As  we 
proceed  upward  in  the  scale  of  life  from  the  unicellular  organisms,  we  find 
another  phenomenon  exhibited  in  the  life  history  of  the  higher  forms,  namely, 
that  of  development.  The  one-celled  ameba  comes  into  being  derived  from 
a  previous  ameba;  it  manifests  the  properties  and  performs  the  functions  of 
its  life  which  have  been  already  enumerated.  In  the  higher  organisms  it  is 
different.  Each,  indeed,  begins  as  a  single  cell,  but  the  cells  which  result  from 
division  and  subdivision  do  not  form  so  many  independent  organisms,  but 
adhere  in  one  differentiated  community  which  ultimately  forms  the  complex 
but  co-ordinated  whole,  in  man  the  human  body. 

Thus,  from  the  ovum,  or  germ  cell  which  forms  the  starting-point  of  ani- 
mal life,  in  a  comparatively  short  time  there  is  formed  a  complete  membrane 
of  cells,  polyhedral  in  shape  from  mutual  pressure,  called  the  Blastoderm;  and 


Fig.  13. — Transverse  Section  through  Embryo  Chick  (26  hours),  a,  Epiblast;  b,  mesoblast; 
c,  hypoblast;  d,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast;  e,  primitive 
groove;   /,  dorsal  ridge.     (Klein.) 


this  speedily  differentiates  into  two  and  then  into  three  layers,  chiefly  from 
the  rapid  proliferation  of  the  cells  of  the  first  single  layer.  These  layers, 
figure  13,  are  called  the  Epiblast,  the  Mesoblast,  and  the  Hypoblast.  In  the 
further  development  of  the  animal  it  is  found  that  from  each  of  these  layers  is 
produced  a  very  definite  part  of  the  completed  body.  For  example,  from 
the  cells  of  the  epiblast  are  derived,  among  other  structures,  the  skin  and  the 
central  nervous  system;  from  the  mesoblast  the  muscles  and  connective 
tissue  of  the  body,  and  from  the  hypoblast  the  epithelium  of  the  alimentary 
canal,  some  of  the  chief  glands,  and  so  on. 

It  is  obvious  that  the  tissues  and  organs  so  derived  will  exhibit  in  a  varying 
degree  the  primary  properties  of  protoplasm.  The  muscles,  for  example, 
derived  chiefly  from  certain  cells  of  the  mesoblast  are  particularly  contractile 
and  respond  to  stimuli  readily,  while  the  cells  of  the  liver,  although  possibly 
contractile  to  a  certain  extent,  have  to  do  chiefly  with  the  processes  of  nutrition. 


SOURCES     AND     UTILIZATION     OF    PHYSIOLOGICAL    MATERIAL  15 

As  the  cells  of  the  embryo  increase  in  number  in  development  there  is  a 
corresponding  differentiation  of  function  among  the  groups  of  cells.  The 
various  functions  which  the  original  cell  may  be  supposed  to  discharge,  and 
the  various  properties  it  may  be  supposed  to  possess,  become  divided  among 
groups  of  cells  in  which  the  work  of  each  group  is  specialized.  As  a  result 
of  this  division  of  labor  the  functions  and  properties  are  developed  and  made 
more  perfect,  with  a  view  to  the  more  economic  and  effective  accomplishment 
of  the  activities  of  the  body  as  a  whole. 

In  studying  the  functions  of  the  human  body  it  is  necessary  first  of  all  to 
know  of  what  it  is  composed,  of  what  tissues  and  organs  it  is  made  up;  this 
can  of  course  be  ascertained  only  by  the  dissection  of  the  dead  body,  and  thus 
it  comes  that  Anatomy,  the  science  which  treats  of  the  structure  of  organized 
bodies,  is  closely  associated  with  physiology,  which  treats  of  the  function  of 
the  same  structures.  So  close,  indeed,  is  the  association  that  Histology, 
which  is  especially  concerned  with  the  minute  or  microscopic  structure  of  the 
tissues  and  organs  of  the  body,  and  which  is  strictly  speaking  a  department 
of  anatomy,  is  often  included  in  works  on  physiology.  There  is  much  to  be 
said  in  favor  of  such  an  arrangement,  since  it  is  impossible  to  consider  the 
changes  which  take  place  in  any  tissue  during  life,  apart  from  the  knowledge 
of  the  structure  of  the  tissues  themselves.  There  is  indeed  an  almost  insep- 
arable relation  between  the  structure  and  the  function  of  the  differentiated 
animal  body  in  which  the  one  is  made  the  means  to  a  knowledge  of  the  other  as 
an  end,  and  vice  versa,  according  to  the  aims  and  purposes  of  the  student. 

An  equally  important  essential  to  the  right  comprehension  of  the  changes 
which  take  place  in  the  living  organism  is  a  knowledge  of  the  chemical  com- 
position of  the  body.  Here,  however,  we  can  deal  directly  only  with  the 
composition  of  the  dead  body,  and  it  is  well  at  once  to  admit  that  there  may 
be  many  chemical  differences  between  living  and  non-living  tissues;  but  as  it 
is  impossible  to  ascertain  the  exact  chemical  composition  of  the  living  tissues, 
the  next  best  thing  which  can  be  done  is  to  find  out  as  much  as  possible  about 
the  composition  of  the  same  tissues  after  they  are  dead.  This  is  the  assistance 
which  the  science  of  Chemistry  can  afford  to  the  physiologist. 

Having  mastered  the  structure  and  composition  of  the  body,  we  are  brought 
face  to  face  with  physiology  proper,  and  have  to  investigate  the  vital  changes 
which  go  on  in  the  tissues,  the  various  actions  taking  place  as  long  as  the  or- 
ganism is  at  work.  The  subject  includes  not  only  the  observation  of  the  mani- 
fest processes  which  are  continually  taking  place  in  the  healthy  body,  but 
the  conditions  under  which  these  are  brought  about,  the  laws  which  govern 
them  and  their  effects. 

Sources  and  Utilization  of  Physiological  Material.  It  may  be  well 
to  mention  as  a  preliminary  that  the  physiological  information  which  we  have 
at  our  disposal  has  been  derived  from  many  sources,  the  chief  of  which  are 
as  follows:     From  actual  observation  of  the  various  phenomena  occurring  in 


16  THE    PHENOMENA     OF     LIFE 

the  human  body  from  day  to  day,  and  from  hour  to  hour,  as,  for  example,  the 
estimation  of  the  amount  and  composition  of  the  ingesta  and  egesta,  the  res- 
piration, the  beat  of  the  heart,  and  the  like;  from  observations  upon  other 
animals,  the  bodies  of  which  we  are  taught  by  comparative  anatomy  approxi- 
mate the  human  body  in  structure  and  may  be  supposed  to  be  similar  in  function; 
from  observations  of  the  changes  produced  by  experiment  upon  the  various 
processes  in  such  animals,  or  in  the  organs  and  tissues  of  animals;  from  ob- 
servations of  the  changes  in  the  working  of  the  human  body  produced  by  dis- 
eases; from  observations  upon  the  gradual  changes  which  take  place  in  the 
functions  of  organs  when  watched  in  the  embryo  from  their  earliest  beginnings 
to  their  completed  development. 

The  physiologist,  in  order  to  utilize  the  sources  of  material,  must  be  familiar 
with  the  gross  structure  of  the  animals  or  parts  of  animals  which  he  proposes 
to  use  in  experimental  procedure.  So  simple  a  matter  as  the  determination  of 
arterial  blood  pressure  involves  familiarity  with  extensive  anatomical  structure. 
Experimental  procedure  must  also  draw  on  the  field  of  microscopic  structure 
or  histology,  and  many  of  the  most  instructive  bodies  of  physiological  knowledge 
have  come  directly  from  the  utilization  of  the  facts  of  comparative  anatomy 
and  of  biology.  The  problems  in  animal  nutrition  which  are  under  such  ex- 
tensive investigation  at  the  present  time  require  for  their  solution  not  only 
the  use  of  the  most  complex  methods  of  chemistry,  both  analytical  and  synthet- 
ical, but  also  the  principles  and  methods  of  physics.  Indeed,  since  the  work 
of  Helmholz,  the  interpretation  of  physiological  phenomena  by  means  of  physi- 
cal laws  and  methods  has  contributed  more  than  any  other  means  toward  the 
prominent  scientific  position  of  physiology  at  the  present  time.  In  a  word, 
physiology  must  utilize  the  facts  of  anatomy,  histology,  biology,  physics,  and 
chemistry  to  interpret  the  phenomena  of  life. 


CHAPTER  II 

CELL    DIFFERENTIATION    AND    THE    STRUCTURE    OF   THE 
ELEMENTARY    TISSUES 

A  careful  examination  of  the  human  body  shows  that  the  functional  unit 
for  the  various  and  complicated  life  phenomena  is  the  microscopical  structure, 
the  cell.  The  cell,  alone  or  in  combination,  is  capable  of  all  the  activities 
manifested  by  the  living  body.  As  a  basis  for  brief  review  of  the  elementary 
structures  of  the  body  we  shall  first  discuss  the  structure  and  development  of 
the  cell. 

THE   STRUCTURE    OF  THE    CELL. 

The  typical  tissue  cell  is  a  spherical  or  ovoid  mass  of  protoplasm.  Its 
structure  is  quite  complex,  but  the  most  general  differentiation  is  into  the  cell 
mass  or  cytoplasm,  and  its  contained  nucleus.  The  cytoplasm  is  sometimes 
bounded  by  a  definite  cell  membrane,  but  in  differentiated  animal  tissues  this 
membrane  is  usually  not  present. 

The  Cell  Body.  The  cell  body  or  cytoplasm  is  a  complex  semi- 
fluid mass,  the  detailed  structure  of  which  has  presented  problems  of  many 
difficulties.  It  is  usually  described  as  having  a  framework  of  spongioplasm  or 
formed  elements,  and  a  homogeneous  hyaloplasm.  In  some,  cells  there  are 
formed  materials  resulting  from  the  cellular  activity  called  meta plasm,  figure 
14.  These  structural  features  are  made  more  evident  by  their  affinity  for 
certain  staining  reagents. 

The  spongioplasm  or  reticulum  varies  greatly  in  different  types  of  cells, 
and  even  in  different  parts  of  the  same  cell.  It  has  considerable  affinity  for 
stains  which  exhibit  a  fine  network,  the  reticulum.  It  increases  in  amount 
in  older  cells  and  also  in  constancy  in  the  type  of  arrangement. 

•  The  hyaloplasm  is  more  fluid,  less  refractile,  and  stains  with  great  difficulty. 
It  fills  the  interspaces  of  the  spongioplasm.  In  this  material  may  be  embedded 
such  substances  as  the  metaplasts  mentioned  above. 

Structure  of  the  Nucleus.  The  nucleus  when  in  a  condition  of  rest 
is  bounded  by  a  distinct  membrane,  the  nuclear  membrane,  possibly  derived 
from  the  spongioplasm  of  the  cell,  which  encloses  the  nuclear  contents,  nucleo- 
plasm or  karyoplasm.  The  membrane  consists  of  an  inner,  or  chromatic,  and 
of  an  outer,  or  achromatic  layer,  so  called  from  their  reaction  to  stains.  The 
nucleoplasm  is  made  up  of  a  reticular  network,  or  chromoplasm,  whose  inter- 
spaces are  filled  by  the  karyolymph,  or  nuclear  matrix,  a  homogeneous  sub- 
2  17 


18 


CELL    DIFFERENTIATION    AND    THE     ELEMENTARY    TISSUES 


stance  which  is  rich  in  proteids,  has  but  slight  affinity  for  stains,  and  is  supposed 
to  be  fluid. 

The  network  is  composed  of  linin  or  achromatin,  a  transparent  unstainable 
framework;  and  of  chromatin,  which  stains  deeply.  It  is  supported  by  the 
linin,  and  occurs  sometimes  in  the  form  of  granules,  but  usually  as  irregular 
anastomosing  threads,  both  thicker  primary  fibers  and  thinner  connecting 
branches.  The  threads  often  form  thickened  nodes,  karyosomes  or  false 
nucleoli,  at  their  points  of  intersection.     It  is  now  quite  generally  believed  that 


Cell  membrane. 


Metaplasm      gran- 
ules. 


Karyosome  or  net- 
knob. 

Hyaloplasm. 
Spongioplasm. 

Linin  network. 
Nucleoplasm. 


Attraction  sphere. 
Centrosome. 

Plastids. 


Chromatin  network 
Nuclear  membrane. 


'— -  Nucleolus. 


....  Vacuole. 


Fig.  14. — Diagram  of  a  Typical  Cell.     (Bailey.) 


the  chromatin  occurs  as  short,  rodlike,  and  highly  refractive  masses,  which  are 
embedded  in  the  linin  in  a  regular  series. 

The  nucleoli,  or  plasmosomes,  are  spherical  bodies  which  stain  deeply,  and 
may  either  lie  free  in  the  nuclear  matrix  or  be  attached  to  the  threads  of  the  net- 
work. 

The  Centrosome  and  Attraction  Sphere.  In  addition  to  the  nucleus, 
a  minute  spherical  body  called  the  centrosome  is  believed  to  be  constantly 
present  in  animal  cells,  though  sometimes  too  small  to  be  demonstrated. 
The  centrosome  is  smaller  than  the  nucleus,  close  to  which  it  lies,  and  exerts  a 
peculiar  attraction  for  the  protoplasmic  filaments  and  granules  in  its  vicinity, 
so  that  it  is  surrounded  by  a  zone  of  fine  radiating  fibrils,  forming  the  attraction 
sphere  or  archoplasm.  Some  authorities  assert  that  the  centrosome  lies  within 
the  nucleus  in  the  resting  state,  and  passes  into  the  cell  proper  only  in  the  earlier 
stages  of  cell  division.  The  attraction  sphere  is  most  distinctly  seen  in  cells 
about  to  divide.  It  plays  an  important  role  in  nuclear  division,  but  it  is 
doubted  if  it  gives  the  initial  impulse  to  the  process. 

Cell  Multiplication.  Cells  increase  in  number  by  a  process  known 
as  cell  division,  of  which  the  first  act  is  nuclear  division.  In  fact  the  nucleus  is 
the  center  of  control  of  the  cell-mass  in  the  process  of  division.     Cell  muki- 


CELL    MULTIPLICATION 


19 


plication  takes  place  by  two  recognized  methods,  direct  (amitosis),  in  which 
there  is  little  disturbance  of  the  nuclear  network,  and  indirect  (mitosis),  in 
which  there  is  a  complex  series  of  nuclear  network  changes.     These  mitotic 
changes  result  in   the   division  of  the  chromatin   fila- 
ments into  the  two  new  parts  which  form  the  chromo- 
plasm  of  the  daughter  nuclei. 

The   process    may   be   divided    into    the    following 
stages : — 

Prophase.  The  resting  nucleus  becomes  somewhat 
enlarged,  and  the  centrosome  (according  to  those  who 
regard  it  as  lying  normally  within  the  nucleus)  migrates 
into  the  cell  protoplasm.  The  centrosome  then  divides 
into  two  daughter  centrosomes  which  lie  near  the  nucleus 
but  are  separated  by  a  considerable  interval.  Each  is 
surrounded  by  the  radiating  fibrils  of  the  attraction 
sphere,  and  some  of  these  fibrils  pass  continuously  from 
one  centrosome  to  the  other,  forming  the  achromatic 
spindle.  At  the  same  time  the  intranuclear  network  be- 
comes converted  into  a  fine  convoluted  coil  (spirem  or 
skein)  which  may  be  either  continuous  or  else  broken  up  into  several  threads. 
The  thread  or  threads  then  shorten  and  become  thicker,  while  the  convolutions, 
which  have  become  less  numerous,  arrange  themselves  in  a  series  of  con- 
necting loops,  forming  the  wreath.  The  nuclear  membrane  and  the  nucleolus 
disappear,  the  latter  passing  at  times  into  the  cell  protoplasm  and  disintegrat- 
ing. The  wreath  then  breaks  up  into  V-shaped  segments,  the  chromosomes, 
of  which  each  species  of  animal  has  a  constant  and  characteristic  number. 
This  varies  in  the  different  animals,  but  is  sixteen  in  man. 

The  two  centrosomes  migrate  to  the  poles  of  the  nucleus,  while  the  achro- 
matic spindle  which  connects  them  occupies  the  long  axis  of  the  nucleus.     The 

A  B 


Fig.  is  — Leucocyte 
of  Salamander  Larva, 
Showing  Attraction 
Sphere.  (After  Flem- 
ming.) 


Fig.  16. — Early  Stages  of  Karyokinesis.  A.  The  thicker  primary  fibers  remain  and  the  achro- 
matic spindle  appears.  B.  The  thick  fibers  split  into  two  and  the  achromatic  spindle  becomes 
longitudinal.      (Waldeyer.) 

chromosomes,  becoming  much  shorter  and  thicker,  gather  around  the  spindle 
in  its  equatorial  plane,  with  their  angles  directed  toward  the  center,  forming 
the  aster  or  monaster. 

Metaphase.  The  actual  division  of  the  nucleus  is  begun  at  this  time  by  the 
splitting  of  each  chromosome  longitudinally  into  halves  which  lie  at  first  close 


20 


CELL    DIFFERENTIATION    AND     THE     ELEMENTARY    TISSUES 


together  so  that  each  seems  doubled.  Soon  afterward  the  fibrils  of  the  achro- 
matic spindle  begin  to  contract,  and  thus  separate  the  halves  of  the  chromosomes 
in  such  a  way  that  one-half  of  each  is  turned  toward  one  pole,  and  the  other 
half  toward  the  other.     As  this  continues,  the  two  groups,  which  are  equal  in 


central 


dear  area 
of  nucleus- *" 


jPolar  rruZiattOnr 
ST"  (CyUtsCer) 

'  \    atti  vocllon,  sjikere' 

|«j       chrorruxUni 
"jii'S     lonaUuclinaZZy 


,./X?l  suistcavec 
Polar mdicUiiaitf 


jxtrUda 
Fig.  17. — Monaster  Stage  of  Karyokinesis.     (Rabl.) 

size,  draw  away  from  each  other  and  from  the  equator,  each  group  being 
formed  of  daughter  chromosomes. 

Anaphase.  The  two  groups  (daughter  chromosomes)  now  gradually  ap- 
proach their  respective  poles,  or  centrosomes,  and  the  equator  becomes  free. 
On  reaching  the  pole,  each  group  gathers  in  a  form  which  is  similar  in  arrange- 
ment to  the  monaster  and  is  known  as  the  diaster.  During  this  time  the  cell 
body  becomes  slightly  constricted  by  a  circular  groove  at  its  equatorial  plane. 

Telophase.  Soon  afterward  the  fibrils  of  the  chromatic  spindle  which 
connect  the  two  groups  begin  to  grow  dim  and  finally  disappear.     The  daugh- 


W 


Fig.  18 — Stages  of  Karyokinesis.  (Rabl.)  A.  Commencing  separation  of  the  split  chromo- 
somes. B.  The  separation  further  advanced.  C.  The  separated  chromosomes  passing  along 
the  fibers  of  the  achromatic  spindle. 

ter  chromosomes  assume  the  form  of  threads  twisted  in  a  coil  and  develop 
each  a  nuclear  membrane  and  a  nucleolus,  forming  a  daughter  nucleus.  The 
nuclei  enlarge  and  the  nuclear  threads  assume  the  appearance  of  the  resting 
state  of  the  nucleus.  Meanwhile,  the  constriction  about  the  body  of  the  cell 
has  become  deeper  and  deeper  until  the  protoplasm  is  divided  into  two  equal 
parts,  or  daughter  cells,  each  with  its  daughter  nucleus,  and  the  process  of 
karyokinesis  is  completed. 


MODES     OF    CELL    CONNECTION 


21 


The  Cell  Types.  All  of  the  elementary  tissues  consist  of  cells  and 
of  their  altered  equivalents.  It  will  be  as  well  therefore  to  indicate  some  of  the 
differences  between  the  cells  of  the  body.  They  are  named  in  various  ways, 
according  to  their  shape,  origin,  and  functions. 

From  their  shape,  cells  are  described  as  spherical  or  spheroidal,  which  is  the 
typical  shape  of  the  free  cell;  this  may  be  altered  to  polyhedral  when  the  pres- 
sure on  a  mass  of  cells  in  all  directions  is  nearly  the  same;  of  this  the  primitive 
segmentation  cells  afford  an  example.  The  discoid  form  is  seen  in  blood- 
corpuscles,  and  the  scale-like  form  in  superficial  epithelial  cells.  Some  cells 
have  a  jagged  outline  and  are  then  called  prickle  cells.  Cells  of  cylindrical, 
conical,  or  prismatic  form  occur  in  various  places  in  the  body.  Such  cells  may 
taper  at  one  or  both  ends  into  fine  processes,  in  the  former  case  being  caudate, 
in  the  latter  jusijorm.     They  may  be  greatly  elongated  so  as  to  become  fibers. 


—  Remains  of  spindle. 

>  Lighter  substance 
of  nucleus. 

S Cell  protoplasm. 

Hilus. 


Line  of  division 
of  cells. 
Antipole  of  daughter  -- 
nucleus. 


Fig.  19. — Final  Stages  of  Karyo kinesis.     In  the  lower  figure  the  changes  are  still  more  ad- 
vanced than  in  the  upper.     (Waldeyer.) 


Cells  with  hair-like  processes,  or  cilia,  projecting  from  their  free  surfaces,  are 
a  special  variety.  The  cilia  vary  greatly  in  size,  and  may  even  exceed  in  length 
the  cell  itself.  Finally,  cells  may  be  branched  or  stellate  with  long  outstanding 
processes. 

From  their  junction  cells  are  called  secreting,  protective,  sensitive,  contractile, 
and  the  like. 

From  their  origin  ceils  are  called  epiblastic  and  mesoblastic  and  hypoblastic 
(ectodermic,  mesodermic,  and  endodermic). 

Modes  of  Cell  Connection.  Cells  are  connected  together  to  form 
tissues  in  various  ways. 

They  are  connected  by  means  of  a  cementing  intercellular  substance.  This 
is  probably  always  present  as  a  transparent,  colorless,  viscid,  albuminous 
substance,  even  between  the  closely  apposed  cells  of  epithelium;  while  in 
the  case  of  cartilage  it  forms  the  main  bulk  of  the  tissue,  and  the  cells  only 
appear  as  embedded  in,  not  as  cemented  together  by,  the  intercellular  substance. 
This  intercellular  substance  may  be  either  homogeneous  or  fibrillated.  In 
many  cases,  e.g.,  the  cornea,  it  can  be  shown  to  contain  a  number  of  irregular 
branched  cavities,  which  communicate  with  each  other,  and  in  which  branched 


22  CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 

cells  lie.  Nutritive  fluids  can  find  their  way  through  these  branching  spaces 
into  the  very  remotest  parts  of  a  non-vascular  tissue.  The  basement  mem- 
brane (membrana  propria)  must  be  mentioned  as  a  special  variety  of  intercellu- 
lar substance  which  is  found  at  the  base  of  the  epithelial  cells  in  most  mucous 
membranes,  and  especially  as  an  investing  tunic  of  gland  follicles  which  deter- 
mines their  shape. 

Cells  are  connected  by  anastomosis  of  their  processes.  This  is  the  usual 
way  in  which  stellate  cells,  e.g.,  of  the  cornea,  are  united.  The  individuality 
of  each  cell  is  thus  to  a  great  extent  lost  by  its  connection  with  its  neighbors  to 
form  a  reticulum.  As  an  example  of  a  network  so  produced  we  may  cite 
the  anastomosing  cells  of  the  reticular  tissue  of  lymphatic  glands. 

Derived  Elements.  Besides  the  cell,  which  may  be  termed  the 
primary  tissue  element,  there  are  materials  which  may  be  termed  secondary 
or  derived  elements  or  formed  materials.  Examples  of  this  type  of  structure 
are  found  in  the  matrix  of  cartilage,  the  fibers  of  connective  tissue,  bone,  etc. 

Decay  and  Death  of  Cells.  There  are  two  chief  ways  in  which  the 
comparatively  brief  existence  of  cells  is  brought  to  an  end,  by  mechanical  abra- 
sion and  by  chemical  transformation. 

The  various  epithelia  furnish  abundant  examples  of  mechanical  abrasion. 
As  it  approaches  the  free  surface,  the  cell  becomes  more  and  more  flattened  and 
scaly  in  form  and  more  horny  in  consistency,  till  at  length  it  is  simply  rubbed 
off  as  in  the  epidermis.  Hence  we  find  free  epithelial  cells  in  the  mucus  of 
the  mouth,  intestine,  and  in  the  genito-urinary  tract. 

In  the  case  of  chemical  transformation  the  cell-contents  undergo  a  degener- 
ation which,  though  it  may  sometimes  be  pathological,  is  very  often  a  normal 
process.  Thus  we  have  cells  by  fatty  metamorphosis  producing  oil-globules 
in  the  secretion  of  milk,  fatty  degeneration  of  the  muscular  fibers  of  the  uterus 
after  the  birth  of  the  fetus.  Calcareous  degeneration  is  common  in  the  cells  of 
many  cartilages. 

THE  STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 

There  are  certain  elementary  structures  formed  in  the  process  of  differentia- 
tion which  alone  or  when  combined  in  varying  proportions  form  the  whole 
of  the  organs  and  tissues  of  the  body.  These  elementary  tissues  are:  The 
Epithelial,  The  Connective,  The  Muscular,  and  The  Nervous  Tissues.  To 
these  four  some  would  add  a  fifth,  looking  upon  the  Blood  and  Lymph,  con- 
taining, as  they  do,  formed  elements  in  a  fluid  menstruum,  as  a  distinct  tissue. 

I.  THE  EPITHELIAL  TISSUES. 

Epithelium  is  a  tissue  composed  almost  wholly  of  cells,  with  a  very  small 
amount  of  intercellular  substance  which  glues  the  cells  together.  In  general 
it  includes  all  those  cellular  membranes  which  cover  either  an  external  or 


CLASSIFICATION     OF    EPITHELIA  23 

an  internal  free  surface,  together  with  the  cellular  portions  of  the  glands  which 
are  connected  with,  or  developed  from,  these  free  surfaces. 

Epithelium  clothes  (i)  the  whole  exterior  surface  of  the  body,  forming 
the  epidermis  with  its  appendages;  becoming  continuous  at  the  chief  orifices 
of  the  body — nose,  mouth,  anus,  and  urethra — with  (2)  the  epithelium  which 
lines  the  whole  length  of  the  respiratory,  alimentary,  and  genito-urinary 
tracts,  together  with  the  ducts  and  secretory  cells  of  their  various  glands. 
Epithelium  also  lines  the  cavities  of  (3)  the  brain  and  the  central  canal  of  the 
spinal  cord,  (4)  the  serous  and  synovial  membranes,  and  (5)  the  interior  of 
blood-vessels  and  lymphatics. 

Epithelial  cells  vary  in  size  and  shape,  pressure  being  the  main  factor  in  this 
variation.  The  protoplasm  may  be  granular,  reticular,  or  fibrillar  in  appear- 
ance. The  nucleus  is  spherical  or  oval,  usually  there  is  only  one,  but 
there  may  be  two  or  more,  present. 

Epithelial  tissues  are  non-vascular,  that  is  to  say,  do  not  contain  blood- 
vessels, but  in  some  varieties  minute  channels  exist  between  the  cells  of  certain 
layers.     Nerve  fibers  are  supplied  to  the  cells  of  many  epithelia. 

CLASSIFICATION    OF    EPITHELIA. 

As  to  form  and  arrangement  of  cells. 

I.   Epithelia  in  the  form  of  membranes  (covering  surfaces). 

1.  Simple  epithelium.     Cells  only  one  layer  in  thickness. 

(1)  Squamous  or  pavement.     Cells  flattened. 

(a)  Non-ciliated.  Alveoli  of  lungs,  also  includes  endothelium, 
lining  the  blood-vessels,  and  mesothelium,  lining  the  large 
serous  spaces. 

(b)  Ciliated.     The  peritoneum  of  some  forms  at  breeding  season. 

(2)  Cubical  epithelia.       Cells    with    the  three   dimensions    approxi- 

mately equal,  mainly  glandular. 

(a)  Non-ciliated.  The  usual  type.  It  is  found  lining  both 
ducts  and  secretory  portions  of  most  glands,  the  pigmented 
layer  of  the  retina,  etc. 

(b)  Ciliated.  Not  common.  Lining  of  some  of  the  smaller 
bronchial  tubes. 

(3)  Columnar.     Cells  may  be  cylindrical,  conical,  or  goblet  shaped. 

(a)  Non-ciliated.     Intestinal. 

(b)  Ciliated.     Fallopian  tube  and  uterus. 

(c)  Pseudo-stratified.     Smaller  bronchi,  nasal  duct,  etc. 

2.  Stratified  epithelia.     Cells  more  than  one  layer  in  thickness. 
(1)  Squamous.     Surface  cells  flattened. 

(a)  Non-ciliated.     Skin,  mouth,  vagina,  etc. 

(b)  Ciliated.     Pharynx  of  embryo. 


24  CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 

(2)  Columnar.     Surface  cells  columnar. 

(a)  Non-ciliated.     Portions  of  male  urethra. 

(b)  Ciliated.     Trachea,  bronchi,  etc. 

II.  Epithelia  not  in  the  form  of  membranes,  but  in  solid  masses  or  cords, 
usually  glandular. 

(1)  Cells  spheroidal,  ova. 

(2)  Cells  polyhedral,  liver,  suprarenal,  etc. 

Epithelia,  classified  mainly  as  to  function. 

I.  Protective.     Skin,  mouth,  alimentary  canal. 

1.  Cornified.     Skin,  nails,  hair. 

2.  Cuticular  border.     Columnar  cells  of  intestine. 

II.  Glandular. 

1.  Secretory.     Cells  of  salivary  glands,  pancreas,  etc. 

2.  Execretory.     Cells  of  kidney. 

3.  Absorptive.     Cells  of  alimentary  canal. 

III.  Sensory  Epithelium.     Cells  of  olfactory  membrane,  organ  of  Corti, 

taste  buds,  etc. 

IV.  Reproductive.     Sex  cells. 

V.  Pigmented.     Pigmented  layer  of  retina. 
VI.   Ciliated.     Trachea,  uterus,  Fallopian  tube,  etc. 

Only  a  few  of  the  more  important  of  the  above-mentioned  types  of  epithe- 
lium will  be  described  here. 

Simple  Epithelium.  Simple  Squamous.  This  form  of  epithelium 
is  found  arranged  in  a  single  layer  of  flattened  cells,  for  example,  the  lining  of 
the  alveoli  of  the  lungs  and  of  the  descending  arm  of  Henle's  loop  of  the  kidney 
tubule.  Aside  from  endothelium  as  mesothelium  it  has  very  limited  dis- 
tribution in  man.     Endothelium  and  mesothelium  are  typical  simple  squamous 


Fig.  20. — The  Endothelium  of  a  Small  Blood-vessel.     Silver-nitrate  stain.      X  35°. 

epithelia.  They  consist  of  much  flattened  cells  with  clear  or  slightly  granular 
protoplasm  and  oval  bulging  nuclei,  the  edges  of  the  cells  are  peculiarly  wavy 
or  serrated. 

The  presence  of  endothelium  in  any  locality  may  be  demonstrated  by  stain- 
ing with  silver  nitrate,  which  brings  into  view  the  intercellular  cement  sub- 


SIMPLE     EPITHELIUM 


25 


stance.  When  a  small  portion  of  a  perfectly  fresh  serous  membrane,  for 
example,  figure  20,  is  immersed  for  a  few  minutes  in  a  solution  of  silver 
nitrate,  and  exposed  to  the  action  of  light,  the  silver  is  precipitated  in  the  in- 


Fig.  a  1. — Abdominal  Surface  of  Central  Tendon  of  the  Diaphragm  of 'Rabbit,  showing  the 
general  polygonal  shape  of  the  endothelial  cells;   each  cell  is  nucleated.      (Klein.)      X  300. 

tercellular  cement  substance,  and  the  endothelial  cells  are  thus  mapped  out  by 
fine,  dark,  and  generally  sinuous  lines  of  extreme  delicacy. 

Endothelial  cells  in  certain  situations  may  be  ciliated,  e.g.,  those  of  the 
mesentery  of  the  frog,  especially  during  the  breeding  season. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes  in 
which  lymphatics  abound,  apertures,  figure  22,  are  found  surrounded  by  small, 
more  or  less  cubical,  cells.  These  apertures  are  called  stomata.  They  are 
particularly  well  seen  in  the  anterior  wall  of  the  great  lymph  sac  of  the  frog, 


Pig.  22. — Peritoneal  Surface  of  a  Portion  ot  the  Septum  of  the  great  Lymph-Sac  of  Frog. 
The  stomata,  some  of  which  are  open,  some  collapsed,  are  surrounded  by  endothelial  cells.  (Klein.) 
X160. 


figure  22,  and  in  the  omentum  of  the  rabbit.  These  are  really  the  open  mouths 
of  lymphatic  vessels  or  spaces,  and  through  them  lymph-corpuscles  and  the 
serous  fluid  from  the  serous  cavity  pass  into  the  lymphatic  system. 

Simple  N on-Ciliated  Columnar  Epithelium,  figure  23,  lines,  a,  the  mucous 
membrane  of  the  stomach  and  intestines  as  a  single  layer,  from  the  cardiac 


26 


CELL     DIFFERENTIATION     AND     THE    ELEMENTARY    TISSUES 


orifice  of  the  stomach  to  the  anus,  and  b,  wholly  or  in  part  all  the  ducts  of  the 
glands  opening  on  its  free  surface,  and  c,  many  gland-ducts  in  other  regions 
of  the  body,  e.g.,  mammary,  salivary,  etc.  The  intracellular  and  intranuclear 
networks  are  well  developed,  and  in  some  cases  the  spongioplasm  is  arranged 


Fig.  23. — Simple  Columnar  Ephithelial  Cells  from  the  Human  Intestinal  Mucous  Membrane, 
o.  Mucous  (goblet)  cell;  b,  basement  membrane;  c,  cuticle;  d,  leucocyte  nucleus;  e,  germinating 
cell.      (Bailey.) 

in  rods  or  longitudinal  striae  at  one  part  of  the  cell,  as  in  the  cells  of  the  ducts 
of  salivary  glands.  The  protoplasm  of  columnar  cells  may  be  vacuolated 
and  may  also  contain  fat  or  other  substances  seen  in  the  form  of  granules. 
Certain  columnar  cells  transform  a  large  part  of  their  protoplasm  into  mucin, 
goblet  cells,  figure  24,  which  isdischarged  by  the  open  mouth  of  the  goblet,  leav- 


Fig.  24. 


Fig.  25. 


Fig.  24. — Goblet  Cells.     (Klein.) 

Fig.  25. — Cross-section  of  a  Villus  of  the  Intestine,  e,  Columnar  epithelium  with  striated 
border;  g,  goblet  cell,  with  its  mucus  partly  extruded;  /.  lymph-corpuscles  between  the  epithelial 
cells;  b,  basement  membrane;  c,  sections  of  blood-capillaries;  m,  section  of  plain  muscle  fibers; 
c.l,  central  lacteal.     (Schafer.) 

ing  only  a  nucleus  surrounded  by  the  remains  of  the  protoplasm  in  its  narrow 
stem.  This  transformation  is  a  normal  process  which  is  continually  going  on 
during  life,  the  cells  themselves  being  supposed  to  regenerate  into  their  original 
shape. 


STRATIFIED     EPITHELIUM 


27 


Stratified  Epithelium.  The  term  stratified  epithelium  is  employed 
to  describe  the  type  found  in  the  skin  or  its  derivatives  in  which  the  cells 
forming  the  epithelium  are  arranged  in  a  considerable  number  of  superim- 
posed layers.  The  shape  and  size  of  the  cells  of  the  different  layers,  as  well 
as  the  number  of  layers,  vary  in  different  situations.  Thus  the  superficial  cells 
may  be  either  squamous  or  columnar  in  shape  and  the  deeper  cells  range 
from  polygonal  to  columnar  in  form. 

Stratified  Squamous.  The  intermediate  cells  are  polygonal  in  shape  and 
approach  more  to  the  flat  variety  the  nearer  they  are  to  the  surface,  and  to  the 


Fig.  26. — Squamous  Epithelium  Scales  from  the  Inside  of  the  Mouth.      X  260.      (Henle.) 

columnar  as  they  approach  the  lowest  layer.  In  many  of  the  deeper  layers 
of  epithelium  in  the  mouth  and  skin,  the  outline  of  the  cells  is  very  irregular, 
in  consequence  of  processes  passing  from  cell  to  cell  across  these  intervals. 
Such  cells,  figure  28,  are  termed  "  prickle"  cells.  These  "  prickles"  are  the  in- 
tercellular bridges  which  run  across  from  cell  to  cell,  the  interstices  being  filled 
by  the  transparent  intercellular   lymph.     When   this   increases   in  quantity 


wmL^w 


Fig.  27. — Vertical  Section  of  the  Stratified  Epithelium  Covering  the  Front  of  the  Cornea.  Highly 
magnified.  (Schafer.)  c.  Lowermost  columnar  cells;  p,  polygonal  cells  above  these;  fl,  flat- 
tened cells  near  the  surface.  The  intercellular  channels,  bridged  by  minute  cell  processes,  are 
well  seen. 

in  inflammation  the  cells  are  pushed  further  apart,  and  the  connecting  fibrils 
or  "  prickles"  are  elongated  and  more  clearly  visible. 

The  columnar  cells  of  the  deepest  layer  are  distinctly  nucleated;  they 
multiply  rapidly  by  division;  and  as  new  cells  are  formed  beneath,  they  press 
the  older  cells  forward,  to  be  in  turn  pressed  forward  themselves  toward  the  sur- 
face, gradually  altering  in  shape  and  chemical  composition  until  they  die  and 
are  cast  off  from  the  surface. 


28 


CELL     DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


Stratified  squamous  epithelium  is  found  in  the  following  situations:  i. 
Forming  the  epidermis,  covering  the  whole  of  the  external  surface  of  the  body; 
2.  Covering  the  mucous  membrane  of  the  nose,  tongue,  mouth,  pharynx,  and 
esophagus;  3.  As  the  conjunctival  epithelium,  covering  the  cornea;  4.  Lining 
the  vagina  and  the  vaginal  part  of  the  cervix  uteri. 

Stratified  Columnar  Epithelium.  In  this  type  of  epithelium,  the  surface 
cells  alone  are  columnar,  the  deeper  cells  being  irregular  in  shape      From 


<m 


Fig.  28. — Epithelial  Cells  from  the  Stratum  Spinosum  of  the  Human  Epidermis,  Showing 
"Intercellular  Bridges."    X   700.      (Szymonowicz.) 

the  surface  cells  long  processes  extend  down  among  the  underlying  cells. 
This  type  of  epithelium  is  usually  ciliated,  as  in  the  trachea,  bronchi,  etc., 
but  may  be  non-ciliated,  as  in  portions  of  the  human  male  urethra. 

Transitional  Epithelium.     This  is  a  stratified  epithelium  consisting  of  only 
three  or  four  layers  of  cells.     The  superficial  cells  are  large  and  flat,  often 


Fig.  29. — Stratified  Columnar  Ciliated  Epithelium  from  the  Human  Trachea.     A  mucous 
(goblet)  cell  also  is  present. 

containing  two  nuclei.  The  under  surfaces  of  these  cells  are  hollowed  out,  and 
into  these  depressions  fit  the  large  ends  of  the  pyriform  cells  which  form  the 
next  layer.  Beneath  the  layer  of  pyriform  cells  are  from  one  to  four  layers 
of  polyhedral  cells.  This  type  of  epithelium  occurs  in  the  bladder,  ureter, 
and  pelvis  of  the  kidney. 


STRATIFIED    EPITHELIUM 


29 


Specialized  Epithelium.  Glandular  Epithelium  forms  the  active  secreting 
agent  in  the  glands;  the  cells  are  usually  spheroidal,  but  may  be  polyhedral 
from  mutual  pressure,  or  even  columnar;  their  protoplasm  is  generally  oc- 
cupied by  the  materials  which  the  gland  secretes.     Examples  of  glandular 


©; 


m 


M 

Fig.  30. — Transitional  Epithelium  from  the  Human  Bladder.      (Bailey.) 

epithelium  are  to  be  found  in  the  liver,  figure  31,  in  the  secreting  tubes  of 
the  kidney,  and  in  the  salivary,  figure  32,  and  gastric  glands. 

Ciliated  epithelium  consists  of  cells  which  are  generally  cylindrical  in  form, 
figures  29,  30,  but  may  be  spheroidal  or  even  squamous. 

This  form  of  epithelium  lines:  a.  The  mucous  membrane  of  the  respiratory 
tract  beginning  just  beyond  the  nasal  aperture,  and  completely  covers  the  nasal 
passages,  except  the  upper,  part  to  which  the  olfactory  nerve  is  distributed, 


Fig. 


Fig.  32. 


Fig.  31. — A  Small  Piece  of  the  Liver  of  the  Horse.      (Cadiat.) 

Fig.  32. — Glandular  Epithelium.     Small  lobule  of  a  mucous  gland  of  the  tongue,  showing 
nucleated  glandular  cells.      X  200.      (V.  D.  Harris.) 

and  also  the  sinuses  and  ducts  in  connection  with  it  and  the  lachrymal  sac, 
the  upper  surface  of  the  soft  palate  and  the  naso-pharynx,  the  Eustachian  tube 
and  tympanum,  the  larynx,  except  over  the  vocal  cords,  to  the  finest  sub- 
divisions of  the  bronchi.  In  part  of  this  tract,  however,  the  epithelium  is  in 
several  layers,  of  which  only  the  most  superficial  is  ciliated,  so  that  it  should 


30 


CELL     DIFFERENTIATION     AND     THE     ELEMENTARY     TISSUES 


more  accurately  be  termed  transitional,  page  28,  or  stratified,  b.  Some  portions 
of  the  generative  apparatus  in  the  male,  viz.,  lining  the  "vasa  efferentia"  of 
the  testicle,  and  their  prolongations  as  far  as  the  lower  end  of  the  epididymis, 
and  much  of  the  vas  deferens;  in  the  female,  c,  commencing  about  the  middle 


Fig.  33. — Specialized  Pigmented  Epithelial  Cells  of  Retina. 

of  the  neck  of  the  uterus,  and  extending  throughout  the  uterus  and  Fallopian 
tubes  to  their  fimbriated  extremities,  and  even  for  a  short  distance  on  the  per- 
itoneal surface  of  the  latter,  d.  The  ventricles  of  the  brain  and  the  central 
canal  of  the  spinal  cord  are  clothed  with  ciliated  epithelium  in  the  child,  but 
in  the  adult  this  epithelium  is  limited  to  the  central  canal  of  the  cord. 


Fig.  34. 


Fig.  35. 


Fig.  34. — Spheroidal  Ciliated  Cells  from  the  Mouth  of  the  Frog.      X  300  diameters.   (Sharpey.) 
Fig.  35. — Ciliated   Epithelium  from  the   Human  Trachea,     a.   Large,  fully  formed  cell,     b, 
shorter  cell;    c,  developing  cells  with  more  than  one  nucleus.      (Cadiat.) 


The  cilia  themselves  are  fine  rounded  or  flattened  homogeneous  processes. 
According  to  some  observers  these  processes  are  connected  with  longitudinal 
fibers  which  pass  to  the  other  end  of  the  cell,  but  which  are  not  connected  with 
the  nucleus. 


THE     CONNECTIVE     TISSUES 


31 


Functions  of  Epithelium.  According  to  function, 
epithelial  cells  may  be  classified  as:  i,  protective,  e.g.,  in 
the  skin,  mouth,  blood-vessels,  etc.;  2,  protective  and  mo- 
tive, ciliated  epithelium;  3,  secreting,  glandular  epithelium; 
4,  germinal,  as  epithelium  of  testicle  producing  sperma- 
tozoa; 5,  absorbing  and  secreting,  e.g.,  epithelium  of  intes- 
tine; 6,  sensory,  e.g.,  olfactory  cells,  organ  of  Corti. 

Epithelium  forms  a  continuous  smooth  investment 
over  the  whole  body,  being  thickened  into  a  hard,  horny 
tissue  at  the  points  most  exposed  to  pressure,  and  develop- 
ing various  appendages,  such  as  hairs  and  nails.  Epi- 
thelium lines  also  the  sensorial  surfaces  cf  the  eye,  ear,' 
nose,  and  mouth,  and  thus  serves  as  the  medium  through 
which  all  impressions  from  the  external  world — touch, 
smell,  taste,  sight,  hearing — reach  the  delicate  nerve  end- 
ings, whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages 
serves  to  promote  currents  of  the  air  in  the  bronchial  tubes 
and  to  propel  fluids  and  minute  particles  of  solid  matter  out 
of  the  body.  In  the  case  of  the  Fallopian  tube,  the  cilia 
assist  the  progress  of  the  ovum  toward  the  cavity  of  the 
uterus. 

The  epithelium  of  the  various  glands,  and  of  the 
whole  intestinal  tract,  has  the  power  of  secretion,  i.e.,  of 
producing  certain  materials  by  processes  of  metabolism  in  its  protoplasm. 

Epithelium  is  likewise  concerned  in  the  processes  of  transudation,  diffusion, 
and  absorption. 


Fig.  36. — Ciliated 
Cell  of  the  Intestine 
of  a  Mollusk.  (En- 
gelmann.) 


II.    THE   CONNECTIVE  TISSUES. 


This  group  of  tissues  forms  the  skeleton  with  its  various  connections — 
bones,  cartilages,  and  ligaments — and  also  affords  a  supporting  framework 
and  investment  to  the  various  organs  composed  of  nervous,  muscular,  and  glan- 
dular tissue.  Its  chief  function  is  the  mechanical  one  of  support,  and  for 
this  purpose  it  is  so  intimately  interwoven  with  nearly  all  the  textures  of  the 
body  that  if  all  other  tissues  could  be  removed,  and  the  connective  tissues  left, 
we  should  have  a  wonderfully  exact  model  of  almost  every  organ  and  tissue  in 
the  body. 

General  Structure  of  Connective  Tissue.  The  connective  tissue  is 
made  up  of  two  chief  elements,  namely,  cells  and  intercellular  or  formed  sub- 
stance. 

Cells.  The  cells  are  usually  of  an  oval  shape,  often  with  branched 
processes,  which  are  united  to   form   a   network.      They  are  most  readily 


32  CELL     DIFFERENTIATION    AND     THE     CONNECTIVE     TISSUES 

observed  in  the  cornea,  in  which  they  are  arranged,  layer  above  layer,  parallel 
to  the  free  surface.  They  lie  in  spaces  in  the  intercellular  or  ground  substance, 
which  form  by  anastomosis  a  system  of  branching  canals  freely  communicating, 
figure  37. 

The  flattened  tendon  corpuscles  which  are  arranged  in  long  lines  or  rows 
parallel  to  the  fibers  belong  to  this  class  of  cells,  figure  39. 

These  branched  cells  often  contain  pigment  granules,  giving  them  a  dark 
appearance;    they  form  one  variety  of  pigment  cell.     Pigment  cells  of  this 


Fig.  37. — Horizontal  Preparation  of  the  Cornea  of  Frog,  Stained  in  Gold  Chloride;  showing 
the  network  of  branched  corneal  corpuscles.  The  ground  substance  is  completely  colorless. 
X  400.     (Klein.) 

kind  are  found  in  the  outer  layers  of  the  choroid.  In  many  of  the  lower  ani- 
mals, such  as  the  frog,  they  are  found  widely  distributed  not  only  in  the  skin, 
but  also  in  internal  parts,  the  mesentery,  sheaths  of  blood-vessels,  etc.  Under 
the  action  of  light,  electricity,  and  other  stimuli,  the  pigment  granules  become 
massed  in  the  body  of  the  cell,  leaving  the  processes  quite  hyaline;  if  the 
stimulus  be  removed,  they  will  gradually  be  distributed  again  throughout  the 
processes.  Thus  the  skin  in  the  frog  is  sometimes  uniformly  dusky,  and  some- 
times quite  light-colored,  with  isolated  dark  spots. 

Intercellular  Substance.  This  is  fibrillar,  as  in  the  fibrous  tissues  and  in 
certain  varieties  of  cartilage;  or  homogeneous,  as  in  typical  mucoid  tissue. 

The  fibers  composing  the  former  are  of  two  kinds,  white  fibrous  and  yellow 
elastic  tissue. 

The  chief  varieties  of  connective  tissues  may  be  thus  classified: 

White  fibrous. 

Elastic. 

Areolar. 

Gelatinous. 


THE    WHITE     FIBROUS     TISSUE 


33 


Adenoid  or  retiform. 
Adipose. 
Neuroglia. 
Cartilage, 
i.  Hyaline. 

2.  White  fibrous. 

3.  Elastic. 
Bone  and  dentine. 

The  White  Fibrous  Tissue.  It  is  found  typically  in  tendon;  also 
in  ligaments,  in  the  periosteum  and  perichondrium,  the  dura  mater,  the  peri- 
cardium, the  sclerotic  coat  of  the  eye,  the  fibrous  sheath  of  the  testicle,  in  the 
fascia;  and  aponeuroses  of  muscles,  and  in  the  sheaths  of  lymphatic  glands. 

Structure.  To  the  naked  eye,  tendons  and  many  of  the  fibrous  membranes, 
when  in  a  fresh  state,  present  an  appearance  as  of  watered  silk.     This  is  due 


Fig.  38. 

Fig.  38. — Mature  White  Fibrous  Tissue  of  Tendon,  Consisting  Mainly  of  Fibers  with  a  Few- 
Scattered  Fusiform  Cells.      (.Strieker.) 

Fig.  39. — Caudal  Tendon  of  Young  Rat,  Showing  the  Arrangement,  Form,  and  Structure  of  the 
Tendon  Cells.      X  300.     (Klein.) 

to  the  arrangement  of  the  fibers  in  wavy  parallel  bundles.  Under  the  micro- 
scope the  tissue  appears  to  consist  of  long,  often  parallel,  bundles  of  fibers  of 
different  sizes.  The  cells  in  tendons,  figure  39,  are  arranged  in  long  chains  in 
the  ground  substance  separating  the  bundles  of  fibers,  and  are  more  or  less  regu- 
larly quadrilateral  with  large  round  nuclei  containing  nucleoli,  generally 
placed  so  as  to  be  contiguous  in  two  cells.  Each  of  these  cells  consists  of  a 
thick  body  from  which  processes  pass  in  various  directions  into,  and  partially 
fill  up  the  spaces  between,  the  bundles  of  fibers.  The  rows  of  cells  are  sep- 
arated from  one  another  by  lines  of  cement-substance. 

Yellow   Elastic   Tissue.     Yellow  elastic   tissue   is   found  chiefly   in 
the  ligamentum  nuchae  of  the  ox,  horse,  and  other  animals;   the  ligamenta 
subflava  of  man;   the  arteries,  constituting  the  fenestrated  coat  of  Henle; 
3 


34 


CELL    DIFFERENTIATION    AND    THE    ELEMENTARY    TISSUES 


the  veins  in  the  lungs  and  trachea;   the  stylohyoid,  thyro-hyoid,  and  crico- 
thyroid ligaments;    in  the  true  vocal  cords;    and  in  areolar  tissue. 

Structure.  Elastic  tissue  occurs  in  various  forms,  from  a  structureless, 
elastic  membrane  to  a  tissue  whose  chief  constituents  are  bundles  of  fibers 
crossing  each  other  at  different  angles;  when  seen  in  bundles  elastic  fibers  are 

yellowish  in  color,  but  individual  fibers  are  not 
so  distinctly  colored.  The  varieties  of  the  tissue 
may  be  classified  as  follows: 

a.  Fine  elastic  fibrils,  which  branch  and 
anastomose  to  form  a  network.  This  variety 
of  elastic  tissue  occurs  chiefly  in  the  skin  and 
mucous  membranes,  in  subcutaneous  and  sub- 
mucous tissue,  in  the  lungs  and  true  vocal 
cords. 

b.  Thick  fibers,  sometimes  cylindrical,  some- 
times flattened,  which  branch,  anastomose  and 
form  a  network:  these  are  seen  most  typically  in 
the  ligamenta  subflava  and  also  in  the  ligamen- 
tum  nuchae  of  such  animals  as  the  ox  and  horse, 
in  which  that  ligament  is  largely  developed, 
figure  40. 

A  certain  number  of  connective-tissue  cells 
are  found  in  the  ground  substance  between  the 
elastic   fibers   which   make   up    this    variety  of  connective  tissue,  page  33. 

Areolar  Tissue.  This  variety  of  fibrous  tissue  has  a  very  wide  dis- 
tribution and  constitutes  the  subcutaneous,  subserous,  and  submucous  tis- 
sue. It  is  found  in  the  mucous  membranes,  in  the  true  skin,  and  in  the  outer 
sheaths  of  the  blood-vessels.  It  forms  sheaths  for  muscles,  nerves,  glands, 
and  the  internal  organs,  and,  penetrating  into  their  interior,  supports  and  con- 
nects the  finest  parts. 

Structure.  To  the  naked  eye  it  appears,  when  stretched  out,  as  a  fleecy, 
white,  and  soft  meshwork  of  fine  fibrils,  with  here  and  there  wider  films  joining 
in  it,  the  whole  tissue  being  evidently  elastic.  The  openness  of  the  meshwork 
varies  with  the  locality  from  which  the  specimen  is  taken.  Under  the  micro- 
scope it  is  found  to  be  made  up  of  fine  white  fibers,  which  interlace  in  a  most 
irregular  manner,  together  with  a  variable  number  of  elastic  fibers.  On  the 
addition  of  acetic  acid,  the  white  fibers  swell  up,  and  become  gelatinous  in 
appearance;  but  as  the  elastic  fibers  resist  the  action  of  the  acid,  they  may  still 
be  seen  arranged  in  various  directions,  sometimes  appearing  to  pass  in  a  more 
or  less  circular  or  spiral  manner  round  a  small  gelatinous  mass  of  changed 
white  fiber.     The  cells  of  areolar  tissues  are  connective-tissue  corpuscles. 

Gelatinous  Tissue.  Gelatinous  connective  tissue  forms  the  chief 
part  of  the  bodies  of  such  marine  animals  as  the  jelly-fish.     It  is  found  in 


Fig.  40. — Elastic  Fibers  from 
the  Ligamenta  Subflava.  X  200. 
(Sharpey.) 


ADENOID    OR    LYMPHOID    TISSUE 


35 


many  parts  of  the  human  embryo.     It  may  be  best  seen  in  the  "  Whartonian 
jelly"  of  the  umbilical  cord  and  in  the  enamel  organs  of  developing  teeth. 


wr  H  to 


Fig.  41. 


Fig.  42. 


Fig.  41. — Mucous  Connective  Tissue  from  the  Umbilical  Cord,     a.  Cells;  b,  fibrils. 
Fig.  42. — Part  of  a  Section  of  a  Lymphatic  Gland,  from  which  the  Corpuscles  have  been  for 
the  most  part  Removed,  showing  the  Adenoid  Reticulum.      (Klein  and  Noble  Smith.) 

Structure.  It  consists  of  cells,  which  in  the  jelly  of  the  enamel  organ 
are  stellate,  embedded  in  a  soft  jelly-like  intercellular  substance  which  forms 
the  bulk  of  the  tissue. 

Adenoid  or  Lymphoid  Tissue.  Distribution.  This  variety  of  tissue 
makes  up  the  stroma  of  the  spleen  and  lymphatic  glands,  and  is  found  also 


Fig.  43. — Portion  of  Submucous  Tissue  of  Gravid  Uterus  of  Sow.     a,  Branched  cells,  more  or 
less  spindle-shaped;   b,  bundles  of  connective  tissue.      (Klein.) 


in  the  thymus,  in  the  tonsils,  and  in  the  follicular  glands  of  the  tongue;  in 
Peyer's  patches,  in  the  solitary  glands  of  the  intestines,  and  in  the  mucous 
membranes  generally. 

Structure.     Adenoid  or  retiform  tissue  consists  of  a  very  delicate  network  of 


3C> 


OEI/L     DIFFERENTIATION     AND    THE     ELEMENTARY     TISSUES 


minute  fibrils,  figure  46.  The  network  of  fibrils  is  concealed  by  being  covered 
with  flattened  connective-tissue  corpuscles,  which  may  be  readily  dissolved 
in  caustic  potash,  leaving  the  network  bare.  The  network  consists  of  white 
fibers,  the  interstices  of  which  are  filled  with  lymph-corpuscles.  The  cement- 
substance  of  adenoid  tissue  is  very  fluid. 

Neuroglia.  This  form  of  connective  tissue  found  in  the  nervous  system 
is  described  on  page  77. 

Development  of  Fibrous  Tissues.  In  the  embryo  the  place  of  the  fibrous 
tissues  is  at  first  occupied  by  a  mass  of  roundish  cells,  derived  chiefly  from 
the  mesoderm,  but  also  from  ectoderm  and  from  entoderm.  These  develop 
either  into  a  network  of  branched  cells  or  into  groups  of  fusiform  cells, 
figure  43. 

The  cells  are  embedded  in  a  semifluid  albuminous  substance  derived 
probably  from  the  cells  themselves.  Later  this  formed  material  is  converted 
into  fibrils  under  the  influence  of  the  cells.  The  process  gives  rise  to  fibers 
arranged  in  the  one  case  in  interlacing  networks,  areolar  /issue,  in  the  other 


Fig.  44. — Blood- Vessels  of  Adipose  Tissue.  A,  Minute  flattened  fat-lobule,  in  which  the  vessels 
only  are  represented,  a.  The  terminal  artery;  v,  the  primitive  vein;  b,  the  fat-vesicles  of  one 
border  of  the  lobule  separately  represented.  X  ioo.  d.  Plan  of  the  arrangement  of  the  capillaries. 
c,  on  the  exterior  of  the  vesicles;   more  highly  magnified.      (Todd  and  Bowman.) 


in  parallel  bundles,  white  -fibrous  tissue.  In  the  mature  forms  of  purely 
fibrous  tissue  not  only  the  remnants  of  the  cell-substance,  but  even  the  nuclei, 
may  disappear.  The  embryonic  tissue,  from  which  elastic  fibers  are  developed, 
is  composed  of  fusiform  cells,  and  a  structureless  intercellular  substance. 
The  fusiform  cells  dwindle  in  size  and  eventually  disappear  so  completely 
that  in  mature  elastic  tissue  hardly  a  trace  of  them  is  to  be  found:  mean- 
while the  elastic  fibers  steadily  increase  in  size. 


ADIPOSE    TISSUE 


37 


Adipose  Tissue.  In  almost  all  regions  of  the  human  body  a  larger 
or  smaller  quantity  of  adipose  or  fatty  tissue  is  present.  Adipose  tissue  is 
almost  alwavs  found  seated  in  areolar  tissue,  and  forms  in  its  meshes  little 
masses  of  unequal  size  and  irregular  shape,  to  which  the  term  lobules  is  com- 
monly applied. 

Structure.  Adipose  tissue  consists  essentially  of  cells  which  present 
dark,  sharply  defined  edges  when  viewed  with  transmitted  light;  each 
consisting  of  a  structureless  and  colorless  membrane  or  bag  formed  of  the 
remains  of  the  original  protoplasm  of  the  cell,  filled  with  fat.     A  nucleus 


Fig.  45. — A  Lobule  of  Developing 
Adipose  Tissue  from  an  Eight- Months' 
Fetus,  a,  Spherical  or,  from  pressure, 
polyhedral  cells  with  large  central 
nucleus,  surrounded  by  a  finely  reticr 
ulated  substance  staining  uniformly 
with  hematoxylin.  b,  Similar  cells 
with  spaces  from  which  the  fat  has 
been  removed  bv  oil  of  cloves,  c.  Sim- 
ilar cells  showing  how  the  nucleus 
with  enclosing  protoplasm  is  being 
pressed  toward  periphery,  d.  Nucleus 
of  endothelium  of  investing  capilla- 
ries.   (McCarthy.)     Drawn  by  Treves. 


Fig.  46.  —  Branched  Connective- 
Tissue  Corpuscles,  Developing  into 
Fat-Cells.      (Klein.) 


is  always  present  in  some  part  or  other  of  the  cell  protoplasm,  but  in  the 
ordinary  condition  of  the  loaded  cell  it  is  not  easily  or  always  visible.  This 
membrane  and  the  nucleus  can  generally  be  brought  into  view  by  extracting 
the  fat  with  ether  and  by  staining  the  tissue. 

The  ultimate  cells  are  held  together  by  capillary  blood-vessels,  figure  44; 
while  the  little  clusters  thus  formed  are  grouped  into  small  masses,  and 
held  so,  in  most  cases,  by  areolar  tissue.  The  oily  matter  contained  in  the 
cells  is  composed  chiefly  of  the  compounds  of  fatty  acids  with  glycerin,  olein, 
stearin,  and  palmitin. 

Development  of  Adipose  Tissue.  Fat  cells  are  developed  from  connective- 
tissue  corpuscles.  In  the  infra-orbital  connective  tissue  there  are  cells  ex- 
hibiting every  intermediate  gradation  between  an  ordinary  branched  connec- 
tive-tissue corpuscle  and  mature  fat  cells.     Their  developmental  appearance 


38  CELL     DIFFERENTIATION     AND     THE     ELEMENTARY     TISSUES 

is  as  follows:  a  few  small  drops  of  oil  make  their  appearance  in  the  proto- 
plasm, and  by  their  confluence  a  larger  drop  is  produced,  figure  45.  This 
gradually  increases  in  size  at  the  expense  of  the  original  protoplasm  of  the 
cell,  which  becomes  correspondingly  diminished  in  quantity  till  in  the  mature 
cell  it  forms  only  a  thin  crescentic  film  with  a  nucleus  closely  pressed  against 
the  cell-wall.     Under  certain  circumstances  this  process  may  be  reversed. 

A  large  number  of  blood-vessels  are  developed  in  adipose  tissue,  which 
subdivide  until  each  lobule  of  fat  contains  a  fine  meshwork  of  capillaries 
ensheathing  each  individual  fat-globule,  figure  44. 

Adipose  tissue  serves  as  a  storehouse  of  combustible  matter  which  may 
be  reabsorbed  into  the  blood  when  occasion  requires,  and,  being  used  up 
in  the  metabolism  of  the  tissues,  may  help  to  preserve  the  heat  of  the  body. 
That  part  of  the  fat  which  is  situated  beneath  the  skin  must,  by  its  want  of 
conducting  power,  assist  in  preventing  undue  waste  of  the  heat  of  the  body 
by  escape  from  the  surface. 

CARTILAGE. 

All  kinds  of  cartilage  are  composed  of  cells  embedded  in  a  substance 
called  the  matrix.  The  apparent  differences  of  structure  met  with  in  the 
various  kinds  of  cartilage  are  more  due  to  differences  in  the  character  of 
the  matrix  than  of  the  cells.     With  the  exception  of  the  articular  variety, 


Fig.  47. — Hyaline  Articular  Cartilage  (Human).     The  cell  bodies  entirely  fill    the    spaces   in 
the  matrix.      X  340  diams.    (Schafer.) 

cartilage  is  invested  by  a  thin  but  tough  firm  fibrous  membrane  called  the 
perichondrium. 

Cartilage  exists  in  three  different  forms  in  the  human  body,  viz.,  hyaline 
cartilage,  yellow  elastic  cartilage,  and  white  Jibro-cartilage. 

Hyaline  Cartilage.      This  variety  of  cartilage  is  met  with  largely  in 


HYALINE     CARTILAGE 


39 


the  human  body  where  it  invests  the  articular  ends  of  bones,  and  forms  the 
costal  cartilages,  the  nasal  cartilages,  and  those  of  the  larynx  with  the  ex- 


Fig.  48. — Fresh  Cartilage  from  the  Triton.     (A.  Rollett.) 

ception  of  the  epiglottis  and  cornicula  laryngis,  the  cartilages  of  the  trachea 
and  bronchi. 

Structure.  Like  other  cartilages  it  is  composed  of  cells  embedded  in  a 
matrix.  The  cells  are  irregular  in  shape,  generally  grouped  together  in 
patches,  figure  47.  The  patches  are  of  various  shapes  and  sizes  and  placed 
at  unequal  distances  apart.     They  generally  appear  flattened  near  the  free 


Fig.  49. — Costal  Cartilage  from  an  Adult  Dog.  showing  the  Fat-Globules  in  the  Cartilage  Cells. 

(Cadiat.) 

surface  of  the  mass  of  cartilage,  and  more  or  less  perpendicular  to  the  surface 
in  the  more  deeply  seated  portions. 

The  intercellular  substance  of  hyaline  cartilage,  when  viewed  fresh  or 
after  ordinary  fixation,  appears  homogeneous.  However,  when  subjected 
to  special  methods,  the  seemingly  homogeneous  intercellular  substance  can 


40 


CELL     DIFFERENTIATION    AND    THE     ELEMENTARY  TISSUES 


be  shown  to  be  made  up  of  fibers,  comparable  with  those  found  in  white 
fibrous  tissue,  embedded  in  the  homogeneous  matrix. 

In  the  hyaline  cartilage  of  the  ribs  the  cells  are  mostly  larger  than  in 
the  articular  variety  and  there  is  a  tendency  to  the  development  of  fibers 


Fig.  50. — Yellow  Elastic  Cartilage  of  the  Ear.     Highly  magnified.      (Hertwig.) 

in  the  matrix,  figure  49.     The  costal  cartilages  also  frequently  become  calcified 
in  old  age,  as  also  do  some  of  those  of  the  larynx. 

In  the  fetus  cartilage  is  the  material  of  which  the  bones  are  first  con- 
structed;   the  "model"  of  each  bone  being  laid  down,  so  to  speak,  in  this 

aiuiilMld  !    1  BfcliJii-'ifi 


■  •'■i,ffe>/. 


Fig.  51. — White  Fibro-Cartilage.     (Cadiat.) 


substance.  In  such  cases  the  cartilage  is  termed  temporary.  It  closely 
resembles  the  ordinary  hyaline  cartilage  but  the  cells  are  more  uniformly 
distributed  throughout  the  matrix. 


BONE 


41 


Elastic  and  White  Fibro-Cartilage.  The  first  variety  is  found  in 
the  cartilage  of  the  external  ear;  the  latter  in  portions  of  the  joints,  the  inter- 
vertebral cartilages,  etc. 

Structure.  Elastic  and  white  fibro-cartilage  are  composed  of  cells  and  a 
matrix;  the  latter  being  made  up  almost  entirely  of  fibers  closely  resembling 
those  of  fibrous  connective  tissue. 

Development  oj  Cartilage.  Cartilage  is  developed  out  of  mesoblast  cells 
with  a  very  small  quantity  of  intercellular  substance.  The  cells  multiply  by 
fission  within  the  cell-capsules. 

BONE. 


The  characteristic  of  bone  is  that  the  matrix  is  solidified  by  a  deposit  of 
earthy  salts,  chiefly  calcium  phosphate,  but  some  magnesium  phosphate  and 
calcium  carbonate. 

To  the  naked  eye  there  appear  two  plans  of  structure  in  different  bones, 
and  in  different  parts  of  the  same  bone,  namely,  the  dense  or  compact,  and 
the  spongy  or  cancellous  tissue.  In  a  longitudinal  section  of  a  long  bone, 
as  the  humerus,  the  articular  extremities  are  found  capped  on  their  surface 
by  a  thin  shell  of  compact  bone,  while  their  interior  is  made  up  of  the  spongy 
or  cancellous  tissue.  The  shaft  is  formed  almost  entirely  of  a  thick  layer 
of  the  compact  bone  which  -surrounds  a  central  canal,  the  medullary  cavity, 
so  called  from  its  containing  the  medulla,  or  marrow.  In  the  flat  bones,  the 
parietal  bone  or  the  scapula,  a  layer  of  cancellous  structure  lies  between 
two  layers  of  the  compact  tissue.  In  the  short  and  irregular  bones,  as  those 
of  the  carpus  and  tarsus,  the  cancellous  tissue  alone  fills  the  interior,  while 
a  thin  shell  of  compact  bone  forms  the  outside. 

The  Marrow.  There  are  two  distinct  varieties  of  marrow — the 
red  and  the  yellow. 


Fig.  52. — Cells  of  the  Red  Marrow  of  the  Guinea-Pig,  highly  magnified,  a,  A  large  cell,  the 
nucleus  of  which  appears  to  be  partly  divided  into  three  by  constrictions;  b,  a  cell,  the  nucleus  of 
which  shows  an  appearance  of  being  constricted  into  a  number  of  smaller  nuclei;  c,  a  so-called 
giant  cell,  or  .nyeloplaxe,  with  many  nuclei;  d,  a  smaller  myeloplaxe,  with  three  nuclei;  e-i,  proper 
cells  of  the  marrow.      (SchaferJ 


42 


CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


Red  marrow  is  that  variety  which  occupies  the  spaces  in  the  cancellous 
tissue;  it  is  highly  vascular,  and  thus  maintains  the  nutrition  of  the  spongy 
bone,  the  interstices  of  which  it  fills.  It  contains  a  few  fat  cells  and  a  large 
number  of  marrow  cells,  many  of  which  are  undistinguishable  from  lymphoid 
corpuscles,  and  has  for  a  basis  a  small  amount  of  fibrous  tissue.  Among 
the  cells  are  some  nucleated  cells  containing  hemoglobin  like  the  blood- 
corpuscles.  There  are  also  a  few  large  cells  with  many  nuclei,  termed  giant 
cells  or  myeloplaxes,  which  are  probably  derived  from  the  ordinary  marrow 
cells,  figure  52. 

Yellow  marrow  fills  the  medullary  cavity  of  long  bones,  and  consists 
chiefly  of  fat  cells  with  numerous  blood-vessels.  Many  of  its  cells  are  in 
every  respect  similar  to  lymphoid  corpuscles. 

From  these  marrow  cells,  especially  those  of  the  red  marrow,  the  red 
blood-corpuscles  are  derived. 

The  Periosteum  and  Nutrient  Blood-Vessels.  The  surfaces  of 
bones,   except  the  part  covered  with  articular  cartilage,   are  clothed  by  a 


Fig.  53. — Transverse  Section  of  Compact  Bone  (of  humerus').  Three  of  the  Haversian  canals 
are  seen,  with  their  concentric  rings;  also  the  lacuna:,  with  the  canaliculi  extending  from  them  across 
the  direction  of  the  lamella:.  The  Haversian  apertures  were  filled  with  debris  in  grinding  down 
the  section,  and  therefore  appear  black  in  the  figure,  which  represents  the  object  as  viewed  with 
transmitted  light.  The  Haversian  systems  are  so  closely  packed  in  this  section,  that  scarcely  any 
inteni'isal  lamella:  are  visible.      X   150.      (Sharpey.) 


tough,  fibrous  membrane,  the  periosteum,  which  is  closely  attached  to  the 
surface  of  the  bone.  Blood-vessels  are  distributed  in  this  membrane,  and 
minute  branches  from  these  periosteal  vessels  enter  the  Haversian  canals 


MICROSCOPIC     STRICTURE     OF     BONE 


43 


to  supply  blood  to  the  solid  part  of  the  bone.  The  long  bones  are  supplied 
also  by  a  proper  nutrient  artery  which,  entering  at  some  part  of  the  shaft 
so  as  to  reach  the  medullary  canal,  breaks  up  into  branches  for  the  supply 
of  the  marrow,  from  which  again  small  vessels  are  distributed  to  the  interior 
of  the  bone.  Other  small  nutrient  vessels  pierce  the  articular  extremities 
for  the  supply  of  the  cancellous  tissue. 

Microscopic  Structure  of  Bone.  Notwithstanding  the  differences 
of  arrangement  just  mentioned,  the  structure  of  all  compact  bone  substance 
is  found  under  the  microscope  to  be  essentially  the  same. 

Examined  with  a  rather  high  power  its  substance  is  found  to  contain  a 
multitude  of  small  irregular  spaces,  approximately  fusiform  in  shape,  called 
lacuna,  with  very  minute  canals  or  canaliculi,  as  they  are  termed,  leading 


1  Sil.it 


J IM  IP 


If  lip  lit 


Fig    54. — Longitudinal  Section  from  the  Human  Ulna,  Showing  Haversian  Canals,  Lacuna?,  and 

Canaliculi.      (Rollett.) 

from  them,  and  anastomosing  with  similar  prolongations  from  other  lacunae, 
figure  53.  In  very  thin  layers  of  bone,  no  other  canals  than  these  may  be  visi- 
ble; but  on  making  a  transverse  section  of  the  compact  tissue  of  a  long  bone, 
as  the  humerus  or  ulna,  the  arrangement  shown  in  figure  53  can  be  seen. 
The  bone  seems  mapped  out  into  small  circular  districts,  at  or  about  the 
center  of  each  of  which  is  a  hole,  around  which  are  concentric  layers,  the 
la  mcllaz,  the  lacuna  and  canaliculi  following  the  same  concentric  distribution 
around  the  center,  with  which  indeed  they  communicate. 

On  making  a  longitudinal  section,  the  central  holes  are  shown  to  be 
simply  the  cut  extremities  of  small  canals  which  run  lengthwise  through 
the  bone,  anastomosing  with  each  other  by  lateral   branches,  figure  54,  and 


44 


CELL     DIFFERENTIATION     AND    THE    ELEMENTARY     TISSUES 


are  called  Haversian  Canals,  after  the  name  of  the  physician,  Clopton 
Havers,  who  first  accurately  described  them. 

The  Haversian  Canals.  The  average  diameter  of  the  Haversian  canals 
is  50  jx.  They  contain  blood-vessels,  and  by  means  of  them  blood  is  con- 
veyed to  even  the  densest  parts  of  the  bone;  the  minute  canaliculi  and  lacunae 
absorbing  nutrient  matter  from  the  Haversian  blood-vessels  and  conveying 
it  still  more  intimately  to  the  very  substance  of  the  bone  which  they  traverse. 
The  blood-vessels  enter  the  Haversian  canals  both  from  without  from  the 
periosteum,  and  from  within  from  the  medullary  cavity  or  from  the  can- 
cellous tissue.     The  arteries  and  veins  usually  occupy  separate  canals. 

The  lacuna  are  occupied  by  branched  cells,  the  bone-cells  or  bone-corpus- 
cles, figure  55,  which  very  closely  resemble  the  ordinary  branched  connective- 
tissue  corpuscles.  The  processes  of  the  bone-cells  extend  into  the  canaliculi. 
Each  cell  controls  the  nutrition  of  the  bone  immediately  surrounding  it. 
Each  lacunar  corpuscle  communicates  with  the  others  in   its  surrounding 


Fig.  ss. — Bone-Corpuscles  with  their  Processes  as  Seen  in  a  thin  Section  of   Human   Bone. 

(Rollett.) 


district,  and  with  the  blood-vessels  of  the  Haversian  canals  by  means  of  the 
ramifications  just  described. 

It  will  be  seen  from  the  above  description  that  bone  bears  a  very  close 
structural  resemblance  to  what  may  be  termed  typical  connective  tissue. 
The  bone  corpuscles  with  their  processes  occupying  the  lacunas  and  canalic- 
uli correspond  exactly  to  the  cornea-corpuscles  lying  in  the  branched  spaces. 

The  Lamella.  0}  Compact  Bone.  In  the  shaft  of  a  long  bone  three  distinct 
sets  of  lamellae  can  be  clearly  recognized:  General  or  fundamental  lamellae, 
which  are  just  beneath  the  periosteum  and  parallel  with  it,  and  around  the 
medullary  cavity;  Special  or  Haversian  lamellae,  which  are  concentrically 
arranged  around  the  Haversian  canals  to  the  number  of  six  to  eighteen  around 
each;  Interstitial  lamellae,  which  connect  the  systems  of  Haversian  lamellae, 


DEVELOPMENT    OF     BONE 


45 


filling  the  spaces  between  them,  and  consequently  attaining  their  greatest 
development  where  the  Haversian  systems  are  few. 

The  ultimate  structure  of  the  lamellae  appears  to  be  fibrous.  A  thin 
film  peeled  off  the  surface  of  a  bone,  from  which  the  earthy  matter  has  been 
removed  by  acid,  is  composed  of  a  finely  reticular  structure,  formed  apparently 
of  very  slender  fibers  decussating  obliquely,  but  coalescing  at  the  points  of 
intersection,  as  if  here  the  fibers  were  fused  rather  than  woven  together. 


Fig.  56. — Lamelloe  Torn  Off  from  a  Decalcified  Human  Parietal  Bone  at  some  Depth  from  the 
Surface,  a,  a,  Lamelke,  showing  reticular  fibers;  b,  b,  darker  part,  where  several  lamellae  are 
superposed;  c,  perforating  fibers.  Apertures  through  which  perforating  fibers  had  passed,  are 
seen  especially  in  the  lower  part,  a,  a,  ot  the  figure.      (Allen  Thomson.) 


The  reticular  lamellae  are  perforated  by  the  perforating  fibers  of  Sharpey, 
which  bolt  the  neighboring  lamella?  together,  and  may  be  drawn  out  when 
the  latter  are  torn  asunder,  figure  56.  These  perforating  fibers  originate  from 
ingrowing  processes  of  the  periosteum,  and  in  the  adult  still  retain  their 
connection  with  it. 

Development  of  Bone.  From  the  point  of  view  of  their  develop- 
ment, all  bones  may  be  subdivided  into  two  classes: 

Those  which  are  ossified  directly  in  membrane  or  fibrous  tissue,  e.g.,  the 
bones  forming  the  vault  of  the  skull,  parietal,  frontal,  and  a  certain  portion 
of  the  occipital  bones; 

Those  whose  form,  previous  to  ossification,  is  laid  in  down  hyaline  carti- 
lage, e.g.,  humerus,  femur,  etc. 

The  process  of  development,  pure  and  simple,  may  be  best  studied  in 
bones  which  are  not  preceded  by  cartilage,  i.e.,  membrane-formed.  Without 
a  knowledge  of  ossification  in  membrane  it  is  difficult  to  understand  the  much 
more  complex  series  of  changes  through  which  such  a  structure  as  the  carti- 


4(>  CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 

laginous  femur  of  the  fetus  passes  in  its  transformation  into  the  bony  femur 
of  the  adult  (ossification  in  cartilage). 

Ossification  in  Membrane.  The  membrane,  afterward  forming  the 
periosteum,  from  which  such  a  bone  as  the  parietal  is  developed,  consists 
of  two  layers,  an  external  fibrous,  and  an  internal  cellular  or  osteogenetic. 

The  external  layer  consists  of  ordinary  connective  tissue,  with  branched 
corpuscles  here  and  there  between  the  bundles  of  fibers.  The  internal  layer 
consists  of  a  network  of  fine  fibrils  with  nucleated  cells  and  ground  or  cement 
substance  between  the  fibrous  bundles.  It  is  more  richly  supplied  with 
capillaries  than  the  outer  layer.  The  relatively  large  number  of  its  cellular 
elements,  together  with  the  abundance  of  blood-vessels,  clearly  mark  it  as 
the  portion  of  the  periosteum  which  is  immediately  concerned  in  the  for- 
mation of  bone. 

In  such  a  bone  as  the  parietal  there  is  first  an  increase  in  vascularity, 
followed  by  the  deposition  of  bony  matter  in  radiating  spicula,  starting 
from  a  center  oj  ossification.  These  primary  bony  spicula  are  osteogenetic 
fibers,  composed  of  osteogen,  in  which  calcareous  granules  are  deposited. 
Calcareous  granules  are  deposited  also  in  the  interfibrillar  matrix.  By 
the  junction  of  the  osteogenetic  fibers  and  their  resulting  bony  spicula  a 
meshwork  of  bone  is  formed.  The  osteoblasts,  being  in  part  retained  within 
the  bone  trabecular  thus  produced,  form  bone-corpuscles.  Lime  salts  are 
deposited  in  the  circumferential  part  of  each  osteoblast,  and  thus  a  ring 
of  osteoblasts  gives  rise  to  a  ring  of  bone  with  the  remaining  uncalcified 
portions  of  the  osteoblasts  embedded  in  it  as  bone-corpuscles.  At  the  same 
time  the  plate  increases  at  the  periphery  by  the  extension  of  the  bony  spicula 
and  by  deposits  taking  place  from  the  osteogenetic  layer  of  the  periosteum. 
The  bulk  of  the  primitive  spongy  bone  is  gradually  converted  into  compact 
bony  tissue  of  the  Haversian  systems. 

Ossification  in  Cartilage.  Under  this  heading,  taking  the  femur 
as  a  typical  example,  we  may  consider  the  process  by  which  the  solid  cartilag- 
inous rod  which  represents  the  bone  in  the  fetus  is  converted  into  the  hollow 
cylinder  of  compact  bone  with  expanded  ends  formed  of  cancellous  tissue 
in  the  adult  long  bone. 

The  fetal  cartilage  is  sheathed  in  a  membrane  termed  the  perichondrium, 
which  resembles  the  periosteum  described  above.  Thus,  the  differences 
between  the  fetal  perichondrium  and  the  periosteum  of  the  adult  are  such 
as  usually  exist  between  the  embryonic  and  mature  forms  of  connective  tissue. 

There  are  several  steps  in  the  transformation  of  the  fetal  cartilage  to  the 
adult  bone,  due  to  the  fact  that  there  is  first  an  impregnation  of  the  cartilage 
with  lime  salts,  followed  later  by  the  resorption  of  this  entire  material  with 
formation  of  the  embryonic  spongy  bone,  which  is  later  replaced  by  the  per- 
manent bone.  The  complicated  phenomenon  takes  place  in  steps  or  stages  as 
follows: 


OSSIFICATION     IN     CARTILAGE 


47 


Stage  oj  Proliferation  and  Calcification.  The  cartilage  cells  in  and  near 
the  center  of  ossification  become  enlarged,  proliferate,  and  arrange  them- 
selves in  rows  in  the  long  axis  of  the  fetal  cartilage,  figure  57.  Lime  salts  are 
next  deposited  in  fine  granules  in  the  hyaline  matrix  of  the  cartilage,  and  this 
gradually  becomes  transformed  into  calcified  trabecular,  figure  57.  The  en- 
larging cartilage  cells  become  more  transparent,  and  finally  disintegrate, 
the  spaces  occupied  by  them  forming  the  primordial  marrow  cavities.     During 


'^,  '^r  '«^'< 
"S-:  Ss»3  £^v| 


sHr 


Us 


Fig.  57. — Developing  Bone  o!  Femur  of  the  Rabbit.  (Schafer,  from  Klein.)  X  350.  a, 
Cartilage  cells;  b,  cartilage  cells  enlarged  in  the  region  of  calcifying  matrix;  c,  d,  trabecuteof  cal- 
cifying cartilage  covered  with  c ,  osteoblasts;  /,  osteoclasts  eroding  the  trabecular  g,  h,  disappear- 
ing cartilage  cells.  The  osteoblasts- are  seen  to  be  depositing  layers  of  bony  substance.  Loops 
of  blood-vessels  extend  to  the  limit  of  the  region  in  which  the  bone  is  forming. 


this  stage  the  perichondrium  has  become  the  periosteum,  and  is  beginning 
to  deposit  bone  on  the  outside  of  the  cartilage. 

Stage  oj  Vascularization  0}  the  Cartilage.  Processes  from  the  osteo- 
genetic  layer  of  the  periosteum  containing  blood-vessels  break  through  the 
bone  into  the  primordial   marrow  cavities  and  form  the  primary  marrow, 


48 


CELL     DIFFERENTIATION     AND    THE    ELEMENTARY     TISSUES 


beginning  at  the  centers  of  ossification,  and  spreading  chiefly  up  and  down 
the  shaft. 

Stage  of  Substitution  0}  Embryonic  Spongy  Bone  for  Calcified  Cartilage. 
The  cells  of  the  primary  marrow  arrange  themselves  as  a  continuous  epi- 
thelium-like layer  on  the  calcified  trabecular  and  deposit  a  layer  of  bone, 


Fig.  58. — Transverse  Section  through  the  Tibia  of  a  Fetal  Kitten,  semidiagrammatic.  X  60. 
P,  Periosteum.  O,  Osteogenetic  layer  of  the  periosteum,  showing  the  osteoblasts  arranged  side  by 
side,  represented  as  pear-shaped  black  dots  on  the  surface  of  the  newly  formed  bone.  B,  The  peri- 
osteal bone  deposited  in  successive  layers  beneath  the  periosteum  and  ensheathing  E,  the  spongy 
endochondral  bone;  represented  as  more  deeply  shaded.  Within  the  trabecular  of  endochondral 
spongy  bone  are  seen  the  remains  of  the  calcified  cartilage  trabecular  represented  as  dark  wavy 
lines.  C,  The  medulla,  with  V,  V,  veins.  In  the  lower  half  of  the  figure  the  endochondral  spongy 
bone  has  been  completely  absorbed.      (Klein  and  Noble  Smith.) 


and  ensheath  them.     The  encased  trabecular    are  gradually  absorbed    by 
the  osteoclasts  of  Kolliker. 

These  stages  are  precisely  similar  to  what  goes  on  in  the  growing  shaft 
of  a  bone  which  is  increasing  in  length  by  the  advance  of  the  process  of  ossifi- 
cation into  the  intermediary  cartilage  between  the  diaphysis  and  epiphysis. 
In  this  case  the  cartilage  cells  become  flattened  and,  multiplying  by  division, 


OSSIFICATION    IN    CARTILAGE 


49 


are  grouped  into  regular  columns  at  right  angles  to  the  plane  of  calcifi- 
cation while  the  process  of  calcification  extends  into  the  hyaline  matrix 
between  them, 

The  embryonic  spongy  bone,  formed  as  above  described,  is  simply  a  tem- 
porary tissue  occupying  the  place  of  the  fetal  rod  of  cartilage;  the  preceding 
stages  show  the  successive  changes  at  the  center  of  the  shaft.  Periosteal 
bone  is  at  the  same  time  deposited  in  successive  layers  beneath  the  perios- 
teum at  the  circumference  of  the  shaft,  exactly  as  described  in  the  section 
on  ossification  in  membrane,  and  thus  a  casing  of  periosteal  bone  is  formed 
around  the  embryonic  endochondral  spongy  bone.     The  embryonic  spongy 


Fig.  59. — Transverse  Section  of  Femur  of  a  Human  Embryo  about  Eleven  "Weeks  Old.  a. 
Rudimentary  Haversian  canal  in  cross-section;  b,  in  longitudinal  section;  c,  osteoblasts;  d,  newly 
formed  osseous  substance  of  a  lighter  color;  e,  that  of  greater  age;  f,  lacunar  with  their  cells;  g, 
a  cell  still  united  to  an  osteoblast.     (Frey.) 


bone  is  absorbed,  through  the  agency  of  the  osteoclasts,  until  the  trabecular 
are  replaced  by  one  great  cavity,  the  medullary  cavity  of  the  shaft. 

Stage  of  Formation  of  Compact  Bone.  The  transformation  of  spongy 
periosteal  bone  into  compact  bone  is  effected  in  a  manner  exactly  similar 
to  that  which  has  been  described  in  connection  with  ossification  in  mem- 
brane, page  46.  The  irregularities  in  the  walls  of  the  spongy  periosteal 
bone  are  absorbed  by  the  osteoclasts,  while  the  osteoblasts  which  line 
them  are  developed  in  concentric  layers,  each  layer  in  turn  becoming  ossified 
till  the  comparatively  large  space  in  the  center  is  reduced  to  a  well-formed 
Haversian  canal,  figure  59.     When  once  formed,  bony  tissue  grows  to  some 


50 


CELL    DIFFERENTIATION    AND    THE     ELEMENTARY    TISSUES 


extent  inter stitially,  as  is  evidenced  by  the  fact  that  the  lacunae  are  rather 
further  apart  in  full-formed  than  in  young  bone. 

It  will  be  seen  that  the  common  terms  ossification  in  cartilage  and  ossifi- 
cation in  membrane  are  apt  to  mislead,  since  they  seem  to  imply  two  processes 
radically  distinct.  The  process  of  ossification,  however,  is  in  all  cases  one 
and  the  same,  all  true  bony  tissue  being  formed  from  membrane,  perichon- 
drium or  periosteum;  but  in  the  development  of  such  a  bone  as  the  femur, 
lime  salts  are  first  of  all  deposited  in  the  cartilage;  this  calcified  cartilage, 
however,  is  gradually  and  entirely  reabsorbed,  replaced  by  bone  formed 
from  the  periosteum.  Thus  calcification  of  the  cartilaginous  matrix  pre- 
cedes the  real  formation  of  bone.  We  must,  therefore,  clearly  distinguish 
between  calcification  and  ossification.  The  former  is  simply  the  infiltration 
of  an  animal  tissue  with  lime  salts,  while  ossification  is  the  formation  of 
true  bone. 

Growth  of  Bone.  Bones  increase  in  length  by  the  advance  of  the 
process  of  ossification  into  the  cartilage  intermediate  between  the  diaphysis 
and  epiphysis.  The  increase  in  length  indeed  is  due  entirely  to  growth 
at  the  two  ends  of  the  shaft.  Increase  in  thickness  in  the  shaft  of  a  long 
bone  occurs  by  the  deposition  of  successive  layers  beneath  the  periosteum. 
If  a  thin  metal  plate  be  inserted  beneath  the  periosteum  of  a  growing  bone 
it  will  soon  be  covered  by  osseous  deposit,  but  if  it  be  put  between  the  fibrous 
and  osteogenetic  layers  it  will  never  become  enveloped  in  bone,  for  all  the 
bone  is  formed  beneath  the  latter. 


THE  TEETH. 

During  the  course  of  his  life,  man,  in  common  with  most  other  mammals, 
is  provided  with  two  sets  of  teeth;  the  first  set,  called  the  temporary  or  milk- 
teeth  of  infancy,  are  shed  and  replaced  by  the  second  or  permanent  set. 


Molars. 


Canine. 


Temporary   Teeth. 

Middle   Line    of   Jaw. 


Incisors. 


Incisors. 


Canine. 


Molars. 

2         =  IO 


2         =  IO 


The  figures  indicate  in  months  the  age  at  which  each  tooth  appears 

LOWER  CENTRAL 
INCISORS. 

UPPER 
INCISORS. 

FIRST  MOLAR   AND 

LOWER  LATERAL 

INCISORS. 

CANINES. 

SECOND 

MOLARS. 

6  to  9 

8  to  12 

12  tO   15 

18  to  24 

24  to  30 

THE    TEETH 


51 


Permanent   Teeth. 

Middle    Line    of  Jaw. 


jfiars.       SPoidaSrs°r      Canine.     Incisors. 


T • „       n ■   „        Bicuspids  or        True 

Incisors.     Canine.         Prei£olars.       Molars. 


The  age  at  which  each  permantnt  tooth  is  cut  is  indicated  in  this  table  in  years: 


FIRST 

INCISORS. 

BICUSPIDS  OR  PRE- 
MOLARS. 

CANINES. 

SECOND 
MOLARS. 

THIRD 

MOLARS. 

Centrals. 

Laterals. 

First. 

Second. 

WISDOMS. 

6 

7 

8 

9 

IO 

12  tO   14 

12  tO   15 

17  to  25 

Structure.  A  tooth  is  generally  described  as  possessing  a  crown, 
neck,  and  root  or  roots.  The  crown  is  the  portion  which  projects  beyond 
the  level  of  the  gum.  The  neck  is  that  constricted  portion  just  below  the  crown 
which  is  embraced  by  the  free  edges  of  the  gum,  and  the  root  includes  all 
below  this. 

On  making  longitudinal  and  transverse  sections  through  its  center,  figure 
61,  A,  B,  a  tooth  is  found  to  be  principally  composed  of  a  hard  superficial 


Fig.  60. — Normal  Well-formed  Jaws,  from  which  the  Alveolar  Plate  has  been  in  great  part 
Removed,  so  as  to  expose  the  Developing  Permanent  Teeth  in  their  Crypts  in  the  Jaws.     (Tomes.) 


material,  dentine  or  ivory,  which  is  hollowed  out  into  a  central  cavity  which 
resembles  in  general  shape  the  outline  of  the  tooth,  and  is  called  the  pulp- 
cavity. 

The  tooth  pulp  is  composed  of  fibrous  connective  tissue,  blood-vessels, 
nerves,  and  large  numbers  of  cells  of  varying  shapes,  and  on  the  surface  in 


52 


CELL     DIFFERENTIATION    AND     THE     ELEMENTARY    TISSUES 


close  connection  with  the  dentine  a  specialized  layer  of  cells  called  odonto- 
blasts, which  are  elongated  columnar  cells  with  a  large  nucleus  at  the  taper- 
ing ends  farthest  from  the  dentine.  The  cells  are  all  embedded  in  a  mucoid 
gelatinous  matrix. 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  opening 
at  the  apical  extremity  of  each  root. 

A  layer  of  very  hard  calcareous  matter,  the  enamel,  caps  the  dentine  of 
the  crown;  beneath  the  level  of  the  gum  is  a  layer  of  true  bone,  called  the 
cement  or  crusta  petrosa.  The  enamel  and  cement  are  very  thin  at  the  neck 
of  the  tooth  where  they  come  in  contact,  the  cement  overlapping  the  enamel. 
The  enamel  becomes  thicker  toward  the  crown,  and  the  cement  toward 
the  lower  end  or  apex  of  the  root. 

Dentine  or  Ivory. — Dentine  closely  resembles  bone  in  chemical  com- 
position.    It  contains,  however,  rather  less  animal  matter. 

Structure.  Dentine  is  finely  channelled  by  a  multitude  of  delicate  tubes, 
which  by  their  inner  ends  communicate  with  the  pulp-cavity,  and  by  their 


Fig.  6i. — A. — A  Longitudinal  Section  of   a  Human   Molar  Tooth,   c,  Cement;  d,  dentine;  e, 
enamel;    v,  pulp  cavity  (Owen).     B. —  Transverse  section.     The  letters  indicate  the  same  as  in  A. 


outer  extremities  come  into  contact  with  the  under  part  of  the  enamel  and 
cement,  and  sometimes  even  penetrate  them  for  a  greater  or  less  distance, 
figures  63,  64.  The  matrix  in  which  these  tubes  lie  is  composed  of  "  a  reti- 
culum of  fine  fibers  of  connective  tissue  modified  by  calcification,  and,  where 
that  process  is  complete,  entirely  hidden  by  the  densely  deposited  lime  salts" 
(Mummery). 

The  tubules  of  the  dentine  contain  fine  prolongations  from  the  tooth- 
pulp,  which  give  the  dentine  a  certain  faint  sensitiveness  under  ordinary 
circumstances  and,  without  doubt,  have  to  do  also  with  its  nutrition.  They 
are  probably  processes  of  the  dentine-cells  or  odontoblasts  lining  the  pulp- 
cavity.     The  relation  of    these  processes  to  the  tubules  in  which  they  lie  is 


ENAMEL 


53 


precisely  similar  to  that  of  the  processes  of  the  bone-corpuscles  to  the  canalic- 
uli  of  bone.  The  outer  portion  of  the  dentine,  underlying  the  cement  and 
the  enamel,  figure  63,  b,  c,  contains  cells  like  bone-corpuscles. 


Dentine  — 


Periosteum  of 

alveolus 


Cement 


Enamel 


Cement 


wj Lower  jaw  bone 


Fig.  62. — Premolar  Tooth  and  Surrounding  Bone  of  Cat. 

Enamel.  The  enamel,  which  is  by  far  the  hardest  portion  of  a 
tooth,  is  composed  chemically  of  the  same  elements  that  enter  into  the 
composition  of  dentine  and  bone,  but  the  animal  matter  amounts  only  to 


Fig.  63. — Section  of  a  Portion  of  the  Dentine  and  Cement  from  the  Middle  of  the  Root  of  an 
Incisor  Tooth,  a.  Dental  tubuli  ramifying  and  terminating,  some  of  them  in  the  interglobular 
spaces  b  and  c,  which  somewhat  resemble  bone  lacunae;  d,  inner  layer  of  the  cement  wjth  numerous 
closely  set  canaliculi;   e,  outer  layer  of  cement;   /.lacuna?;   g,  canaliculi.      X  35°-      (Kolliker.) 

about  2  or  3  per  cent.     It  contains  a  larger  proportion  of  inorganic  matter 
and  is  harder  than  any  other  tissue  in  the  body. 


54 


CELL    DIFFERENTIATION     AND     THE    ELEMENTARY    TISSUES 


Structure.  Enamel  is  composed  of  fine  hexagonal  fibers,  figures  64,  65. 
These  are  set  on  end  vertical  to  the  surface  of  the  dentine,  and  fit  into  cor- 
responding depressions  in  the  same. 

Like  the  dentine  tubules,  they  arc  disposed  in  wavy  and  parallel  curves. 
The  fibers  are  thus  marked  by  transverse  lines.  They  are  mostly  solid, 
but  some  of  them  may  contain  a  very  minute  canal. 


tr\  1} 


Fig.  64. 


Fig.  6s. 


Fig.  64. — Thin  Section  of  the  Enamel  and  a  Part  of  the  Dentine,  a,  Cuticular  pellicle  of  the 
enamel  (Nasmyth's  membrane);  b,  enamel  fibers,  or  columns  with  fissures  between  them  and  cross 
striae;  c,  larger  cavities  in  the  enamel,  communicating  with  the  extremities  of  some  of  the  dentinal 
tubuli  (d).      X  350.      (Kolliker.) 

Fig.  65. — Section  of  the  Upper  Jaw  of  a  Fetal  Sheep.  A. —  i.  Common  enamel  germ  dipping 
down  into  the  mucous  membrane;  2,  palatine  process  of  jaw;  3,  rete  Malpighi.  (Waldeyer.)  B. — 
Section  similar  to  A,  but  passing  through  one  of  the  special  enamel  germs  here  becoming  flask- 
shaped;  c,  c', epithelium  of  mouth;  f,  neck;  f,  body  of  special  enamel  germ.  (Rose.)  C. — A  later 
stage;  c,  outline  of  epithelium  of  gum;  f,  neck  of  enamel  germ;  /',  enamel  organ;  p,  papilla;  5, 
dental  sac  forming;  fp,  the  enamel  germ  of  permanent  tooth;  m,  bone  of  jaw;  v,  vessels  cut  across. 
(Kolliker.)     Copied  from  Quain's  "Anatomy." 


The  enamel  prisms  are  connected  together  by  a  trace  of  hyaline  cement- 
substance. 

Development.  The  first  step  in  the  development  of  the  teeth  consists 
in  a  downward  growth,  figure  65,  A,  i,  from  the  deeper  layer  of  stratified 


ENAMEL 


55 


epithelium  of  the  mouth,  which  first  becomes  thickened  in  the  neighborhood 
of  the  maxillae  or  jaws,  now  also  in  the  course  of  formation.  This  epidermal 
papilla  grows  downward  into  a  recess  of  the  imperfectly  developed  tissue  of  the 
embryonic  jaw.  It  forms  the  primary  enamel  organ  or  enamel  germ,  and 
its  position  is  indicated  by  a  slight  groove  in  the  mucous  membrane  of  the 
jaw.  The  next  step  consists  in  the  elongation  and  the  inclination  outward 
of  the  deeper  part,  figure  65,  b,  /',  of  the  enamel  germ,  followed  by  an 
increased  development  at  certain  points  corresponding  to  the  situations  of 
the  future  milk-teeth.  The  enamel  germ  becomes  divided  at  its  deeper 
portion,  or  extended  by  further  growth,  into  a  number  of  special  enamel 
germs  corresponding  to  each  of  the  milk-teeth,  and  connected  to  the  com- 
mon germ  by  a  narrow  neck.  Each  tooth  is  thus  placed  in  its  own  special 
recess  in  the  embryonic  jaw,  figure  65,  c,  /'. 

As  these  changes  proceed,  there  grows  up  from  the  underlying  tissue 
into  each  enamel  germ,  figure  65,  c,  p,  a  distinct  vascular  papilla,  dental 


Fig.  66. — Part  of  Section  cf  Developing  Tooth  of  a  Young  Rat,  showing  the  Mode  of  Deposi- 
tion of  the  Dentine.  Highly  magnified,  a.  Outer  layer  of  fully  formed  dentine;  b,  uncalcified 
matrix  with  one  or  two  nodules  of  calcareous  matter  near  the  calcified  parts;  c,  odontoblasts  send- 
ing processes  into  the  dentine;  d,  pulp;  e,  fusiform  or  wedge-shape  cells  found  between  odonto- 
blasts; /,  stellate  cells  of  pulp  in  fibrous  connective  tissue.  The  section  is  stained  in  carmine,  which 
colors  the  uncalcified  matrix  but  not  the  calcified  part.      (E.  A.  Schafer.) 


papilla,  and  upon  it  the  enamel  germ  becomes  molded,  and  presents  the 
appearance  of  a  cap  of  two  layers  of  epithelium  separated  by  an  interval, 
figure  65,  c,  /'.  While  part  of  the  sub-epithelial  tissue  is  elevated  to  form 
the  dental  papillae,  the  part  which  bounds  the  embryonic  teeth  forms  the 
dental  sacs,  figure  65,  C,  s  ;  and  the  rudiment  of  the  jaw  sends  up  processes 
forming  partitions  between  the  teeth.  The  papilla,  which  is  really  part 
of  the  dental  sac,  is  composed  of  nucleated  cells  arranged  in  a  meshwork, 
in  the  outer  layer  of  which  are  the  columnar  cells  called  odontoblasts.  The 
odontoblasts  form  the  dentine,  while  the  remainder  of  the  papilla  forms  the 
pulp.  The  method  of  the  formation  of  the  dentine  from  the  odontoblasts 
is  said  to  be  as  follows:  The  cells  form  elongated  orocesses  at  their  outer 
surfaces  which  are  directly  converted  into  the  tubules  of  dentine,  figure  66,  c, 
and  into  the  contained  fibrils. 


56 


CELL     DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


Each  papilla  early  takes  the  shape  of  the  crown  of  the  tooth  to  which 
it  corresponds,  but  as  the  dentine  increases  in  thickness  the  papilla  diminishes 
until  when  the  tooth  is  cut  only  a  small  amount  remains  as  the  pulp.  It  is 
supplied  by  vessels  and  nerves  which  enter  at  the  end  of  the  root.  The  roots 
are  not  completely  formed  at  the  time  of  the  eruption  of  the  teeth. 


Fig.  67. — Vertical  Transverse  Section  of  the  Dental  Sac,  Pulp,  etc.,  of  a  Kitten,  a.  Dental 
papilla  or  pulp;  b,  the  cap  of  dentine  formed  upon  the  summit;  c,  its  covering  of  enamel;  d,  inner 
layer  of  epithelium  of  the  enamel  organ;  e,  gelatinous  tissue;  f,  outer  epithelial  layer  of  the  enamel 
organ;   g,  inner  layer,  and  h,  outer  layer  of  dental  sac.      X   14.      (Thiersch.) 

The  enamel  cap  is  formed  by  the  enamel  cells,  by  the  deposit  of  a  keratin- 
like substance,  which  subsequently  undergoes  calcification.  Other  layers 
are  formed  in  the  same  manner  meanwhile. 

The  temporary  or  milk-teeth  are  speedily  replaced  by  the  growth  of  the 
permanent  teeth. 

The  development  of  tne  temporary  teeth  commences  about  the  sixth 
week  of  intra-uterine  life,  after  the  laying  down  of  the  bony  structure  of 
the  jaws.  Their  permanent  successors  begin  to  form  about  the  sixteenth 
week  of  intra-uterine  life. 


III.  MUSCULAR    TISSUE. 


There  are  two  chief  kinds  of  muscular  tissue,  differing  both  in  minute 
structure  as  well  as  in  mode  of  action,  viz.,  (i)  the  smooth  or  non-striated,  and 
(2)  the  striated. 


SMOOTH     OR    NON-STRIATED     MUSCLE 


57 


SMOOTH    OR    NON-STRIATED    MUSCLE. 

Non-striated  muscle  forms  the  proper  muscular  coats  of  the  digestive 
canal  from  the  middle  of  the  esophagus  to  the  internal  sphincter  ani;  of 
the  ureters  and  urinary  bladder;  of  the  trachea  and  bronchi;  of  the  ducts 
of  glands;  of  the  gall-bladder;  of  the  vesicular  seminales;  of  the  uterus  and 
Fallopian  tubes;  of  the  blood-vessels  and  lymphatics;  and  of  the  iris  and 
some  other  parts  of  the  eye.     This  form  of  tissue  also  enters  largely  into  the 


Fig.   68. — Isolated  Smooth  Muscle  Cells  from   Human  Small  Intestine.        X    400.      Rod-shaped 
nucleus  surrounded  by  area  of  finely  granular  protoplasm;  longitudinal  striations    of  cytoplasm. 

composition  of  the  tunica  dartos  of  the  scrotum.  Unstriped  muscular  tissue 
occurs  largely  also  in  the  true  skin  generally,  being  especially  abundant  in  the 
interspaces  between  the  bases  of  the  papillae,  and,  when  it  contracts,  the 
papillae  are  made  unusually  prominent,  giving  rise  to  the  peculiar  roughness 
of  the  skin  termed  cutis  anserina,  or  goose  flesh.     It  also  occurs  in  all  parts 


Fig.  69. — Smooth  Muscle  from  Intestine  of  Pig,  Showing  Syncytial  Structure.  a,  Pro- 
toplasmic process  connecting  two  muscle  fibers;  b,  end-to-end  union  of  two  muscle  fibers,  showing 
the  continuity  of  protoplasm  and  myofibrils;  c,  nucleus  of  muscle  fiber;  d,  granular  protoplasm  at 
the  end  of  muscle  nucleus;  e,  coarse  myofibril,  /,  Fine  myofibril;  g,  connective-tissue  cell  with 
connective-tissue  fibrils  surrounding  it;   h.  elastic  fiber.      (New  figure  by  Caroline  McGill.) 


where  hairs  occur,  in  the  form  of   flattened   roundish    bundles   which   lie 
alongside  the  hair-follicles  and  sebaceous  glands. 

Structure.  Unstriated  muscle  fibers  are  elongated,  spindle-shaped, 
mononucleated  cells,  7  to  8  ytx  in  diameter  by  40  to  200  fji  in  length,  figures 
68  and  69.  The  protoplasm  of  each  cell,  the  contractile  substance,  is 
marked  by  longitudinal  striations  representing  fibrils  which  have  been 
described  as  contractile.     The  nucleus  is  an  oblong  mass  placed  near  the 


58 


CELL    DIFFERENTIATION     AND     THE     ELEMENTARY     TISSUES 


center  of  the  cell.     It  is  covered  by  a  nuclear  membrane  which  encloses  a 
network  of  anastomosing  fibrils. 

Development.  In  the  pig  the  smooth  muscle  of  the  alimentary 
canal  originates  in  the  syncytium  of  the  mesodermal  cells  which  surround 
the  entoderm.  The  cells  soon  begin  to  grow  into  the  adult  spindle-shape 
form  and  the  fibrils  make  their  appearance.  Even  in  the  adult  muscle  the 
syncytial  connections  are  retained  according  to  Miss  McGill. 

Striated  Muscle. 

Striated  or  striped  muscle  constitutes  the  whole  of  the  muscular  apparatus 
of   the  skeleton,  of  the  walls  of   the  abdomen,  the  limbs,  etc. — the  whole 


Fig.  70. — Transverse  Section  through  Muscular  Fibers  of  Human  Tongue.  The  deeply  stained 
nuclei  are  situated  at  the  inside  of  the  sarcolemma.  Each  muscle  fiber  shows  "Cohnheim's  fields." 
that  is,  the  sarcous elements  in  transverse  section  separated  by  clear  (apparently  linear)  interstitial 
substance.      X  450.      (Klein  and  Noble  Smith.) 


Fig.  71. 


Fig.  72. 


Fig.  71. — Muscle  Fiber  Torn  Across;  the  sarcolemma  still  connects  the  two  parts  of  the  fiber. 
(Todd  and  Bowman.) 

Fig.  72. — Part  of  a  Striped  Muscle  Fiber  of  a  Water  Beetle  prepared  with  Absolute  Alcohol. 
A,  Sarcolemma;  B,  Krause's  membrane.  The  sarcolemma  shows  regular  bulgings.  Above  and 
below  Krause's  membrane  are  seen  the  transparent  "  lateral  discs."  The  chief  mass  of  a  muscular 
compartment  is  occupied  by  the  contractile  disc  composed  of  sarcous  elements.  The  substance  of 
the  individual  sarcous  elements  has  collected  more  at  the  extremity  than  in  the  center;  hence  this 
latter  is  more  transparent.  The  optical  effect  is  that  the  contractile  disc  appears  to  possess  a 
"median  disc"  (Disc  of  Hensen).  Several  nuclei,  C  and  D,  are  shown,  and  in  them  a  minute  net- 
work.     X  300.      (Klein  and  Noble  Smith.) 

of  those  muscles  which  are  under  the  control  of  the  will  and  hence  termed 
voluntary;  also  the  muscle  of  the  heart. 


SKELETAL     MUSCLE 


59 


For  the  sake  of  description,  striated  muscular  tissue  may  be  divided 
into  two  classes,  (a)  skeletal,  which  comprises  the  whole  of  the  striated  mus- 
cles of  the  body  except  (b)  the  heart. 

Skeletal  Muscle.  The  muscle  fibers  of  the  skeletal  muscles  are 
usually  grouped  in  small  parallel  bundles,  fasciculi.  The  fasciculi  extend 
through  the  muscle,  converging  to  their  tendinous  insertions.  Connective- 
tissue  sheaths,  endomysium,  surround  the  fasciculi  and  support  the  blood- 
vessels, while  a  stronger  sheath,  the  perimysium,  encases  the  entire  muscle. 


* 

SB 

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5J3  !  *  bs  i 
H  I  •  ■e] 

H  !  I   mi 

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C?  *     F5 

'tea    f/ifi^f 
Bffl    »V  3.  V 
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Fig.  73.— .4,  Portion  of  a  Medium-sized  Human  Muscle  Fiber.  B,  Separated  bundles  of  fibril 
equally  magnified;  a,  a,  larger,  and  b.  b,  smaller  collections;  c,  still  smaller;  d,  d,  the  smallest  which 
could  be  detached,  possibly  representing  a  single  series  of  sarcous  element.      X  800.      (Sharpey.) 


The  unit  of  muscular  structure  is  the  fiber.  Each  muscle  fiber  is  a  long 
cylinder  with  fusiform  ends.  The  fibers  vary  in  diameter  from  10  to  ioo  ix, 
while  the  length  may  reach  as  much  as  40  mm.  Each  fiber  is  enclosed  in 
a  distinct  sheath,  the  sarcolemma.  The  sarcolemma  is  a  transparent  structure- 
less sheath  of  great  resistance  which  surrounds  each  fiber,  figure  71. 

The  substance  of  the  fiber  enclosed  by  the  sarcolemma,  the  contractile 
substance,  contains  a  number  of  oval  nuclei  distributed  along  the  length  of 
the  fiber  and  lying  just  under  or  through  the  sarcolemma.  Each  nucleus  is 
accompanied  by  a  small  mass  of  granular  protoplasm  at  its  poles.  The  main 
mass  of  the  fiber  is  characterized  by  transverse  light  and  dark  bands,  figure 
73,  from  which  the  name  striated  muscle  arises. 

Longitudinal  striation  is  also  apparent  under  certain  modes  of  treat- 
ment, figure  81.  The  muscle  fibers  can  be  split  longitudinally  into  fibrils, 
called  sarcostyles,  figures  73  and  74,  each  of  which  exhibits  the  characteristic 


60 


CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


striation  of  the  whole  fiber.     Under  certain  treatment  the  sarcostyles  break 

transversely  into  smaller  discs  by  cleavage  at  the  line  of  Krause's  membrane. 

The  sarcostyle  is,  therefore,  composed  of  a  number  of  smaller  elements 

joined  end  to  end.     These  are  the  sarcous  elements  of  Bowman.     The  sar- 


Fig.  74. — Diagram  of  Segment  of  Muscle  Fiber,   showing  Sarcostyle  A,  Sarcous  element  B, 
Krause's  line  C,  Hensen's  line  D. 

cous  element  has  a  highly  refractive  denser  middle  piece  surrounded  by  a 
less  refractive  more  fluid  material.  The  polarizing  microscope  reveals  the 
fact  that  the  middle  piece  which  corresponds  in  position  to  the  dark  trans- 


mit 

mil 


Fig.  75- 


S.E. 


S.E.. 


Fig.  76. 


Fig.  75. — Sarcostyles  from  the  Wing-Muscles  of  a  Wasp.  A,  A',  Sarcostyles  showing  degrees 
of  retraction,  B.  a  sarcostyle  extended  with  the  sarcous  elements  separated  into  two  parts,  C, 
sarcostyles  moderately  extended  (semidiagrammatic).      (E.  A.  Schafer.) 

Fig.  76. — Diagram  of  a  Sarcomere  in  a  Moderately  Extended  Condition,  B.  K,K,  Krause's 
membranes;  H,  plane  of  Henson;  S,  E,  poriferous  sarcous  element.      (E.  A.  Schafer.) 

verse  band  is  doubly  refractive,  isotropic,  while  the  surrounding  material, 
the  light  band,  is  singly  refractive,  anisotropic. 


HEART     MUSCLE 


61 


In  transverse  section,  figure  70,  the  area  of  the  muscle  substance  is  mapped 
out  into  small  polygonal  areas  by  a  network  of  clear  lines  called  Cohnheim's 
areas.  The  lines  represent  the  substance  between  the  sarcostyles.  This 
substance  probably  represents  the  less  differentiated  contractile  substance, 
called  sarcoplasm.  In  figure  81  the  interfibrillar  sarcoplasm  is  indicated 
by  the  longitudinal  and  transverse  lines. 

Heart  Muscle.  The  muscle  substance  of  the  heart  is  composed 
of  mononucleated  masses  of  protoplasm,  cardiac  muscle  cells,  in  which  the 
substance  of  the  cell  presents  the  transversely  striated  appearance  char- 
acteristic of  the  voluntary  muscle  just 
described.  But  the  heart  muscle  is  phys- 
iologically much  more  like  an  involuntary 
muscle.  The  cells  are  rather  small,  two 
to  four  times  as  long  as  thick,  and  the  nu- 
cleus is  usuallv  situated  near  the  middle  of 


Fig.  77. 


Fig.  78. 


Fig.  77. — A  Section  of  Cardiac  Muscle,  Diagrammatic.  (From  E.  A.  Schafer,  after  Heiden- 
hain.) 

Fig.  78. — Intercellular  Continuity  of  Muscle  Fibrils  in  Cardiac  Muscle.  (From  E.  A.  Schafer 
after  Przewosky.) 

the  cell,  figure  79.  There  is  no  sarcolemma;  on  the  other  hand,  the  cells 
present  branched  and  irregular  outlines,  but  adjacent  cells  interlock  in 
close-fitting  contact. 

Certain  observers  have  described  fibrils  as  extending  across  the  so-called 
cell  boundary  and  noted  that  not  all  such  boundaries  enclose  nuclei.  These 
observations  suggest  that  cardiac  muscle  belongs  to  the  group  of  tissues 
possessing  a  syncytium.  However,  the  section  of  cardiac  tissue  may  very 
possibly  cut  many  cells  without  enclosing  a  nucleus.     The   continuity    of 


62 


CELL     DIFFERENTIATION     AND    THE     ELEMENTARY    TISSUES 


fibrils  is  an  important  observation  from  the  physiological  point  of  view;  see 
Circulation  Chapter. 

In  certain  parts  of  the  heart,  the  cardiac  tissue  is  not  completely  differ- 
entiated and  retains  in  the  adult  somewhat  embryonic  characters;  for  ex- 


Fig.  79. 


mSSm 


m 


Fig.  80. 


Fig.  79. — Muscular  Fiber  Cells  from  the  Heart.      (E.  A.  Schafer.) 

Fig.  80. — From  a  Preparation  of  the  Nerve  Termination  in  the  Muscular  Fibers  of  a  Snake. 
a.  End  plate  seen  o.ily  broad-surfaced:  b,  end  plate  seen  as  narrow  surface.      (Lingard  and  Klein.) 


ample,  the  bundle  of  His  running  in  the  septum  from  the  auricles  to  the 
ventricles  and  the  cells  containing  Purkinje's  fibers  lying  immediately  under 
the  endocardium. 

Blood  and  Nerve  Supply.  The  muscles  are  freely  supplied  with 
blood-vessels;  the  capillaries  form  a  network  with  oblong  meshes  around 
the  fibers.  Nerves  also  are  supplied  freely  to  muscles;  the  striated  voluntary 
muscles  receiving  them  from  the  cerebro-spinal  nerves,  and  the  cardiac 
muscle  from  both  the  cerebro-spinal  and  the  sympathetic  nerves. 

In  striped  muscle  the  nerves  end  in  motor  end-plates.  The  nerve  fibers 
are  medullated;  and  when  a  branch  passes  to  a  muscle  fiber,  its  primi- 
tive sheath  becomes  continuous  with  the  sarcolemma,  and  the  axis-cylinder 
forms  a  network  of  its  fibrils  on  the  surface  of  the  muscle  fiber.  This  net- 
work lies  embedded  in  a  flattened  granular  mass  containing  nuclei  of  several 
kinds;  this  is  the  motor  end- plate,  figures  80  and  81.  There  is  considerable 
variation  in  the  exact  form  of  the  nerve  end-plate  in  the  muscle.  In 
batrachia  the  nerve  fiber  ends  in  a  brush  of  branching  nerve  fibrils  which 
are  accompanied  here  and  there  by  attached  oval  nuclei. 

Development.  The  striated  muscle  of  the  voluntary  variety  is 
usually  developed  from  the  mesoderm.  The  embryonic  cells  increase  enor- 
mously in  size,  the  nuclei  multiply  by  fission  and  distribute  themselves  be- 
neath the  sarcolemma.     There  is  a  differentiation  of  the  cell  protoplasm 


DEVELOPMENT 


63 


which  takes  place  by  the  formation  of  sarcostyles.  This  begins  nearest  the 
surface  of  the  cells  and  proceeds  toward  the  center  of  the  mass. 

The  sarcolemma  is  apparently  produced  from  embryonic  connective 
tissue. 

The  cardiac  muscle  cells  are  at  first  spindle-shaped  embryonic  cells 
which  elongate  more  and  more.     In  further  differentiation  their  protoplasm 


Fig.  8  i. 


Fig.  82. 


Fig.  81. — Two  Striped  Muscle  Fibers  of  the  Hyoglossus  of  Frog,  a,  Nerve  end- plate;  b,  nerve 
fibers  leaving  the  end-plate;  c,  nerve-fibers  terminating  after  dividing  into  branches;  d,  a  nucleus  in 
which  two  nerve-fibers  anastomose.      X  600.      (Arndt.) 

Fig.  82. — Developing  Striated  Muscular  Fibers,  Showing  Different  Stages  of  Development  and 
Different  Positions  of  the  Unstriated  Protoplasm.  A. — Elongated  cell  with  two  nuclei;  the  longi- 
tudinal striation  is  beginning  to  show  on  the  right  side.  From  a  fetal  sheep.  (Wilson  Fox.)  B. — 
Developing  muscular  fiber,  showing  both  longitudinal  and  transverse  striations  at  the  periphery, 
and  a  central  unstriated  cylinder  of  protoplasm  containing  several  nuclei.  From  a  human  fetus 
near  the  third  month.  (Ranvier.)  n.  Nucleus  (there  is  usually  a  mass  of  glycogen  near  each 
nucleus);  p,  central  unstriated  protoplasm;  s,  peripheral  striated  substance.  C. — Developing  mus- 
cular fiber,  showing  a  lateral  position  ot  the  unstriated  protoplasm.  From  a  three-months'  human 
fetus.  (Ranvier.)  n.  Nucleus;  p,  unstriated  protoplasm  at  one  side  of  the  fiber;  s,  striated 
sarcous  substance  with  longitudinal  and  transverse  striations. 


exhibits  faint  striations  which  pervade  the  cell  as  it  grows  in  the  great  increase 
in  size.     The  rhythmic  contractions  begin  long  before  the  striations  appear. 


64 


CELL     DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


IV.     NERVOUS  TISSUE. 

Nervous  tissue  has  usually  been  described  as  being  composed  of  two 
distinct  substances,  nerve-fibers  and  nerve-cells.  The  modern  view  of  the 
nature  of  nerve  tissue  is,  however,  that  the  nerve-cell  and  the  nerve  fibers 
are  to  be  considered  together  as  one  unit,  called  the  neurone.  The  neurone 
is  embedded  in  and  supported  by  a  substance  called  neuroglia.  This  neurone 
consists  of  a  cell  body,  a  number  of  branching  processes  termed  dendrites, 
and  a  long  process  running  out  from  it,  the  neuraxone,  or  axone,  which  be- 
comes eventually  a  nerve  fiber.  The  nerve-cell  and  the  nerve  fiber  are  parts 
of  the  same  anatomical  unit,  and  the  nervous  centers  are  made  up  of  those 
units,  arranged  in  different  ways  throughout  the  nervous  system,  figure  81,  A 

NERVE    FIBERS. 

While  the  nerve  fiber  is  really  to  be  considered  as  a  process  of  the  nerve- 
cell,  it  is  convenient  to  describe  it  separately.  Nerve  fibers  are  of  two  kinds, 
medullated  or  white  fibers,  and  non-medullated  or  gray  fibers. 

Medullated  Fibers.  Each  medullated  nerve  fiber  is  made  up  of 
the  following  parts:    An  external  sheath,  called  the  primitive  sheath,  neuri- 


Fig.  83. — Diagram  Showing  the  Arrangement  of  the  Neurons  or  Nerve  Units  in  the  Architecture 
ofthe  Nervous  System.  (Raym6n  y  Cajal.)  .4,  Pyramidal  neurone  of  cerebral  cortex;  B,  anterior- 
horn  motor  cell  of  spinal  cord;  D,  collateral  branches  of  A ;  E,  medullary  neurone  with  ascending 
axone:  F,  spinal-ganglion  neurones,  G,  sensory  axones  of  F;    I,  collaterals  of  F  in  the  cord. 


MEDULLATED     NERVE     FIBRES 


65 


lemma,  or  nucleated  sheath  of  Schwann;  an  inter- 
mediate, known  as  the  medullary  or  myelin  sheath, 
or  white  substance  of  Schwann;  and  a  central  thread, 
the  axis-cylinder,  or  axial  fiber. 

The  Primitive  Sheath.  This  is  a  pellucid  mem- 
brane forming  the  outer  investment  of  the  nerve 
fiber.  The  sheath  is  constricted  at  intervals  of  a 
millimeter  or  less,  the  nodes  of  Ranvier.  Each  in- 
ternodal  segment  bears  a  single  nucleus  surrounded 
by  a  variable  amount  of  protoplasm.  This  mem- 
brane is  described  as  having  its  origin  in  the  meso- 
blastic  cells,  and  the  nuclei  are  the  indications  of  the 
cellular  nature  of  each  nodal  segment. 

The  Medullary   or   Myelin  Sheath.     This  is  the 
part  to  which  the  peculiar  opaque  white  aspect  of 
medullated   nerves    is  due.      The   thickness  of   this 
layer  of  a  nerve  fiber  varies  considerably.     It  is  a  semifluid,  fatty  substance 
of  high  refractive  power.     It  possesses  a  fine  reticulum  (Stilling,  Klein),  in 


Fig.  84. —  Two  Nerve 
Fibers  of  the  Sciatic  Nerve. 
A,  Node  of  Ranvier,  B. 
axis-cylinder;  C,  sheath 
of  Schwann,  with  nuclei. 
X  300.  (Klein  and  Noble 
Smith.) 


Fig.  85.— A  Node  of  Ranvier  in  a  Medullated  Nerve  Fiber,  viewed  from  above.  The  medul- 
lary sheath  is  interrupted,  and  the  primitive  sheath  thickened.  Copied  from  Axel  Key  and  Retzius. 
X  750.     (Klein  and  Noble  Smith.) 


Fig.  86. — Gray,  Pale,  or  Gelatinous  Nerve  Fibers.  A,  From  a  branch  of  the  olfactory  nerve 
of  the  sheep;  two  dark-bordered  or  white  fibers  from  the  fifth  pair  are  associated  with  the  pale 
olfactory  fibers ,  B,  from  the  sympathetic  nerve.      X  450.      (Max  Schultze.) 


the  meshes  of  which  is  embedded  the  fatty  material.     It  stains  well  with 
osmic  acid. 

The  Axis-Cylinder.  The  central  thread  of  a  medullated  nerve  fiber  is 

the  axis-cvlinder.     It  is  the  prolongation  of  a  nerve-cell   and  extends  un- 


6G 


CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


interrupted  for  the  full  length  of  the  fiber.  It  consists  of  a  large  number  of 
primitive  fibrilla,  as  shown  in  the  cornea,  where  the  axis-cylinders  of  nerves 
break  up  into  minute  fibrils  which  form  terminal  networks.  From  various 
considerations,  such  as  its  invariable  presence  and  unbroken  continuity  in 
all  nerves,  there  can  be  little  doubt  that  the  axis-cylinder  is  the  essential  con- 


St    w" 


Fig.  87. — Transverse  Section  of  a  Portion  of  the  Sciatic  Nerve  of  the  Rabbit.  Hardened  in 
Chromic  Acid  and  Stained  with  Picro-carmine,  to  show  medullated  fibers  in  end  view.  X  275.  a, 
Perifascicular  connective  tissue;  b,  lamellar  sheath ;  e,  axis-cylinder. 


ducting  part  of  the  fiber,  the  other  parts  having  the  subsidiary  function  of 
support  and  possibly  of  insulation. 

The  size  of  the  nerve  fibers  varies,  figure  87.  The  largest  fibers  are 
found  within  the  trunks  and  branches  of  the  spinal  nerves,  in  which  the 
majority  measure  from  14  y.  to  19  y  in  diameter.  In  the  so-called  visceral 
or  autonomic  nerves  of  the  brain  and  spinal  cord  medullated  nerves  are  found, 
the  diameter  of  which  varies  from  1.8  ,u  to  3.6  ;i.  In  the  hypoglossal  nerve 
they  are  intermediate  in  size,  and  generally  measure  7.2  /i  to  10.8  ;i. 

Non-medullated  Fibers.  The  fibers  of  the  second  kind,  figure 
86,  which  are  also  called  fibers  of  Remak,  constitute  the  principal  part  of 
the  trunk  and  branches  of  the  sympathetic  nerves,  the  whole  of  the  olfactory 
nerve,  and  are  mingled  in  various  proportions  in  the  cerebro-spinal  nerves. 
They  differ  from  the  preceding  chiefly  in  not  possessing  the  outer  layer  of 
medullary  substance;  their  contents  being  composed  exclusively  of  the  axis- 
cylinder. 

The  non-medullated  nerves  are  only  about  one-third  to  one-half  as  large 
as  the  medullated  nerves,  they  do  not  exhibit  the  double  contour,  and  they 


NERVE  TRUNKS 


67 


are   grayer  than   the   medullated   nerves.     The   non-medullated  fibers  fre- 
quently branch. 

It  is  worthy  of  note  that  in  the  fetus,  at  an  early  period  of  development, 
all  nerve  fibers  are  non-medullated. 


Fig.  88. — Transverse  Section  of  the  Sciatic  Nerve  of  a  Cat,  about  X  ioo.  It  consists  of  bundles 
(Funiculi)  of  nerve  fibers  ensheathed  in  a  fibrous  supporting  capsule,  epineurium,  A;  each  bundle 
has  a  special  sheath  (not  sufficiently  marked  out  from  the  epneurium  in  the  figure)  or  perineurium, 
B,  the  nerve  fibers,  N,  f\  L,  lymph  spaces;  A r,  artery;  V,  vein;  F,  fat.  Somewhat  diagrammatic. 
(V.  D.  Harris.) 

Nerve  Trunks.  Each  nerve  trunk  is  composed  of  a  variable  num- 
ber of  different-sized  bundles,  funiculi,  of  nerve  fibers  which  have  a  special 


Fig.  89. — Small  Branch  of  a  Motor  Nerve  of  the  Frog,  near  its  Termination,  Showing  Divis- 
ions of  the  Fibers,     a,  into  two;   b,  into  three.      X  350.     (Kolliker.) 


68  CELL     DIFFERENTIATION     AND     THE     ELEMENTARY     TISSUES 

sheath,  perineurium.  The  funiculi  are  enclosed  in  a  firm  fibrous  sheath, 
epineurium;  this  sheath  also  sends  in  processes  of  connective  tissue  which 
connect  the  bundles  together.  In  the  funiculi  between  the  fibers  is  a  delicate 
supporting  tissue,  the  endoneurium.  There  are  numerous  lymph-spaces 
both  beneath  the  connective  tissue  investing  individual  nerve  fibers  and 
also  beneath  that  which  surrounds  the  funiculi. 

Bundles  of  fibers  run  together  in  the  nerve  trunk,  but  they  merely  lie 
in  approximation  to  each  other,  they  do  not  unite.  Even  when  nerves  anas- 
tomose, there  is  no  union  of  fibers,  but  only  an  interchange  of  fibers  between 
the  anastomosing  bundles.  Although  each  nerve  fiber  is  thus  single  through 
most  of  its  course,  yet,  as  it  approaches  the  region  in  which  it  terminates,  it 
may  break  up  into  several  subdivisions  before  its  final  ending. 

Nerve  Collaterals.  It  has  been  discovered  through  the  researches 
of  Golgi,  and  confirmed  by  the  further  studies  of  Cajal  and  other  anatomists, 
that  each  individual  nerve  fiber  in  the  central  nervous  system  gives  off  in  its 


Fig.  90. — Terminal  Ramifications  of  a  Collateral  Branch  Belonging  to  a  Fiber  of  the  Posterior 
Column  in  the  Lumbar  Cord  of  an  Embryo  Calf. 

course  branches  which  pass  out  from  it  at  right  angles  for  a  short  distance, 
and  then  may  run  in  various  directions.  These  branches  are  called  collaterals. 
They  end  in  fine,  brush-like  terminations  known  as  end-brushes,  or  in  little 
bulbous  swellings  which  come  in  close  contact  with  some  nerve  cell,  figure  90. 
In  the  nerve-centers,  that  is,  in  the  brain  and  spinal  cord,  the  different 


NERVE     COLLATERALS 


09 


nerve  fibers  end  just  as  the  collaterals  do,  by  splitting  up  into  fine  branches 
which  form  the  end-brushes.  Collaterals  of  the  nerve  fibers  and  end-brushes 
are  chiefly  found  in  the  nervous  centers.  The  nerve  fibers  of  the  peripheral 
nerves  end  in  the  muscles,  glands,  or  special  sensory  organs,  such  as  the 
eye  and  ear,  each  by  its  own  special  type  of  ending.  Here,  however,  some 
analogy  to  the  end-brush  can  also  be  discovered.  As  the  peripheral  nerve 
fibers  approach  their  terminations,  they  lose  their  medullary  sheath,  and 
consist  then  merely  of  an  axis-cylinder  and  primitive  sheath.  They  may 
even  lose  the  latter,  and  only  the  axis-cylinder  be  left.  Finally,  the  axis- 
cylinder  breaks  up  into  its  elementary  fibrillae,  to  end  in  various  ways  to 
be  described  later. 


Fig.  91. 


Fig.  92. 


Fig.  91. — Nerve  Cell  with  Short  Axis-Cylinder  from  the  Posterior  Horn  of  the  Lumbar  Cord  of 
an  Embryo  Calf,  measuring  0.55  cm.      (After  Van  Gehuchten.) 

Fig.  92. — Scheme  of  Lower  Motor  Neurone.  The  cell  body,  protoplasmic  processes,  axone, 
collaterals,  and  terminal  arborizations  in  muscle  are  all  seen  to  be  parts  of  a  single  cell  and  together 
constitute  the  neurone.  (Barker.)  c.  Cytoplasm  of  cell  body  containing  chromophilic  bodies,  neuro- 
fibrils, and  perifibrillar  substance;  n,  nucleus;  n',  nucleolus;  d,  dendrites;  ah,  axone  hill  free  from 
chromophilic  bodies;  ax,  axone;  sf,  side  fibril  (collateral);  m,  medullary  sheath;  nR,  node  of 
Ranvier  where  side  branch  is  given  off;  si,  neurilemma  and  incisures  of  Schmidt;  m,  striated  mus- 
cle fiber;    iel,  motor  end  plate. 


70 


CELL     DIFFERENTIATION    AND     THE     ELEMENTARY    TISSUES 


THE  NERVE  CELL    BODY. 

The  nerve-cell  body  is  the  nodal  and  important  part  of  the  neurone,  and 
from  it  are  given  off  the  dendrites  and  axis-cylinder  process  or  axone.  It 
consists  of  a  mass  of  protoplasm,  of  varying  shape  and  size,  containing  within 


Fig.  93. — Large  Nerve  Cells  with  Processes,  from  the  Ventral  Cornua  of  the  Cord  of  Man.  X3S0. 
On  the  cell  at  the  right  two  short,  processes  of  the  cell  body  are  present,  one  or  the  other  of  which 
may  have  been  an  axis-cylinder  process  (Deiters).  A  similar  process  appears  also  on  the  cell  at 
the  left. 


Fig.  94. — Multipolar  Nerve  Cell  of  the  Cord  of  an  Embryo  Calf. 

it  a  nucleus  and  nucleolus.     All  nerve  cells  give  off  one  or  more  processes 
which  branch  out  in  various  directions,  dividing  and  subdividing  like  the 


THE    NERVE    CELL     BODY 


71 


branches  of  a  tree,  but  never  anastomosing  with  each  other  or  with  other  cells. 
These  branches  are  what  have  already  been  referred  to  as  the  dendrites  of 


- 


m 


- 

■ 


Fig.  95. — Ganglion  Cells,  Showing  Neurofibrils.     .4,  Anterior-horn  cells  of  human;   B,   cell 
from  the  facial  nucleus  of  rabbit;  C,  dendrite  of  anterior-horn  cell  of  human.     (Bethe.) 


v   m 


s» 


J' 


/ 


if       R    ^ 


^' 


Fig.  96. — Cell  of  the  Anterior  Horn  of  the  Human  Spinal  Cord,  Stained  by  Nissl's  Method, 
showing  chromophiles.      (After  Edinger.) 

the  cell.  They  were  formerly  called  the  protoplasmic  processes,  figures  91, 
93.  It  is  thus  seen  that  the  neurone  or  nerve  unit  consists  of  a  number  of 
subdivisions,    namely,    the   cell  body,   with   its   nucleus  and   nucleolus,  the 


72 


CELL    DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


dendrites  or  protoplasmic  processes,  and  the  axone  or  axis-cylinder  process, 
which  forms  what  is  known  as  a  nerve  fiber. 

The  protoplasm  of  the  cells  is  shown  by  various  dyes  to  consist  of  neuro- 
fibrils, perifibrillar  substance,  and  in  most  cells  chromophilic  bodies.  Apathy 
and  others  have  demonstrated  that  a  network  of  interlacing  and  anasto- 
mosing fibrils  traverses  both  the  cell  body  and  its  branches,  figure  95. 


Fig.  97. — An  Isolated  Sympathetic  Ganglion  Cell  of  Man,  Showing  Sheath  with  Nucleated  Cell 
Lining,  B.  A,  Ganglion  cell,  with  nucleus  and  nucleolus;  C,  branched  process  or  dendrite,  D, 
unbranched  process  or  axone.      (Key  and  Retzius.)      X  75°- 

The  perifibrillar  substance  is  a  fluid  or  semifluid  substance  in  which  the 
fibrils  are  embedded.  By  treating  nerve-cells  with  special  stains  granular 
bodies  of  varying  size  are  found  embedded  in  the  cytoplasm.  These  bodies 
are  the  chromophilic  bodies,  figure  96. 

Ganglion  cells  are  generally  enclosed  in  a  transparent  membranous 
capsule  similar  in  appearance  to  the  external  nucleated  sheath  of  nerve- 
fibers;    within  this  capsule  is  a  layer  of  small  flattened  cells. 


Nerve  Terminations. 

Nerve  fibers  terminate  peripherally  in  four  different  ways.  1,  by  the  ter- 
minal subdivisions  which  pass  in  between  epithelial  cells,  and  are  known 
as  inter-epithelial  arborizations;  2,  by  motor-plates  which  lie  in  the  muscles; 
3,  by  special  end-organs,  connected  with  the  senses  of  sight,  hearing,  smell, 
and  taste;    and,  4,  by  various  forms  of  tactile  corpuscles. 

The  Inter-epithelial  Arborizations.  This  forms  a  most  common 
mode  of  termination  of  the  sensory  nerves  of  the  body.     The  nerve  fibers 


THE    INTER-EPITHELIAL    ARBORIZATIONS 


73 


to  the  surface  of  the  skin  or  mucous  membrane  lose  their  neurilemma  and 
myelin  sheath,  the  bare  axis-cylinder  divides  and  subdivides  into  minute 
ramifications  among  the  epithelial  cells  of  the  skin  and  mucous  membrane. 
In  the  various  glands  of  the  body  this  form  of  termination  also  prevails. 


Fig.  98. — Sensory-Nerve    Terminations    in   Stratified  Pavement  Epithelium.     Golgi's    rapid 
method.      (After  G.  Retzius.) 

The  hair-bulbs,  the  teeth,  and  the  tendons  of  the  body  are  supplied  by  this 
same  process  of  terminal  arborization,  figures  98,  99. 

The  motor  nerves  to  the  muscles  end  in  what  are  known  as  muscle- plates, 
the  details  of  whose  structure  have  been  already  described. 

The  special  sensory  end-organs  will  be  described  later  in  the  chapter 
on  the  Special  Senses. 

A  fourth  form  of  termination  consists  of  corpuscles  that  are  more  or  less 
encapsulated,  and  these  are  known  as  the  corpuscles  of  Pacini,  the  tactile 


Fig.  99. — Sensory'- Nerve  Termination  in  the  Epithelium  of  the  Mucosa  of  the  Inferior  Vocal 
Cord  and  in  the  Ciliated  Epithelium  of  the  Subglottic  Region  of  the  Larynx  of  a  Cat  Four  Weeks  Old. 
(After  G.  Retzius.)  Golgi's  rapid  method,  n.  Nerve-fibers  rising  from  the  connective-tissue  layer 
into  the  epithelial  layer,  where  they  terminate  in  ramified  and  free  arborizations. 

corpuscles  0}  Meissner,  the  tactile  corpuscles  of  Krause,  the  tactile  menisques, 
and  the  corpuscles  of  Golgi. 

The  Pacinian  Corpuscles.  These  nerve  endings,  named  after 
their  discoverer  Pacini,  are  elongated  oval  bodies  situated  on  some  of  the 
cerebro-spinal  and  sympathetic  nerves.  They  occur  on  the  cutaneous 
nerves  of  the  hands  and  feet,  the  branches  of  the  large  sympathetic  plexus 
about  the  abdominal  aorta,  the  nerves  of  the  mesentery,  and  have  been 
observed  also  in  the  pancreas,  lymphatic  glands,  and  thyroid  glands,  figure  100. 
Each  corpuscle  is  attached  by  a  narrow  pedicle  to  the  nerve  on  which  it  is 
situated,  and  is  formed  of  several  concentric  layers  of  fine  membrane,  each 


74 


CELL     DIFFERENTIATION     AND     THE     ELEMENTARY    TISSUES 


layer  being  lined  by  endothelium,  figure  ioo.     A  single  nerve  fiber  passes 
through  its  pedicle,  traverses  the  several  concentric  layers,  enters  a  central 
cavity,  and  terminates  in  a  knob-like  enlargement  or  in  a  bifurcation. 
The  physiological  import  of  these  bodies  is  still  obscure. 


Fig. 


Fig.  ioi. 


Fig.  ioo. — Pacinian  Corpuscle  of  the  Cat's  Mesentery.  The  stalk  consists  of  a  nerve  fiber,  n, 
with  its  thick  outer  sheath.  The  peripheral  capsules  of  the  Pacinian  corpuscle  are  continuous 
with  the  outer  sheath  of  the  stalk.  The  intermediary  part  becomes  much  narrower  near  the  en- 
trance of  the  axis-cylinder  into  the  clear  central  mass.  A  hook-shaped  termination  with  the  end- 
bulb,  a,  is  seen  in  the  upper  part.      (Ranvier.) 

Fig.  ioi. — Summit  of  a  Pacinian  Corpuscle  of  the  Human  Finger,  showing  the  Endothelial 
Membranes  Lining  the  Capsules.      X  220.      (Klein  and  Noble  Smith.) 


The  Tactile  Corpuscles  of  Meissner.  They  are  found  in  the  papillae 
of  the  skin  of  the  fingers  and  toes,  or  among  its  epithelium.  When  simple 
they  are  small,  slightly  flattened  transparent  bodies  composed  of  nucleated 
cells  enclosed  in  a  capsule.  When  compound,  the  capsule  contains  several 
small  cells.  The  nerve  fiber  penetrates  the  corpuscles,  loses  its  myelin 
sheath,  and  divides  and  subdivides  to  form  a  series  of  arborizations.  The 
terminal  arborizations  occupy  the  central  part  of  the  corpuscle,  and  are 
surrounded  by  a  great  number  of  marginal  cells.  The  touch  or  tactile 
corpuscles  of  Meissner  have  been  regarded  at  one  time  as  epithelial,  at 
another  time  as  nervous,  but  they  are  to-day  proved  to  be  mesodermic  cells, 
and  differentiated  for  the  special  purpose  of  the  sense  of   touch  (Dejerine). 

The  Corpuscles  of  Krause  or  End-Bulbs.  These  exist  in  great 
numbers  in  the  conjunctiva,  the  glans  penis,  clitoris,  lips,  skin,  and  in  tendon 
of  man.  They  resemble  the  corpuscles  of  Pacini,  but  have  much  fewer 
concentric  layers  to  the  corpuscle,  and  contain  a  relatively  voluminous  central 


TACTILE     MENISQUES 


75 


mass  composed  of  polyhedral  cells.  In  man  these  corpuscles  are  spherical 
in  shape,  and  receive  many  nerve  fibers  which  wind  through  the  corpuscles 
and  end  in  the  free  extremities,  figure  103. 


Fig.  102. — Tactile  Corpuscle  of  Meissr.er,  Tactile  Cell  and  Freo  Nerve  Ending.  (Merkel- 
Kenle.)  o,  Corpuscle  proper,  outside  of  which  is  seen  the  connective-tissue  capsule;  b,  fiber  end- 
ing on  tactile  cell;   c,  fiber  ending  freely  among  the  epithelial  cells. 

Tactile  Menisques.  In  different  regions  of  the  skin  of  man,  one 
meets,  in  the  superficial  layers  and  in  the  Malpighian  layers,  nerves 
which,  after  having  lost  their  myelin  sheath,  divide  and  subdivide  to  form 


Fig.  103. 


Fig.  104. 


Fig.  103. — End-Bulb  of  Krause.     a,  Medullated  nerve  fiber;    b,  capsule  of  corpuscle. 
Fig.  104. — A  Termination  of  a  Medullated  Nerve  Fiber  in  Tendon,  lower  half  with  Convoluted 
Medullated  Nerve  Fiber.     (Golgi.) 

extremely  beautiful  arborizations.  The  branches  of  these  arborizations 
are  the  tactile  menisques.  These  menisques,  which  simulate  the  form  of  a 
leaf,  represent  a  mode  of  terminal  nervous  arborization  (Ranvier). 


70 


CELL    DIFFERENTIATION     AND     THE    ELEMENTARY    TISSUES 


The  Corpuscles  of  Golgi.     These  are  small  terminal  plaques  placed 
at  the  union  of  tendons  and  muscles,  but  belonging  more  properly  to  the 


Fig.  105. — Neuroglia  Cells  in  the  Cord  of  an  Adult  Frog.  (After  CI.  Sala.)  .4,  Ependyma 
cells  with  their  peripheral  extremities  atrophied  and  ramified;  B,  C,  D,  neuroglia  cells  in  different 
degrees  of  emigration  and  separation  from  the  ependymal  canal;  their  central  extremity  is  atro- 
phied and  much  contracted;  their  peripheral  extremity,  on  the  other  hand,  is  greatly  extended; 
the  ramifications  of  the  latter,  terminating  in  conical  buttons,  /,  end  under  the  pia  mater. 


Fig.  106. — Different  Types  of  Neuroglia  Cells.     (After  Van  Gehuchten.)     b.  Neuroglia  cells  of 
the  white  substance,  and  c,  of  the  gray  substance  of  the  cord  of  an  embryo  calf. 


THE     NEUROGLIA  77 

tendon.  They  are  fusiform  in  shape  and  are  flattened  upon  the  surface  of 
the  tendon  close  to  its  insertion  into  the  muscular  fibers.  They  are  composed 
of  a  granular  substance,  enveloped  in  several  concentric  hyaline  membranes 
which  contain  some  nuclei.  The  nerve  fiber  passes  into  this  little  corpuscle, 
splitting  itself  up  into  fine  terminals.  The  corpuscles  of  Golgi  are  believed 
to  be  related  to  the  muscular  sense,  figure  104. 

THE    NEUROGLIA. 

The  neuroglia,  while  not  a  nervous  tissue,  is  closely  mingled  with  it  and 
forms  an  important  constituent  of  the  nervous  system.  It  consists  of  cells 
giving  off  a  fine  network  of  richly  branching  fibers.  Neuroglia  is  a  form 
of  connective  tissue,  and  it  is  in  its  functions  strictly  comparable  to  the  con- 
nective tissue  which  supports  the  special  structures  of  other  organs,  like  the 
lungs  and  kidneys,  figure  106.  In  the  adult  animal  the  neuroglia-tissue  is 
composed  of  cells  from  which  are  given  off  immense  numbers  of  fine  processes. 
These  extend  out  in  every  direction,  and  intertwine  among  the  nerve-fibers 
and  nerve-cells,  figure  105.  The  neuroglia  cell  differs  in  size  and  shape 
very  much  in  different  parts  of  the  nervous  system  in  accordance  with  the 
arrangement  of  the  nervous  structures  about  it.  The  cell  is  composed  of 
granular  protoplasm,  and  lying  in  it  is  a  large  nucleus,  within  which  is  a 
nucleolus.     The  body  of  the  cell  is  small  in  proportion  to  the  nucleus. 


CHAPTER    III 

THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

Of  the  eighty  chemical  elements  which  have  been  isolated,  no  less  than 
seventeen  combine  in  varying  quantities  to  form  the  chemical  basis  of  the 
animal  body.  The  substances  which  contribute  the  largest  share  are  the 
non-metallic  elements,  Oxygen,  Carbon,  Hydrogen,  and  Nitrogen — oxygen 
and  carbon  making  up  altogether  about  85  per  cent  of  the  whole.  The  most 
abundant  of  the  metallic  elements  are  Calcium,  Sodium,  and  Potassium  * 

These  elements  do  not  exist  in  the  animal  body  in  the  free  state,  but  are 
combined  into  complex  chemical  compounds.  Of  course  we  cannot  analyze 
the  living  protoplasm  and  isolate  its  compounds. 

The  first  step  in  the  act  of  separating  the  composition  products  of  proto- 
plasm produces  changes  which  destroy  the  chemical  and  physical  relations 
of  these  products  which  maintain  the  state  of  life.  Dead  protoplasm,  how- 
ever, yields  a  number  of  substances  which  must  be  very  directly  derived 
from  the  living  protoplasm.  On  the  other  hand,  certain  products  can  be 
isolated  from  the  animal  body  which  are  evidently  not  a  part  of  the  proto- 
plasm itself,  but  products  of  protoplasmic  activity.  Some  of  these,  like  fat, 
glycogen,  etc.,  are  constructive  products,  others  are  disintegration  products 
of  protoplasmic  activity. 

A  large  number  of  the  animal  compounds,  particularly  those  of  the  nitrog- 
enous group,  are  characterized  by  their  complexity.  Many  elements  enter 
into  their  composition,  and  many  atoms  of  the  same  element  occur  in  each 
molecule.     This  latter  fact  no  doubt  explains  the  reason  of  their  instability. 

Of  the  numerous  compounds  that  have  been  isolated  from  the  animal 
body,  only  a  very  few  of  the  most  important  will  be  discussed  in  this  chapter. 

*The  following  table  represents  the  relative  proportion  of  the  various  elements  in 
the  body.     (Marshall.) 

Oxygen 72.0 

Carbon 13.5 

Hydrogen 9.1 

Nitrogen 2.5 

Calcium 1.3 

Phosphorus 1.15 

Sulphur. . , 0.1476 

Sodium 0.1 

Chlorine 0.085 


Fluorine 0.08 

Potassium 0.026 

Iron 0.01 

Magnesium 0.0012 

Silicon 0.0002 

(Traces  of  copper,   lead,   and   alu- 
minum)      


78 


THE    NITROGENOUS    BODIES  79 


THE    NITROGENOUS    BODIES. 


Nitrogenous  bodies  take  the  chief  part  in  forming  the  solid  tissues  of  the 
body,  and  are  found  also  to  a  considerable  extent  in  the  circulating  fluids 
(blood,  lymph,  chyle),  the  secretions  and  excretions.  They  often  contain, 
in  addition  to  carbon,  hydrogen,  nitrogen,  and  oxygen,  the  elements  sulphur 
and  phosphorus;  but  although  the  composition  of  most  of  them  is  approxi- 
mately known,  no  general  rational  formula  can  at  present  be  given  for  the 
proteids. 

Proteids.  The  nitrogenous  substances  constitute  the  most  im- 
portant and  complex  compounds  of  the  body.  According  to  their  chemi- 
cal composition  and  reactions  they  are  divided  into  three  main  classes,  viz., 
i,  simple  proteids;    2,  compound  proteids;   and  3,  albuminoids. 

The  proteids  are  the  chief  of  the  nitrogenous  organic  compounds  and 
exist  in  both  plants  and  animals,  one  or  more  of  them  entering  as  r-n  essential 
part  into  the  formation  of  all  living  tissue.  They  exist  abundantly  in  the 
lvmph,  chvle,  and  blood.  Very  little  is  known  with  any  certainty  about 
their  exact  chemical  composition.  Their  formulae  are  unknown,  the  chem- 
ists who  have  attempted  to  construct  the  structural  formulae  differing  very 
greatly  among  themselves.  In  fact  the  very  term  proteid  is  an  extremely 
arbitrary  one.  It  simply  means  a  body  which,  according  to  Hoppe-Seyler, 
contains  in  its  molecule  the  -elements  carbon,  hydrogen,  nitrogen,  oxygen, 
and  sulphur,  in  certain  arbitrary  but  varying  amounts,  thus — Carbon,  from 
51.5  to  54.5;  Hydrogen,  from  6.9  to  7.3;  Nitrogen,  from  15.2  to  17;  Oxy- 
gen, from  20.9  to  23.5;  Sulphur,  from  0.3  to  2.  Some  proteids  contain  from 
0.8  to  4.5  per  cent  of  phosphorus;  a  small  amount  of  iron  is  usually  associ- 
ated with  proteids,  but  it  is  not  certain  whether  or  not  it  is  an  integral  part 
of  the  molecule.  Chittenden  defines  a  proteid  as  a  substance  which  con- 
tains carbon,  hydrogen,  oxygen,  nitrogen,  and  sulphur,  the  nitrogen  being 
in  a  form  which  serves  the  physiological  needs  of  the  body;  and  yields,  on 
decomposition,  a  row  of  crystalline  amido-acids  and  crystalline  nitrogenous 
bases;   nearly  all  contain  52  per  cent  of  carbon  and  16  per  cent  of  nitrogen. 

Properties  of  Proteids.  Proteids  are  for  the  most  part  amorph- 
ous and  non-crystallizable.  Certain  of  the  vegetable  proteids  have  been 
crystallized,  and  according  to  Hofmeister,  egg  albumin  is  also  capable  of 
crystallization.  They  possess  as  a  rule  no  power  (or  scarcely  any)  of  passing 
through  animal  membranes.  They  are  soluble,  but  undergo  alteration  in 
composition  in  strong  acids  and  alkalies;  some  are  soluble  in  water,  others 
in  neutral  saline  solutions,  some  in  dilute  acids  and  alkalies,  none  in  alcohol 
or  ether.     Their  solutions  exercise  a  left-handed  rotation  on  polarized  light. 

The  hope  that  it  may  be  possible  in  the  immediate  future  to  synthesize 
proteids  is  not  very  great,  because  of  the  extraordinary  variety  of  compounds 
obtained  by  the  decomposition  of  proteids  by  various  chemical  methods, 


80  THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

the  compounds  differing  according  to  the  method  employed.  In  the  body 
it  seems  clear  that  living  proteid  is  built  up  by  the  food  supplied  to  it,  which 
necessarily  contains  proteid  derived  from  either  a  vegetable  or  an  animal 
source;  how  this  process  takes  place  we  are  yet  unable  to  say.  Recently 
Taylor  has  been  able  to  synthesize  proteid,  protamin,  by  the  reversible 
action  of  trypsin  on  the  amido-acids  which  were  previously  obtained  by  the 
digestion  of  protamin.     The  reaction  is  indicated  by  the  equation: 

Protein  -j-  Water  <=±  Amido-acids. 

Robertson  has  demonstrated  a  similar  reversible  reaction  of  pepsin  on  para- 
nuclei derived  from  the  digestion  of  casein.  These  experiments  lend  a  new 
stimulus  to  the  efforts  to  build  up  proteids  in  the  chemical  laboratory  along 
the  lines  of  catalytic  action  of  enzymes. 

In  the  course  of  later  chapters  in  this  book  we  shall  endeavor  to  trace 
the  steps  of  the  breaking  up  of  proteid  in  the  body,  but  we  may  anticipate 
by  mentioning  that  it  is  now  generally  believed  that  the  chief  ultimate  prod- 
ucts of  this  decomposition  are  urea,  a  body  the  formula  of  which  is 
CO  (NH  )  ,  carbon  dioxide  and  water,  while  the  intermediate  substances  or 
by-products  are  chiefly  ammonia  compounds.  When  proteid  material  is 
decomposed  by  putrefaction,  by  the  action  of  chemical  reagents,  acids,  alka- 
lies, or  by  heat,  various  bodies  are  produced,  of  which  amido-acids  (acids 
in  which  one  or  more  of  the  hydrogen  atoms  of  the  radical  of  the  acid  are 
replaced  by  amidogen,  NH  )  and  bodies  belonging  to  the  aromatic  or  benzene 
series  predominate.  Hence  it  comes  that  various  theories  of  the  way  in 
which  proteids  are  built  up  have  arisen.  The  one  which  has  appeared  to 
have  received  the  greatest  support  is  that  of  Latham.  This  observer  has 
suggested  that  proteid  may  be  considered  as  made  up  of  a  series  of  cyan- 
alcohols  (bodies  obtained  by  the  union  of  any  aldehyde  with  hydrocyanic 
acid)  with  a  benzene  nucleus.  Taking  ordinary  ethyl  alcohol,  CH3CH  OH, 
as  the  type,  the  aldehyde  of  which  is  CH3CHO,  the  corresponding  cyan- 
alcohol  would  be  CH3CHCNOH. 

CLASSES    OF    PROTEIDS. 
Simple  Proteids. 

Native  Albumins. 

Albumins;   serum  albumins,  egg  albumins,  lactalbumin. 

Globulins ;   serum  globulin,  myosinogen,  cytoglobulin,  etc. 
Derived  Albumins. 

Albuminates ;   acid  and  alkali  albumins. 

Coagulated  proteids  ;  heat  coagulated  and  enzyme  coagulated  proteid. 

Proteose,   Peptones,   Polypeptids ;    all  derived  as  cleavage-products 
of  enzyme  action  on  other  proteids. 


PROTEIDS  81 

Histons  ;  contain  35  to  42  per  cent  of  their  nitrogen  as  basi  *  nitrogen. 

Protamins;  contain  63  to  88  per  cent  of  their  nitrogen  as  basic  nitro- 
gen. 
Compound  Proteids. 

Hemoglobin  ;  decomposes  into  a  proteid  and  a  chromogen. 

Nucleo  proteid;  decomposes  into  a  proteid  and  nucleic  acid. 

Glyco proteid;   decomposes  into  a  proteid  and  a  reducing  substance, 
mucin. 
Albuminoid  substances;    mucin,  keratin,  albumoid,  collagen,  elastin, 
etc. 

The  Albumins.  Of  native  albumins  there  are  several  varieties: 
egg  albumin;    serum  albumin;    lact  albumin,  etc. 

When  in  solution  in  water  it  is  a  transparent,  frothy,  yellowish  fluid, 
neutral  or  slightly  alkaline  in  reaction.  It  gives  all  of  the  general  proteid 
reactions.  On  digestion  it  yields  8  per  cent  of  argenin,  22.6  per  cent  of 
leucin,  and  2  per  cent  of  tyrosin. 

At  a  temperature  not  exceeding  400  C.  it  is  dried  up  into  a  yellowish, 
transparent,  glassy  mass,  soluble  in  water.  At  a  temperature  of  700  C.  it  is 
coagulated  into  a  new  substance,  coagulated  proteid,  which  is  quite  insoluble 
in  water.  It  is  coagulated  also  by  the  prolonged  action  of  alcohol;  by  strong 
mineral  acids,  especially  by  nitric  acid;  also  by  tannic  acid,  or  carbolic  acid; 
and  by  ethers.     The  coagulum  is  soluble  in  caustic  soda. 

With  strong  nitric  acid  the  albumin  is  precipitated  at  the  point  of  contact 
with  the  acid  in  the  form  of  a  fine  white  or  yellow  ring. 

Serum  Albumin  is  contained  in  blood  serum,  lymph,  serous  and  synovial 
fluids,  and  in  the  tissues  generally;  it  may  be  prepared  from  serum  after 
removal  of  paraglobulin,  by  a  saturation  with  sodium  sulphate.  It  appears 
in  the  urine  in  the  pathological  condition  known  as  albuminuria. 

It  gives  similar  reactions  to  egg  albumin,  but  differs  from  it  in  not  being 
coagulated  by  ether.  It  also  differs  from  egg  albumin  in  not  being  easily 
precipitated  by  hydrochloric  acid,  and  in  the  precipitate  being  easily  soluble 
in  excess  of  that  acid.  Serum  albumin,  either  in  the  coagulated  or  precipi- 
tated form,  is  more  soluble  in  excess  of  strong  acid  than  egg  albumin. 

Globulins.  Globulins  are  found  in  egg;  in  blood,  lymph,  and 
other  body  fluids;   and  in  most  protoplasm. 

The  globulins  give  the  general  proteid  tests;  are  insoluble  in  water;  are 
soluble  in  dilute  saline  solutions;  are  soluble  in  acids  and  alkalies  forming 
the  corresponding  derived  albumin. 

Most  of  them  are  precipitated  from  their  solutions  by  saturation  with 
solid  sodium  chloride,  magnesium  sulphate,  or  other  neutral  salt.  They 
are  coagulated,  but  at  different  temperatures,  on  heating. 

A  globulin  is  obtained  from  the  crystalline  lens  by  rubbing  it  up  with 
6 


82  THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

powdered  glass,  extracting  with  dilute  saline  solution,  and  by  passing  through 
the  extract  a  stream  of  carbon  dioxide.  It  differs  from  other  globulins  in 
not  being  precipitated  by  saturation  with  sodium  chloride. 

The  globulin,  myosin,  may  be  prepared  from  muscle  by  removing  all 
fat,  tendon,  etc.,  and  washing  repeatedly  in  water  until  the  washing  con- 
tains no  trace  of  proteids,  mincing  it,  and  then  treating  with  10  per  cent  solu- 
tion of  sodium  chloride,  or  similar  solution  of  ammonium  chloride  or  magne- 
sium sulphate.  The  salt  solution  will  dissolve  a  large  portion  into  a  viscid 
fluid,  which  filters  with  difficulty.  If  the  viscid  filtrate  be  dropped  little  by 
little  into  a  large  quantity  of  distilled  water,  a  white  flocculent  precipitate 
of  myosin  will  occur. 

Myosin  is  soluble  in  10  per  cent  saline  solution;  it  is  coagulated  at  6o°  C. 
into  coagulated  proteid;  it  is  soluble  without  change  in  very  dilute  acids; 
it  is  precipitated  by  picric  acid,  the  precipitate  being  redissolved  on  boiling; 
it  may  give  a  blue  color  with  ozonic  ether  and  tincture  of  guaiacum. 

Serum  globulin  is  contained  in  plasma  and  in  serum,  in  serous  and  syno- 
vial fluids,  and  may  be  precipitated  by  saturating  plasma  after  removal  of 
fibrinogen,  or  by  saturating  serum  with  solid  sodium  chloride  or  magne- 
sium sulphate.  Globulin  separates  as  a  bulky  flocculent  substance  which 
can  be  removed  by  filtration.  It  may  also  be  prepared  by  diluting  blood- 
serum  with  ten  volumes  of  water,  and  passing  carbonic-acid  gas  rapidly 
through  it.  The  fine  precipitate  may  be  collected  on  a  filter,  and  washed 
with  water  containing  carbonic-acid  gas.  It  is  very  soluble  in  dilute  saline 
solutions,  5  to  8  per  cent,  from  which  it  is  precipitated  by  carbonic-acid  gas 
or  by  dilute  acids.  Its  solution  is  coagulated  at  7  20  C.  Dilute  acids  and 
alkalies  convert  it  into  acid  or  alkali  albumin. 

Fibrinogen  is  contained  in  blood  plasma,  from  which  it  may  be  prepared 
by  the  addition  of  sodium  chloride  to  the  extent  of  13  per  cent.  It  may 
also  be  prepared  from  hydrocele  fluid  or  from  other  serous  transudation  by 
a  similar  method.  Its  general  reactions  are  similar  to  those  of  paraglobulin. 
But  its  solution  is  coagulated  at  55°-56°  C.  Its  characteristic  property 
consists  in  the  facility  with  which  it  forms  the  insoluble  proteid  fibrin. 

Edestin  is  a  globulin  which  is  found  in  many  edible  vegetables,  grain, 
etc.  A  solution  may  be  prepared  by  adding  hempseed  to  a  10  per  cent 
solution  of  sodium  chloride  and  heating  to  500  C. 

Albuminates.  There  are  two  principal  substances  belonging  to 
this  class:  a,  acid  albumin;   b,  alkali  albumin. 

Acid  Albumin.  Acid  albumin  is  made  by  adding  small  quantities  of 
dilute  acid  (of  which  the  best  is  hydrochloric,  0.4  to  1  per  cent)  to  either 
egg  or  serum  albumin  diluted  with  five  to  ten  times  its  bulk  of  water,  and 
keeping  the  solution  at  a  temperature  not  higher  than  500  C.  for  not  less  than 
half  an  hour.  It  may  also  be  made  by  dissolving  coagulated  native  albumin 
in  strong  acid,  or  by  dissolving  any  of  the  globulins  in  acids.     Solid  acid 


COAGULATED   PROTEIDS  83 

albuminate  may  be  formed  by  adding  strong  acid  drop  by  drop  to  a  strong 
solution  of  proteid  matter  (e.g.,  undiluted  egg  albumin)  until  solidifica- 
tion occurs. 

It  is  not  coagulated  on  heating,  but  on  exactly  neutralizing  the  solution 
a  flocculent  precipitate  is  produced;  if  it  is  then  heated  to  700  C.  it  will  co- 
agulate and  cannot  then  be  distinguished  from  any  other  form  of  coagu- 
lated proteids.  This  may  be  shown  by  adding  to  the  acid  albumin  solution 
a  little  aqueous  solution  of  litmus  and  then  adding,  drop  by  drop,  a  weak 
solution  of  caustic  potash  from  a  buret  until  the  red  color  disappears.  The 
precipitate  is  the  derived  albumin.  It  is  soluble  in  dilute  acid,  dilute  alka- 
lies, and  dilute  solutions  of  alkaline  carbonates.  The  solution  of  acid 
albumin  gives  the  proteid  tests.  The  substance  itself  is  coagulated  by  strong 
acids,  e.g.,  nitric  acid,  and  by  strong  alcohol;  it  is  insoluble  in  distilled  water, 
and  in  neutral  saline  solutions;  it  is  precipitated  from  its  solutions  by  satura- 
tion with  sodium  chloride.  On  boiling  in  lime-water  it  is  partially  coagu- 
lated, and  a  further  precipitation  takes  place  on  addition  to  the  boiled  solu- 
tion of  calcium  chloride,  magnesium  sulphate,  or  sodium  chloride. 

Alkali  Albumin.  If  solutions  of  native  albumin,  or  coagulated  albu- 
min, or  other  proteid  be  treated  with  dilute  or  strong  fixed  alkali,  alkali 
albumin  is  produced.  Solid  alkali  albumin  (Lieberkuhn's  jelly)  may  also 
be  prepared  by  adding  caustic  soda  or  potash,  drop  by  drop,  to  undiluted 
egg  albumin,  until  the  whole  forms  a  jelly.  This  jelly  is  soluble  in  an  excess 
of  the  alkali  or  in  dilute  alkalies  on  boiling.  A  solution  of  alkali  albumin 
gives  the  tests  corresponding  to  those  of  acid  albumin.  It  is  not  coagulated 
on  heating  except  after  neutralization,  as  in  the  case  of  acid  albumin.  It 
is  thrown  down  on  neutralizing  its  solution,  except  in  the  presence  of  alkaline 
phosphates,  in  which  case  the  solution  must  be  distinctly  acid  before  a  pre- 
cipitate falls. 

To  differentiate  between  acid  and  alkali  albumin,  the  following  method 
may  be  adopted:  Alkali  albumin  is  not  precipitated  on  exact  neutralization 
if  sodium  phosphate  has  been  previously  added.  Acid  albumin  is  precipi- 
tated on  exact  neutralization,  whether  or  not  sodium  phosphate  has  been 
previously  added. 

Coagulated  Proteids.  These  are  formed  by  the  action  of  heat 
or  of  ferments  upon  other  proteids;  the  temperature  necessary  to  produce 
coagulation  varying  in  the  manner  previously  indicated.  They  may  also 
be  produced  by  the  prolonged  action  of  alcohol  upon  proteids;  the  process 
is  one  of  dehydration.  They  are  soluble  in  strong  acids  or  alkalies;  slightly 
so  in  dilute;  are  soluble  in  digestive  fluids  (gastric  and  pancreatic),  and  are 
insoluble  in  water  or  saline  solutions  (except  fibrin). 

Fibrin  is  formed  by  the  action  of  fibrin  ferment  on  fibrinogen  and  can  be 
obtained  as  a  soft,  white,  fibrous,  and  very  elastic  substance  by  whipping 
blood  with  a  bundle  of  twigs  and  washing  the  adhering  mass  in  a  stream  of 


84  THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

water  unto  all  the  blood-coloring  matter  is  removed.  It  is  soluble  to  a  cer- 
tain extent  in  strong  sodium-chloride  solutions. 

Proteoses.  These  are  intermediate  substances  of  the  digestion 
of  other  proteids,  the  ultimate  product  of  which  is  peptone  or  lower  cleavage 
products.  They  are  produced  by  the  action  of  the  gastric  and  pancreatic 
juices  and  also,  slowly,  by  boiling  with  dilute  acids.  The  term  is  a  general 
one,  the  proteose  of  albumin  being  albumose,  that  of  globulin  being  globu- 
lose,  etc.  They  are  divided  into  primary  and  secondary  groups  representing 
the  stages  of  progression  from  proteids  to  peptones,  so  that  there  may  be  a 
primary  and  a  secondary  albumose,  etc.  As  digestion  is  a  process  of  hydra- 
tion with  cleavage,  the  successive  stages  present  progressively  simpler  sub- 
stances. Each  group  reacts  to  fewer  reagents  than  the  preceding  one;  e.g., 
none  of  the  proteoses  can  be  coagulated  by  boiling.  Nitric  acid  will  precipi- 
tate the  primary  proteoses  but  not  the  secondary  ones. 

Peptones.  Peptone  is  formed  by  the  action  of  the  digestive  fer- 
ments, pepsin  or  trypsin,  on  other  proteids,  and  on  gelatin.  It  is  a  still 
simpler  form  of  substance  than  the  proteoses  and  reacts  to  still  fewer  reagents. 
Peptones  will  be  considered  in  connection  with  the  physiology  of  digestion, 
as  will  also  be  the  intermediate  compounds. 

Histons.  Histons  are  decomposition  products  but  present  well- 
defined  proteid  reactions.  They  are  strongly  basic  and  have  a  large  con- 
tent of  hexon  bases.  Histons  are  soluble  in  water;  are  precipitated  by  weak 
ammonia;  are  soluble  in  acids;  do  not  coagulate  by  heat  in  water  solutions 
unless  salts  are  present.  They  are  not  changed  by  and  may  be  recovered 
from  the  salt  heat  coagulation.  They  do  not  contain  phosphorus.  They 
give  the  biuret  reaction,  but  do  not  give  Millon's  reaction. 

Protamin.  This  substance  is  of  special  interest  in  that  it  is  the 
simplest  of  the  proteids.  It  is  a  cleavage  product  which  exists  in  nature  in 
fish  sperm  as  a  nucleic  acid  compound.  It  gives  the  biuret  but  not  Millon's 
reaction,  is  not  coagulated  by  heat.  It  yields  amido-acids  as  cleavage-prod- 
ucts. These  cleavage-products  have  been  recently  resynthesized  by  Taylor 
by  the  action  of  trypsin. 

Compound  Proteids.  The  compound  proteids  are  compounds 
of  a  simple  proteid  with  some  other  molecule.  According  to  their  chemical 
composition  and  characteristics  they  are  divided  into  several  classes,  viz.: 
Chromoproteids.  This  is  a  combination  of  a  proteid  substance  with  some 
form  of  pigment.  For  example,  hemoglobin  is  a  combination  of  a  globulin 
with  hematin,  an  iron-containing  radicle.  Hemoglobin  is  described  more 
fully  in  the  chapter  on  the  Blood.  Nncleo proteids.  Nucleoproteids  are  a 
combination  of  a  proteid  substance  with  a  nucleic  acid;  they  are  divided 
into  two  groups  according  to  the  character  of  the  acid.  The  true  nucleo- 
proteids contain  true  nucleic  acid*,  the  para -nucleoproteids  or  pseudo-nucleo- 
proteids  contain  para-nucleic  acid.     Both  acids,  and  therefore  both  groups, 


MUCIN  85 

contain  phosphorus;  but  the  true  nucleoproteids  yield  nuclein  (xanthin) 
bases  while  the  para-nucleoproteids  do  not.  The  nucleoproteids  are  found 
in  the  nucleus  and  protoplasm  of  every  cell.  The  para-nucleoproteids  are 
found  in  milk,  as  caseinogen,  and  in  the  yolk  of  egg,  as  vitellin.  Glyco- 
proteids.  Glycoproteid  is  a  combination  of  a  proteid  substance  with  a  carbo- 
hydrate radicle.  Examples  are  mucin,  which  is  found  in  mucous  secre- 
tions;  and  mucoids,  which  are  found  in  certain  tissues,  cartilages,  etc. 

Mucin.  Mucin  is  a  compound  of  a  globulin  with  a  carbohydrate 
radicle,  and  is  the  characteristic  component  of  mucus;  it  is  contained  also 
in  fetal  connective  tissue,  in  tendons,  and  in  salivary  glands.  It  can  be  obtained 
from  mucus  by  diluting  with  water,  filtering,  treating  the  insoluble  portion 
with  weak  caustic  alkali,  and  reprecipitating  with  acetic  acid.  The  mucins 
derived  from  different  sources  probably  have  different  compositions. 

Mucin  has  a  ropy  consistency.  It  can  be  coagulated;  is  insoluble  in 
water,  salt-solution,  and  very  dilute  muriatic  acid;  is  soluble  in  alkalies  and 
concentrated  sulphuric  acid.  It  gives  the  proteid  reaction  with  Millon's 
reagent  and  with  nitric  acid.  Neither  mercuric  chloride  nor  tannic  acid 
gives  a  precipitate.  It  does  not  dialvze.  When  treated  with  sulphuric  acid 
and  then  neutralized  with  solid  potassium  hydrate,  it  will  give  both  the  biuret 
test,  denoting  the  presence  of  proteid  matter,  and  also  Fehling's  test,  show- 
ing the  presence  of  a  sugar. 

Nucleins.  The  substance  known  as  nuclein  and  found  in  all  cells 
is  really  a  compound  proteid  and  consists  of  a  series  of  bodies  made  up  of  pro- 
teid and  nucleic  acid  in  varying  proportions;  there  is  almost  no  limit  to  the 
possible  variations.  At  one  end  of  the  series  is  nucleic  acid  (C30H52NgP3O17, 
according  to  Kossel),  a  body  containing  the  maximum  (9  to  11  per  cent) 
of  phosphorus  but  without  any  proteid,  and  found  as  such  only  in  sper- 
matozoa; in  the  middle  are  the  nucleins  proper;  and  at  the  other  end 
are  the  nucleoproteids,  containing  the  minimum  of  phosphorus.  As  phos- 
phorus is  the  characteristic  component  of  nucleic  acid,  its  amount  will  meas- 
ure the  amount  of  the  acid  present  in  any  molecule. 

The  chemical  differences  in  the  action  of  cytoplasm  and  karyoplasm 
toward  solvents  are  due  also  to  the  proportion  of  nucleic  acid  and  proteid 
which  they  contain.  These  differences  are  qualitative  and  not  quantitative. 
All  of  the  nucleoproteids  in  the  cell  body  are  true  ones  in  that  they  yield 
nuclein  bases. 

Caseinogen.  Caseinogen,  the  chief  proteid  of  milk,  yields  para- 
nuclei on  digestion.  It  bears  the  same  relation  to  casein  that  fibrinogen 
does  to  fibrin.  When  acted  on  by  rennin  it  splits  into  two  parts  of  which 
one,  the  smaller,  is  peptone-like  in  character.  The  other,  and  larger  part, 
is  known  as  soluble  casein  and  does  not  solidify  in  the  absence  of  calcium 
salts.  As  calcium  is  always  present  in  milk,  it  there  unites  with  it  and  forms 
insoluble  calcium  casein;    strictly  speaking,  therefore^  the  curd  of  milk  is 


86  THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

the  calcium  compound  of  soluble  casein.  Caseinogen  may  be  prepared 
by  adding  dilute  hydrochloric  acid  to  milk  until  the  mixture  is  distinctly 
acid,  when  a  flo.cculent  precipitate  of  caseinogen  will  be  thrown  down  and 
may  be  separated  by  filtration.  The  fat  which  is  carried  down  with  this 
precipitate  may  be  removed  by  washing  with  alcohol  and  then  with  ether. 

Caseinogen  may  also  be  prepared  by  adding  to  milk  an  excess  of  crys- 
tallized magnesium  sulphate  or  sodium  chloride,  either  of  which  salts  causes 
it  to  separate  out.  Caseinogen  gives  the  biuret  and  Millon's  reactions. 
It  is  soluble  in  distilled  water,  dilute  or  strong  alkalies,  and  sulphuric  acid, 
but  insoluble  in  sodium  chloride  and  0.2  per  cent  of  hydrochloric  acid. 

Vitellin.  Vitellin  is  prepared  from  yolk  of  egg  by  washing  with 
ether  until  all  the  yellow  matter  has  been  removed.  The  residue  is  then 
dissolved  in  10  per  cent  saline  solution,  filtered,  and  poured  into  a  large 
quantity  of  distilled  water.  The  precipitate  which  falls  is  impure  vitellin. 
It  gives  the  same  tests  as  myosin,  but  is  not  precipitated  on  saturation  with 
sodium  chloride;   it  coagulates  at  about  750  C. 

Albuminoids.  The  albuminoids  belong  to  the  simple  tissues  of 
the  body  which  are  derived  from  the  epiblast  and  are  characterized  by  a 
lack  of  any  degree  of  activity,  either  physiological  or  chemical.  They  are 
nitrogenous  bodies  derived  from  proteid  matter  in  the  cells,  and  give  crys- 
talline amido-acids  and  nitrogenous  bases  on  decomposition,  but  differ  from 
true  proteids  in  not  having  their  nitrogen  in  a  form  fit  for  the  physiological 
needs  of  the  body.  In  other  words,  they  are  not  true  nitrogen-supplying 
foods,  though  gelatin  has  a  certain  indirect  value  as  it  protects  the  body 
proteids  from  work  in  many  ways.  The  albuminoids  are  soluble  in  dilute 
acids  or  alkalies;  they  may  be  distinguished  from  albumin  or  globulin  by 
being  insoluble  in  water  or  salt  solution  respectively.  Typical  albuminoids 
are  gelatin,  elastin,  chondrin,  keratin,  etc. 

Gelatin.  Gelatin  is  contained  in  the  form  of  collagen,  its  anhy- 
dride, in  bone,  ossein,  teeth,  fibrous  connective  tissues,  tendons,  ligaments, 
etc.  It  may  be  obtained  by  prolonged  action  of  boiling  water  or  of  dilute 
acetic  acid. 

The  percentage  composition  is  O  25.24  per  cent,  H  6.56  per  cent,  N 
17.81  per  cent,  C  50  per  cent,  SO  25  per  cent.  It  contains  more  nitrogen 
and  less  carbon  and  sulphur  than  proteids.  It  is  amorphous,  and  trans- 
parent when  dried.  It  does  not  dialyze;  it  is  insoluble  in  cold  water,  but 
swells  up  to  about  six  times  its  volume;  it  dissolves  readily  on  the  addition 
of  very  dilute  acids  or  alkalies.  It  is  soluble  in  hot  water,  and  forms  a  jelly 
on  cooling,  even  when  only  1  per  cent  of  gelatin  is  present.  It  is  also  soluble 
in  hot  salt  solution.  Prolonged  boiling  in  dilute  acids  or  in  water  destroys 
the  power  of  forming  a  jelly  on  cooling.  On  decomposition  it  gives  2  per 
cent  of  leucin  and  2.6  per  cent  of  argenin,  but  no  tyrosin,  and  a  large  amount 
of  glycocoll  (amido-acetic  acid  or  glycin),  a  crystalline  substance. 


ELASTIN  87 

A  fairly  strong  solution  of  gelatin,  2  per  cent  to  4  per  cent,  gives  the 
xanthoproteic  test,  but  with  no  previous  precipitate  by  nitric  acid;  the  biuret 
test,  the  Millon's  test,  but  with  no  precipitate.  It  is  precipitated  with  tannic 
acid,  with  alcohol  and  picric  acid.  It  is  not  precipitated  with  acetic  acid, 
hydrochloric  acid,  mercuric  chloride,  nor  with  potassium  ferrocyanide, 
and  acetic  acid. 

Elastin  is  found  in  elastic  connective  tissue,  in  the  ligamenta 
subflava,  ligamentum  nuchae,  etc.  It  is  insoluble  in  all  ordinary  reagents, 
but  swells  up  both  in  cold  and  hot  water.  It  is  slowly  soluble  in  strong 
caustic  soda,  when  heated.  It  is  precipitated  by  tannic  acid  and  does  not 
gelatinize.  It  gives  the  proteid  reactions  with  strong  nitric  acid  and  am- 
monia, and  imperfectly  with  Millon's  reagent.  On  decomposition  it  gives 
4.5  per  cent  of  leucin,  a  small  amount  of  argenin,  and  a  mere  trace  of  tyrosin. 
It  is  prepared  by  boiling  with  water,  then  treating  with  artificial  gastric  and 
pancreatic  juices,  then  boiling  again  in  water,  and  then  extracting  with 
acids,  alcohol,  and  ethers;   the  remainder  is  elastin. 

Chondrin  is  found  in  the  condition  of  chondrigen  in  cartilage. 
It  is  obtained  from  chondrigen  by  boiling.  It  is  soluble  in  hot  water,  and 
in  solutions  of  neutral  salts,  e.g.,  sulphate  of  sodium,  in  dilute  mineral  acids, 
caustic  potash,  and  soda.  It  is  insoluble  in  cold  water,  alcohol,  and  ether. 
It  is  precipitated  from  its  solutions  by  dilute  mineral  acids  (excess  redis- 
solves  it),  by  alum,  by  lead  acetate,  by  silver  nitrate,  and  by  chlorine  water. 
On  boiling  with  strong  hydrochloric  acid,  it  yields  grape-sugar  and  certain 
nitrogenous  substances.  Prolonged  boiling  in  dilute  acids,  or  in  water, 
destroys  its  power  of  forming  a  jelly  on  cooling. 

Keratin  is  obtained  from  hair,  horns,  finger-nails,  etc.  Its  com- 
position is  very  similar  to  that  of  ordinary  albumin  and  is  approximately 
C  49.5,  H  6.5,  N  16.8,  S  4,  O  23.2;  the  keratins  obtained  from  the  various 
substances  are  distinct  and  differ  slightly  though  closely  related.  Sulphur 
is  the  characteristic  body  found  in  keratin  and  occurs  as  a  sulphur-contain- 
ing radicle.  A  large  amount  of  mercaptan  sulphur  can  usually  be  obtained. 
On  decomposition,  keratin  yields  argenin  2.26  per  cent,  leucin  10  per  cent, 
and  tyrosin  4  per  cent. 

Keratin  is  insoluble  in  water,  salt,  sodium  carbonate,  and  dilute  hydro- 
chloric acid.  It  is  slowly  soluble  when  warmed  in  caustic  potash  or  sul- 
phuric acid.     It  gives  Millon's  and  the  xanthoproteic  reactions. 

Neurokeratin  is  a  form  of  keratin  which  is  found  in  the  white  substance 
of  Schwann  around  the  axis-cylinders  of  nerves.  It  yields  argenin  5  per 
cent,  leucin  10  per  cent,  and  tyrosin  3.5  per  cent. 

Products  of  Proteid  Decomposition.  The  products  of  proteid  de- 
composition under  the  influence  of  oxidizing  and  hydrolyzing  agents  are 
of  the  greatest  significance  in  indicating  the  character  and  composition  of 
the  proteid  molecule.     Cleavage-products  of  widely  varying  degrees  of  com- 


88  THE    CHEMICAL    COMPOSITION     OF    THE    BODY 

plexity  are  obtained.  But,  running  through  the  cleavage  compounds  are 
certain  nuclei  or  constitution  complexes,  which  in  all  probability  are  found 
in  the  proteid  itself,  in  fact  form  the  basic  structure  of  the  molecule.  The 
following  account  is  taken  from  the  excellent  discussion  by  Witthaus  ("  The 
Medical  Student's  Manual  of  Chemistry"): 

"  Active  oxidizing  agents  attack  the  proteid  molecule  profoundly,  yield- 
ing products  which  are  for  the  most  part  far  removed  from  the  original  sub- 
stance, and  which  are  themselves  products  of  decomposition  of  the  '  atomic 
complexes'  above  referred  to;  acids  and  aldehydes  of  the  fatty,  oxalic,  and 
benzoic  series  and  their  nitrils,  including  hydrocyanic  acid,  ketones,  amido- 
acids,  carbon  dioxid,  and  ammonia.  With  HN03  various  nitro  derivatives 
are  obtained,  and  with  CI,  Br,  and  I  halid  derivatives.  By  oxidation  with 
K2Mn208  an  acid,  oxyprotosulfonic,  containing  the  sulfonic  group,  is 
formed,  and  by  continued  oxidation  peroxyprotonic  acid.  In  oxidation  with 
BaMn208  guanidin  is  one  of  the  products. 

"  Fusion  with  caustic  alkalies  also  causes  deep  decomposition,  the  prod- 
ucts being  ammonia,  mercaptan,  fatty  acids,  amido  fatty  acids,  tyrosin, 
indol,  and  skatol. 

"By  boiling  with  dilute  mineral  acids,  or  with  HCl-{-SnCl2,  the  pro- 
teids  are  hydrolyzed  with  formation  of  hydrogen  sulfid,  ethyl  sulfid  and 
ammonia  as  simple  products,  and  amido-acids,  hexon  bases,  pyrrolidin  and 
oxypyrrolidin  carboxylic  acids,  and  melanoidins,  the  last-named  being  also 
products  of  decomposition  of  the  melanins,  substances  to  which  the  hair 
and  other  dark  portions  of  the  body  owe  their  color.  The  amido-acids, 
including  serin,  tyrosin,  and  cystin,  produced  in  this  and  other  hydrolytic 
decompositions  probably  exist  in  the  proteids  as  polypeptids,  formed  by 
the  union  of  several  amido-acid  complexes. 

"  Considering  the  nitrogen  which  is  split  off,  in  more  or  less  complex 
combination,  on  hydrolysis  of  proteids  by  boiling  with  dilute  acids,  it  appears 
to  have  existed  in  the  parent  proteid  in  five  forms  of  combination,  corre- 
sponding to  five  classes  of  decomposition  products:  i,  Easily  separable, 
so-called  amino-nitrogen,  given  off  as  NH3;  2,  Urea-forming  nitrogen,  in  the 
guanidin  remainder  of  argenin;  3,  Basic  nitrogen,  or  diamido-nitrogen, 
contained  in  basic  nitrogen  compounds,  precipitable  by  phosphotungstic 
acid;  4,  Monamido-nitrogen,  in  monamido-acids;  5,  Humus  nitrogen,  in 
humus-like  melanoidins,  dark-colored,  amorphous,  nitrogenous  remainders. 

"  The  quantitative  distribution  of  nitrogen  in  these  five  groups  differs  in 
different  proteids:  1.  Is  entirely  absent  in  protamins;  1  to  2  per  cent  in  gela- 
tin; 5  to  10  per  cent  in  other  animal  proteids;  13  to  20  per  cent  in  vegetable 
proteids.  2,  In  protamins  22  to  44  per  cent;  in  histons  12  to  13  per  cent; 
in  gelatin  8  per  cent;  in  other  proteids  2  to  5  per  cent.  3,  In  protamins 
63  to  88  per  cent;  in  histons  35  to  42  per  cent;  in  other  animal  proteids 
15  to  25  per  cent;    in  vegetable  proteids  5  to  37  per  cent.     4,  The  greater 


PRODUCTS     OF     PROTEID     DECOMPOSITION  89 

part  of  the  nitrogen,  55  to  76  per  cent,  in  proteids  other  than  protamins  is 
in  this  form.     5,  Varies  within  wide  limits. 

"  The  sulfur,  the  amount  of  which  varies  greatly  in  different  proteids, 
is  given  off  on  hydrolysis  as  cystin,  cystei'n,  a-thiolactic  acid,  mercaptans, 
and  ethyl  sulfid. 

"  The  nitrogen-containing  products  of  hydrolysis  of  proteids  may  be 
thus  classified: 

I.  Aliphatic.     A.    Containing  no  sulfur: 

1,  Guanidin  remainder.     H2N.C  :  NHt  (-hornithin=argenin); 

2,  Monobasic  monamido  acids:    glycocoll,  alanin,  amido-valerianic 

acid,  leucin,  serin; 

3,  Dibasic  monamido-acids:  aspartic  and  glutamic; 

4,  Monobasic  diamido-acids:   ornithin,  lysin; 

E.     Containing  nitrogen  and  sulfur:   Cystin,  cyste'fn; 
II.   Carbocyclic:   phenylamidopropionic  acid,  tyrosin; 
III.  Heterocyclic:    A.  Pyrrol   derivatives:    pyrrolidin   and  oxypyrrolidin 
carboxylic  acids; 

B.  Glyoxalin  derivatives  (?):   histidin; 

C.  Indole  derivatives:   indol,  skatol,  tryptophane." 

The  amido-acids,  although  belonging  to  the  different  series,,  are,  accord- 
ing to  Fischer's  views,  supposed  to  be  combined  into  more  and  more  com- 
plex groupings.  In  the  simplest  combinations  two  or  more  molecules  of 
the  same  or  of  different  amido-acids  combine  with  the  elimination  of  water. 
This  is  the  reverse  of  the  hydrolytic  process  and  results  in  Fischer's  peptids. 
Protamin,  the  simplest  of  the  proteids,  yields  a  relatively  simple  series  of 
amido-acids  and  according  to  Taylor's  work,  already  referred  to,  is  evidently 
a  polypeptid  of  comparatively  complex  structure. 

"  All  proteids  except  the  protamins  and  some  of  the  peptones  contain 
sulfur.  One  fraction  of  this,  referred  to  as  'loosely  combined'  sulfur,  is 
given  off  as  hydrogen  sulfid  by  boiling  with  alkaline  solutions.  It  is  this 
fraction  which  causes  the  formation  of  a  brown  or  black  color,  or  even  a 
black  precipitate,  when  a  proteid  is  heated  with  a  solution  of  caustic  alkali 
in  the  presence  of  lead  acetate,  in  the  'sulfur  test'  for  the  proteids.  The 
second  fraction  is  not  separable  in  this  manner,  but  only,  as  a  sulfate,  by 
fusion  with  saltpeter  and  sodium  carbonate,  or,  as  a  sulfid,  by  fusion  with 
caustic  potash.  The  ratio  of  loosely  combined  sulfur  to  total  sulfur  varies 
nctably  in  different  proteids,  from  §  in  serum  to  §  in  hemoglobin.  It  would 
appear  from  this  constant  difference  in  separability  of  different  portions  of 
sulfur  from  proteids  that  the  molecules  of  these  substances  must  contain  at 
least  two  atoms  of  sulfur  in  different  forms  of  combination.  This  conclu- 
sion, is,  however,  invalidated  by  the  fact  that  both  cystin  and  cysteiin  only 
give  off  one-half  of  their  sulfur,  and  that  very  slowly,  by  .boiling  with  alka- 


90  THE    CHEMICAL     COMPOSITION     OF    THE    BODY 

line  solutions,  yet  the  two  atoms  of  sulfur  in  cystin  are  symmetrically  com- 
bined, and  the  molecule  of  cystei'n  contains  but  one  sulfur  atom. 

"Many  proteids,  not  only  the  glycoproteids,  but  also  true  albumins,  as 
egg  albumin,  serum  albumin,  serum  globulin,  the  nucleoproteids,  etc.,  re- 
act with  Molisch's  reagent,  and,  on  hydrolysis,  split  off  a  carbohydrate 
group,  which  is  an  amido-sugar,  usually  glucosamin,  CHO.CHNH2  (CHOH)3- 
CH2OH,  probably  existing  in  the  proteid  as  a  polysaccharid  complex.  Some 
of  the  nucleoproteids  yield  a  pentose  group,  others  laevulinic  acid.  Other 
proteids,  as  casein,  myosin,  and  fibrinogen,  yield  no  carbohydrate. 

"  The  decomposition  of  proteids  by  the  proteolytic  enzymes,  pepsin, 
trypsin,  and  papain,  consists  of  a  series  of  hydrolyses,  and  results  first  in 
the  formation  of  albumoses  and  peptones,  and  later  by  trypsin,  particularly 
of  polypeptids,  amido  acids,  hexon  bases,  tryptophane,  amins,  diamins,  and 
ammonia.     These  changes  occur  in  the  processes  of  digestion." 

The  Pigments,  etc.  A  number  of  pigments  make  their  appear- 
ance in  the  body;  for  example,  bilirubin,  C16H18N;j03,  is  the  common  bile 
pigment.  Its  crystals  are  bluish-red  in  color  and  are  probably  derived  from 
hematin  of  the  blood.  Biliverdin,  C16H18N204,  is  an  oxidation  product 
of  bilirubin. 

Urochrome  and  Urobilin  occur  in  bile  and  in  urine;  the  latter  is  prob- 
ably identical  with  stercobilin,  which  is  found  in  the  feces.  Uroerythrin  is 
one  of  the  coloring  matters  of  the  urine.     It  is  orange  red  and  contains  iron. 

Melanin  is  a  dark  brown  or  black  pigment  which  occurs  especially  in 
epidermal  tissues,  where  it  is  associated  with  keratin.  It  is  found  in  the 
lungs,  bronchial  glands,  hair,  choroid,  skin,  etc.;  also  in  the  urine  and  in 
melanotic  diseases,  e.g.,  sarcoma.  It  is  a  transformation  product  of  pro- 
teids, from  which  it  can  be  derived  by  boiling  proteid  with  sulphuric  acid. 

Lipochromes  are  pigments,  usually  yellow  or  yellowish-red,  which  are 
associated  with  fat,  being  almost  always  present  in  adipose  tissue.  Little  is 
known  about  them,  but  they  are  thought  to  consist  only  of  C,  H,  and  O. 

OILS    AND    FATS. 

The  animal  oils  and  fats  are  for  the  most  part  mixtures  of  tri-palmitin, 
C3H5(O.C16H310)3,  tri-stearin,  C3H5(O.C18H350)3,  and  tri-olein,  C3H5(O.C18- 
N330)3,  in  different  proportions.  They  are  formed  by  the  union  of  three 
molecules  of  fatty  acid  with  one  molecule  of  the  triatomic  alcohol,  glycerin, 
C3H5(OH)3,  and  are  ethereal  salts  or  esters  of  that  alcohol.  Palmitic  acid 
is  C15H31COOH,  stearic  acid  is  C17H35COOH;  oleic  acid  is  C17H33COOH. 
Human  fat  consists  of  a  mixture  of  tri-palmitin,  tri-stearin,  and  tri-olein, 
of  which  the  two  former  contribute  three-quarters  of  the  whole.  Olein  is 
the  only  liquid  constituent.  The  fat  of  milk  (and  butter)  is  tributyrin; 
butyric  acid  is  C4H802. 


CARBOHYDRATES  91 

Fats  are  insoluble  in  water  and  in  cold  alcohol;  soluble  in  hot  alcohol, 
ether,  and  chloroform.  Colorless  and  tasteless;  easily  decomposed  <  r  saponi- 
fied by  alkalies  or  superheated  steam  into  glycerin  and  the  fatty  acids. 

Certain  of  the  monatomic  Fatty  Acids  are  found  in  the  body, 
viz.,  Formic  CH202,  acetic  C2H402,  and  propionic  C3Hs03,  present  in  sweat, 
but  normally  in  no  other  human  secretion.  They  have  been  found  else- 
where in  diseased  conditions.  Butyric  acid,  C4H802,  is  found  in  milk  and 
in  sweat.  Various  others  of  these  acids  have  been  obtained  from  blood, 
muscular  juice,  feces,  and  urine. 

Of  the  diatomic  fatty  acids,  one  acid,  Lactic  acid,  C3H603,  exists  in  a 
free  state  in  muscle-olasma,  and  is  increased  in  quantity  by  muscular  con- 
traction, but  is  never  contained  in  healthy  blood. 

Soaps.  The  fatty  acids  in  combination  with  soda  or  potash, 
or  similar  bases,  form  soaps  which  are  soluble  in  water,  while  the  fats  are 
not  soluble. 

CARBOHYDRATES. 

The  carbohydrates  are  bodies  composed  of  C,  H,  and  O,  as  aldehydes 
and  ketols.  They  are  classified  as  monosaccharides,  dextrose,  galactose, 
etc.  These  are  the  simplest  molecules  of  the  hexoses.  They  are  sweet, 
odorless,  soluble  in  water,  and  oxidize  readily,  hence  their  reducing  power. 
They  form  crystalline  osazohes.  They  rotate  polarized  light.  Their  for- 
mula is  C6H12O0.  Disaccharides,  maltose,  saccharose,  lactose,  etc.  They 
are  formed  by  the  union  of  two  simpler  molecules  and  the  elimination  of  a 
molecule  of  water.  They  have  the  formula  C12H22On.  And  polysaccharides, 
glycogen,  starch,  dextrin,  gum,  etc.  They  are  much  less  soluble,  can  be 
hydrolyzed  into  the  simpler  forms,  and  have  the  formula  (C6H10O5)u. 

Monosaccharides  are  especially  soluble  and  polysaccharides  are  espe- 
cially insoluble;  monosaccharides  and  disaccharides  do  not  give  colored 
solutions  with  iodine,  while  polysaccharides  do;  monosaccharides  and  (ex- 
cept saccharose)  disaccharides  reduce  Fehling's  solution,  while  polysaccha- 
rides do  not. 

Of  these  the  most  important  are: 

Starch.  It  is  contained  in  nearly  all  plants,  and  in  many  seeds, 
roots,  stems,  and  some  fruits.  It  is  a  soft  white  powder  composed  of  granules 
having  an  organized  structure,  consisting  of  granulose  (soluble  in  water) 
contained  in  a  coat  of  cellulose  (insoluble  in  water);  the  shape  and  size 
of  the  granules  vary  according  to  the  source  whence  the  starch  has  been 
obtained.  It  is  not  crystalline  and  will  not  dialyze.  It  is  insoluble  in  cold 
water,  in  alcohol,  and  in  ether;  it  is  soluble  after  boiling  for  some  time,  and 
may  be  filtered,  in  consequence  of  the  swelling  up  of  the  granulose,  which 
bursts  the  cellulose  coat,  and,  becoming  free,  is  entirely  dissolved  in  water. 
This  solution  is  a  solution  of  soluble  starch  or  amydin.     It  gives  a  blue  color- 


92  THE    CHEMICAL     COMPOSITION     OF    THE    BODY 

ation  with  iodine,  which  disappears  on  heating  and  returns  on  cooling.  It 
is  converted  into  maltose  by  diastase,  and  by  boiling  with  dilute  acids  into 
dextrose. 

Glycogen.  Glycogen  is  a  polysaccharide  contained  in  the  liver, 
and  also  present  in  all  muscles,  but  especially  in  those  of  very  young  animals, 
in  the  placenta,  in  colorless  corpuscles,  and  in  embryonic  tissues.  It  is 
sometimes  called  animal  starch  and  gives  many  reactions  proper  to  starch 
itself.  It  is  freely  soluble  in  water,  and  its  solution  looks  opalescent;  it 
gives  a  port-wine  coloration  with  iodine,  which  disappears  on  heating  and 
returns  on  cooling.  It  is  precipitated  by  basic  lead  acetate  and  is  insoluble 
in  absolute  alcohol  and  in  ether.  It  exists  in  the  liver  during  life,  but  very 
soon  after  death  is  changed  into  sugar.  It  may  be  prepared  by  grinding 
muscle  with  sand  till  a  pasty  mass  is  formed,  boiling  the  mass  in  water  for 
twenty  minutes,  filtering,  and  then  precipitating  the  glycogen  from  the 
filtrate  by  adding  a  little  more  than  an  equal  quantity  of  95  per  cent  alcohol. 
It  is  converted  into  sugar  by  diastase  ferments,  or  into  dextrose  by  boiling 
with  dilute  acids. 

Dextrin.  This  substance  is  made  in  commerce  by  heating  dry 
potato-starch  to  a  temperature  of  4000.  It  is  also  produced  in  the  process 
of  the  conversion  of  starch  into  sugar  by  diastase,  and  by  the  salivary  and 
pancreatic  ferments.  A  yellowish  amorphous  powder,  soluble  in  water, 
but  insoluble  in  absolute  alcohol  and  in  ether.  It  corresponds  almost  ex- 
actly in  tests  with  glycogen ;  but  one  variety  (achroo-dextrin)  does  not  give 
the  port-wine  coloration  with  iodine. 

Cane-Sugar,  or  Saccharose.  It  is  contained  in  the  juices  of  many 
plants  and  fruits,  and  is  extracted  from  the  sugar-cane,  from  beet-root,  or 
from  the  maple.  It  is  crystalline  and  is  precipitated  from  concentrated 
solutions  by  absolute  alcohol.  It  has  no  power  of  reducing  copper  salts 
on  boiling.  It  is  dextro-rotatory.  It  is  not  subject  to  alcoholic  fermenta- 
tion, until  by  inversion  it  is  converted  into  glucose,  it  chars  on  addition  of 
sulphuric  acid,  and  on  heating  with  potassium  or  sodium  hydrate. 

Lactose.  Lactose  is  the  chief  carbohydrate  of  milk.  It  is  less 
soluble  in  water  than  glucose;  it  is  not  sweet,  and  is  gritty  to  the  taste;  but 
it  is  insoluble  in  absolute  alcohol.  In  digestion  it  yields  a  molecule  of  dex- 
trose and  a  molecule  of  galactose.  It  undergoes  alcoholic  fermentation 
with  extreme  difficulty;  gives  the  tests  similar  to  glucose,  but  less  readily. 
It  is  dextro-rotatory  -\-  59°. 

Maltose.  This  sugar  is  produced  by  the  action  of  the  saliva  and 
pancreatic  juice  on  starch.  It  is  also  formed  by  the  action  of  malt  upon 
starch  by  the  action  of  the  ferment  diastase.  It  is  converted  into  dextrose 
by  dilute  sulphuric  acid.  It  is  dextro-rotatory;  ferments  with  yeast;  reduces 
copper  salts;  and  crystallizes  in  fine  needles. 

Dextrose,    or   Glucose.     Dextrose    occurs    widely    diffused   in   the 


INORGANIC    PRINCIPLES  93 

vegetable  kingdom,  in  diabetic  urine,  in  the  blood,  etc.  It  is  usually  ob- 
tained from  grape-juice,  honey,  beet-root,  or  carrots.  As  prepared,  it  really 
is  a  mixture  of  two  isomeric  bodies,  Dextrose  or  grape-sugar,  which  turns 
a  ray  of  polarized  light  to  the  right  (-f-  560),  and  Lcevitlose  or  fruit-sugar, 
which  turns  the  ray  to  the  left. 

It  is  easily  soluble  in  water  and  in  alcohol;  not  so  sweet  as  cane-sugar; 
the  relation  of  its  sweetness  to  that  of  cane-sugar  is  as  3  to  5.  It  is  not  so 
easily  charred  by  strong  sulphuric  acid  as  cane-sugar.  It  is  not  entirely 
soluble  in  alcohol.     It  undergoes  alcoholic  fermentation  with  yeast. 

Dextrose  is  the  characteristic  carbohydrate  of  the  blood.  It  has  the 
power  of  reducing  the  salts  of  silver,  bismuth,  mercury,  and  copper,  either 
to  the  form  of  the  metal  in  the  first  three  cases,  or  to  the  form  of  the  sub- 
oxide in  the  case  with  cuprous  salts.  Upon  this  property  the  chief  tests  for 
the  sugar,  e.g.,  Trommer's  and  Bottcher's,  depend.  It  undergoes  alcoholic 
fermentation  with  yeast,  and  lactic-acid  fermentation  with  bacteria  lactis. 
It  forms  caramel  when  strongly  heated,  and  is  also  charred  with  strong  acids. 

Levulose  is  one  of  the  products  of  the  decomposition  of  cane-sugar  by 
means  of  dilute  mineral  acids,  or  by  means  of  the  ferment  invertin  in  the 
alimentary  canal.  It  reacts  to  the  same  test  as  glucose,  but  is  non-crystal- 
lizable,  and  is  laevo-rotatory.  It  is  soluble  in  water  and  in  alcohol.  Its  com- 
pound with  lime  is  solid,  whereas  that  with  dextrose  is  not. 

Galactose.  This  monosaccharid  is  formed  from  lactose  by  the 
action  of  dilute  mineral  acids,  or  inverting  ferments;  it  may  also  be  ob- 
tained from  cerebrin.  It  undergoes  alcoholic  fermentation,  and  reduces 
copper  salts  to  the  suboxide. 

Inosite.  Inosite  occurs  in  the  heart  and  voluntary  muscles,  as 
well  as  in  beans  and  other  plants.  It  crystallizes  in  the  form  of  large  color- 
less monoclinic  tables,  which  are  soluble  in  water,  but  insoluble  in  alcohol 
or  ether.  It  has  the  formula  of  glucose,  but  is  not  a  sugar.  Inosite  may 
be  detected  by  evaporating  the  solution  containing  it  nearly  to  dryness,  and 
by  then  adding  a  small  drop  of  solution  of  mercuric  nitrate,  and  afterward 
evaporating  carefully  to  dryness,  a  yellowish-white  residue  is  obtained; 
on  further  cautiously  heating,  the  yellow  changes  to  a  deep  rose-color,  which 
disappears  on  cooling,  but  reappears  on  heating.  If  the  inosite  be  almost 
pure,  its  solution  may  be  evaporated  nearly  to  dryness.  After  the  addition 
of  nitric  acid,  the  residue  mixed  with  a  Kttle  ammonia  and  calcium  chloride, 
and  again  evaporated,  yields  a  rose-red  coloration. 

INORGANIC    PRINCIPLES. 

Salts.  The  inorganic  principles  of  the  human  body  are  numerous. 
They  are  derived,  for  the  most  part,  directly  from  food  and  drink,  and  pass 
through  the  system  unaltered.     But  some  salts  are  decomposed  on  their 


94  THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

way,  as  chloride  of  sodium,  of  which  only  four-fifths  of  the  quantity  ingested 
are  excreted  in  the  same  form.  Some  are  newly  formed  within  the  body — 
as,  for  example,  a  part  of  the  sulphates  and  carbonates. 

Much  of  the  inorganic  saline  matter  found  in  the  body  is  a  necessary 
constituent  cf  its  structure,  as  necessary  in  its  way  as  albumin  or  any  other 
organic  principle.  Another  part  is  important  in  regulating  or  modifying 
various  physical  processes,  as  absorption,  solution,  and  the  like.  A  part 
must  be  reckoned  only  as  matter  which  is,  so  to  speak,  accidentally  present, 
whether  derived  from  the  food  or  the  tissues,  and  which  will,  at  the  first 
opportunity,  be  excreted  from  the  body.  The  principal  salts  present  in 
the  body  are: 

Sodium  and  Potassium  Chlorides.  These  salts  are  present  in  nearly 
all  parts  of  the  body.  The  former  seems  to  be  especially  necessary,  judging 
from  the  instinctive  craving  for  it  on  the  part  of  animals  in  whose  food  it  is 
deficient,  and  from  the  diseased  condition  which  is  consequent  on  its  with- 
drawal. The  quantity  of  sodium  chloride  in  the  blood  is  greater  than  that 
of  all  its  other  saline  ingredients  taken  together,  but  it  is  present  chiefly  in 
the  fluids  of  the  body.  In  the  tissues,  the  muscles  for  example,  the  quantity 
of  sodium  chloride  is  less  than  that  of  the  chloride  of  potassium,  which 
forms  a  constant  ingredient  of  protoplasm. 

Calcium  Fluoride.  It  is  present  in  minute  amount  in  the  bones  and 
teeth,  and  traces  have  been  found  in  the  blood  and  some  other  fluids. 

Calcium,  Potassium,  Sodium,  and  Magnesium  Phosphates.  These  phos- 
phates are  found  in  nearly  every  tissue  and  fluid.  In  some  tissues — the  bones 
and  teeth — the  phosphate  of  calcium  exists  in  very  large  amount.  The  phos- 
phate of  calcium  is  intimately  incorporated  with  the  organic  basis  or  matrix, 
but  it  can  be  removed  by  acids  without  destroying  the  general  shape  of  the 
bone.  After  the  removal  of  its  inorganic  salts,  a  bone  is  left  soft,  tough, 
and  flexible. 

Potassium  and  sodium  phosphates,  with  the  carbonates,  maintain  the 
alkalinity  of  the  blood. 

Calcium  Carbonate.  It  occurs  in  bones  and  teeth,  but  in  much  smaller 
quantity  than  the  phosphate.  It  is  found  also  in  some  other  parts.  The 
small  concretions  of  the  internal  ear  (otoliths)  are  composed  of  crystalline 
calcium  carbonate,  and  form  the  only  example  of  inorganic  crystalline  matter 
existing  as  such  in  the  body. 

Potassium  and  Sodium  Carbonates  and  Sulphates.  These  are  found  in 
the  blood  and  most  of  the  secretions  and  tissues. 

Silicon.  A  very  minute  quantity  of  silica  exists  in  the  urine  and  in  the 
blood.     Traces  of  it  have  been  found  also  in  bones,  hair,  and  some  other  parts. 

Iron.  The  especial  place  of  iron  is  in  hemoglobin,  the  coloring-matter 
of  the  blood,  of  which  a  full  account  will  be  given  with  the  chemistry  of  the 
blood.     Iron  is  found,  in  very  small  quantities,  in  the  ashes  of  bones,  mus- 


LABORATORY  EXPERIMENTS  95 

cles,  and  many  tissues,  and  in  lymph  and  chyle,  albumin  of  serum,  fibrin, 
bile,  milk,  and  other  fluids.  A  salt  of  iron,  probably  a  phosphate,  exists  in 
the  hair,  black  pigment,  and  other  deeply  colored  epithelial  or  horny  substances. 
Water.  Water  forms  a  large  proportion,  more  than  two-thirds, 
of  the  weight  of  the  whole  body.  Its  relative  amount  in  some  of  the  principal 
solids  and  fluids  of  the  body  is  shown  in  the  following  table  (from  Robin 
and  Verdeil) : 

Quantity  of  Water  in  Per  Cent. 

Teeth io.o  Bile 88.0 

Bones 13.0  Milk 88.7 

Cartilage 55 .0  Pancreatic  juice 90.0 

Muscles 75  -  o  Urine 93-6 

Ligament 76.8  Lymph 96.0 

Brain 78.9  Gastric  juice 97.5 

Blood 79.5  Perspiration 98.6 

Synovia 80 . 5  Saliva 99 . 5 

In  all  the  fluids  and  tissues  of  the  body — blood,  lymph,  muscle,  gland, 
etc. — water  acts  the  part  of  a  general  solvent,  and  by  its  means  alone  circula- 
tion of  nutrient  matter  is  possible.  It  is  the  medium  also  in  which  all  fluid 
and  solid  aliments  are  dissolved  before  absorption,  as  well  as  the  means  by 
which  all,  except  gaseous,  excretory  products  are  removed.  All  the  various 
processes  of  secretion,  transudation,  and  nutrition  depend  of  necessity  on 
its  presence  for  their  performance. 

The  greater  part,  by  far,  of  the  water  present  in  the  body  is  taken  into 
it  as  such  from  without,  in  the  food  and  drink.  A  small  amount,  however, 
is  the  result  of  the  chemical  union  of  hydrogen  with  oxygen  in  the  oxida- 
tions of  the  body. 

The  loss  of  water  from  the  body  is  intimately  connected  with  excretion 
from  the  lungs,  skin,  and  kidneys,  and,  to  a  less  extent,  from  the  alimentary 
canal.  The  loss  from  these  various  organs  may  be  thus  apportioned  (quoted 
by  Dalton  from  various  observers): 

From  the  Alimentary  canal  (feces) 4  per  cent 

"        Lungs 20        " 

"        Skin  (perspiration) 30        " 

"       Kidneys  (urine) 46        " 

100 

LABORATORY    EXPERIMENTS   ON   THE    CHEMISTRY    OF   THE 

BODY. 

Proteid  General  Reactions.  Certain  tests  depending  on  the  pres- 
ence of  one  or  more  of  the  constituent  groups  in  the  proteid  molecule, 
while  not  conclusive  each  in  itself,  when  taken  together  serve  for  proteid 


96  THE    CHEMICAL    COMPOSITION    OF    THE    BODY 

identification.     Dilute  some  white  of  egg  with  ten  volumes  of  water,  filter 
off  the  precipitated  globulin,  and  use  the  egg  albumin  in  the  following  tests: 

i.  Color  Reactions  of  Proteids.  a.  Xanthoproteic.  Add  concentrated 
nitric  acid  to  2  c.c.  of  the  egg  albumin  in  a  test  tube,  a  lemon-yellow  color 
appears  on  gently  heating.  Add  excess  of  ammonia,  the  color  deepens  to 
orange,  or  with  potassium  hydrate  to  reddish  brown.  Egg  albumin  is  also 
precipitated  by  the  acid,  but  peptone  gives  only  the  color  change.  This  re- 
action depends  upon  the  presence  of  the  tyrosin  nucleus,  or  that  of  indol, 
in  the  proteid  molecule. 

b.  Milton's  reaction.  Millon's  reagent  (mercuric  and  mercurous  nitrate 
in  weak  nitric-acid  solution)  added  to  albumin  solution  gives  a  white  co- 
agulum  in  the  cold  which  turns  purple-red  on  heating  to  700  C.  or  more. 
The  reaction  is  due  to  the  tyrosin  grouping. 

c.  The  biuret  reaction.  Excess  of  sodium  or  potassium  hydrate  with  a  few 
drops  of  2  per  cent  copper  sulphate  in  albumin  solution  when  heated  gives  a 
violet  color.  Albumoses  give  a  pinkish  violet,  and  peptones  a  pink  color  in 
this  reaction,  but  care  must  be  taken  not  to  use  an  excess  of  copper  sulphate. 
The  reaction  seems  to  depend  on  the  presence  of  the  polypeptid  groups. 

d.  Adamkiewicz  reaction.  If  dilute  glyoxylic  acid  be  added  to  proteid 
solution,  and  concentrated  sulphuric  acid  run  under  the  mixture,  a  ring  of 
colors  is  produced  at  the  junction  of  the  layers  when  gentle  heat  is  applied; 
red  at  the  bottom,  then  green  and  violet.  When  shaken  the  whole  becomes 
violet.     The  reaction  depends  upon  the  tryptophane  group. 

2.  Precipitations,  a.  Acid  precipitation.  Proteids  form  insoluble  salts 
with  tannic  acid,  phospho-tungstic  acid,  hydrojerrocyanic  acid,  picric  acid, 
etc.  The  proteid  is  changed  in  the  reaction  and  cannot  be  recovered  by 
breaking  up  the  salt.  Strong  mineral  acids,  hydrochloric  acid,  nitric  acid, 
etc.,  precipitate  proteids,  but  the  peptones  are  soluble  in  excess. 

b.  Heavy  metal  precipitation.  Proteids  form  insoluble  compounds  with 
mercuric  chloride,  lead  acetate,  copper  sulphate,  silver  nitrate,  etc. 

c.  Alcohol.  Proteids  are  precipitated  and  coagulated  by  an  excess  of 
alcohol.     Peptone  alone  is  recoverable  from  alcoholic  precipitation. 

d.  Heat  coagulations.  Make  the  egg-albumin  very  faintly  acid  with 
2  per  cent  acetic  and  heat  to  boiling,  a  white  cloudy  coagulum  appears. 
Albumoses  and  peptones  are  not  heat-coagulated. 

e.  Precipitation  by  neutral  salts.  Add  crystals  of  ammonium  sulphate 
to  egg  albumin  solution  to  saturation,  a  white  flocculent  precipitate  forms. 
The  precipitate  can  be  recovered  as  unchanged  albumin  by  removing  the 
excess  of  salt  by  dialysis. 

Reactions  Characteristic  of  Individual  Proteids.  The  proteid 
groups  most  often  met  by  the  student  are  the  albumins,  globulins,  albumi- 
nates, albumoses,  peptones,  enzyme-coagulated  proteid,  and  heat-coagulated 
proteid.     Each  has  certain  characteristics. 


REACTIONS    CHARACTERISTIC     OF    INDIVIDUAL     PROTEIDS  97 

3.  Albumins,  a.  Solubility  in  water  and  in  neutral  salts.  Test 
each  statement.  Albumin  is  soluble  in  distilled  water,  dialyze  out  the  traces 
of  salts.  It  is  soluble  in  saturated  sodium  chloride  and  saturated  magnesium 
sulphate.     It  is  insoluble  in  saturated  ammonium  sulphate. 

b.  Heat  coagulation.  Mount  a  test  tube  containing  5  c.c.  faintly  acid 
egg-albumin  in  a  500  c.c.  beaker  of  water  which  is  supported  by  a  gauze  and 
ring  stand.  Suspend  a  thermometer  bulb  in  the  middle  of  the  albumin 
solution.  Gradually  heat  the  beaker  of  water,  stirring  constantly,  thus  uni- 
formly heating  the  albumin.  Coagulation  takes  place  at  from  730  to  750  C, 
but  turbidity  a  little  earlier. 

4.  Globulins.  (7.  Solubility  in  water  and  in  neutral  salts.  Test 
the  following  statements,  using  serum  globulin.  Globulin  is  insoluble  in 
distilled  water.  It  is  soluble  in  dilute  neutral  salt  solutions — sodium  chlo- 
ride, magnesium  sulphate,  ammonium  sulphate.  Globulin  is  precipitated 
by  adding  sodium  chloride  or  magnesium  sulphate  to  complete  saturation. 
Fibrinogen  is  precipitated  by  half-saturated  magnesium  sulphate.  Globulins 
are  precipitated  by  adding  to  their  solution  an  equal  volume  of  saturated 
ammonium  sulphate,  i.e.,  by  half-saturated  solution. 

b.  Heat  coagulation.  Test  the  temperature  at  which  globulins  are  heat 
coagulated  by  the  method  described  above,  on  a  sample  of  salted  plasma 
for  fibrinogen  which  coagulates  at  560  C,  and  on  serum  globulin  which 
coagulates  at  730  C. 

5.  Albuminates.  Digest  egg  albumin  in  0.2  per  cent  hydrochloric 
acid  for  an  hour  and  test: 

a.  Solubility.  It  is  insoluble  in  neutral  solutions  and  in  saturated  neu- 
tral salts,  but  soluble  in  dilute  acids  and  alkalies. 

b.  Heat  coagulation.     It  is  not  coagulated  by  heat. 

6.  Albumoses  and  Peptones.  These  proteids  are  formed  in 
the  alimentary  canal  in  the  process  of  digestion  under  the  influence  of  the 
enzvmes,  pepsin  and  trypsin.  Make  a  5  per  cent  solution  of  Armour's  pep- 
tone (which  contains  chiefly  albumoses)  and  test: 

a.  Heat  coagulation.     These  proteids  are  not  coagulated. 

b.  Alcohol.  When  added  to  excess,  a  precipitate  occurs,  but  when 
collected  on  a  filter  the  precipitate  may  be  redissolved  in  water. 

t\  General  proteid  reactions.  These  proteids  fail  to  give  many  of  the 
precipitations,  but  give  the  color  changes.  The  biuret  test  yields  a  rose 
pink  color. 

d.  Xcutral  salts.  Albumoses  are  insoluble  in  saturated  ammonium 
sulphate.  Filter  and  test  the  filtrate  for  proteid.  It  gives  the  biuret  test. 
This  is  due  to  peptones  which  are  soluble  in  all  salt  solutions. 

7.  Ferment  and  Heat-Coagulated  Proteids.  Boiled  egg  white 
should  be  used  for  the  example  of  the  former,  and  fibrin  for  the  latter.  Test 
for  the  color  reactions,  experiment   1,  which  they  both  give.     These  pro- 


98  THE    CHEMICAL    COMPOSITION     OF    THE     BODY 

teids  are  insoluble  in  the  usual  solvents,  though  fibrin  is  slightly  soluble  in 
10  per  cent  sodium  chloride. 

Carbohydrate  Reactions.  The  carbohydrate  representatives  that 
should  be  examined  are: 

8.  Starch.  Make  a  solution  of  starch  by  boiling  i  gram  of 
starch  in  ioo  c.c.  of  distilled  water  and  test. 

a.  Iodine  test.  Shake  up  three  or  four  drops  of  dilute  iodine  solution 
with  2  c.c.  starch.  A  deep  blue  color  appears.  The  color  is  discharged  in 
dilute  alkali  and  reappears  on  acidifying  again.      Heat  also  discharges  the  color. 

b.  Fehling's  test.  Commercial  starch  often  contains  reducing  sugar. 
Boil  2  c.c.  of  starch  solution  with  i  c.c.  of  fresh  Fehling.  If  a  reddish-yellow 
precipitate  settles  on  standing,  the  starch  contains  reducing  sugar  as  an 
impurity.     Starch  does  not  reduce  copper  in  the  presence  of  an  alkali. 

c.  Hydrolysis  of  starch.  Boil  starch  solution  with  5  per  cent  sulphuric 
acid  for  fifteen  minutes.  Test  with  Fehling's  solution,  first  neutralizing  the 
excess  of  acid.  A  copious  precipitate  of  cuprous  oxide  shows  that  the  starch 
has  been  converted  to  reducing  sugar. 

9.  Dextrin.  Make  a  5  per  cent  solution  of  dextrin  in  distilled 
water  and  test: 

a.  Iodine.     This  gives  a  rich  reddish-brown  color  which  is  characteristic. 

b.  Fehling.     Not  reduced  by  dextrin. 

10.  Dextrose.     Test  a  5  per  cent  solution  of  dextrose: 

a.  Iodine  test.     No  reaction. 

b.  Trommer's  test.  Add  caustic  soda  in  excess  and  a  few  drops  of  2  per 
cent  copper  sulphate  and  boil,  or  use  Fehling's  solution.  A  reduction  of  the 
copper  takes  place.  Barfoid's  solution  also  is  reduced  by  dextrose,  but  not 
by  maltose. 

11.  Glycogen.  Make  up  10  c.c.  of  a  1  per  cent  solution  of  gly- 
cogen and  repeat  the  tests: 

a.  Iodine.  This  gives  a  wine-red  color  very  much  like  that  given  by 
dextrin.     The  color  is  discharged  by  heating,  but  reappears  on  cooling. 

b.  Lead  acetate.  It  gives  a  precipitate,  but  one  must  guard  against 
the  presence  of  proteid  as  an  impurity. 

c.  Tromtner's  test.     Glycogen  does  not  reduce  copper. 

The  Fats.  The  common  fats  are  the  oleins,  palmitins,  and 
stearins.  These  are  glycerin  salts  of  the  fatty  acids.  The  animal  fats  are 
mixtures  of  these  fats  in  different  proportions. 

12.  Neutral  Fat.  a.  Melting-point.  Compare  neutral  olive  oil, 
some  fresh  rendered  lard,  and  some  tallow.  The  former  is  fluid  at  ordinary 
room  temperature.  Determine  the  melting-points  of  the  lard  and  of  the 
tallow  by  the  method  of  Wiley.  Fill  a  test  tube,  one-half  full  of  water  and 
add  a  two-inch  top  layer  of  alcohol.  Prepare  a  thin  flake  of  fat  and  suspend 
it  in  the  test  tube  at  the  dividing  line  of  the  water  and  alcohol.     Insert  the 


FAT    ACIDS  99 

bulb  of  a  thermometer  at  the  same  level.  Mount  the  test  tube  with  the 
thermometer  in  a  beaker  on  a  ring  stand,  fill  the  beaker  with  water  above  the 
level  of  the  content  of  the  test  tube,  and  gradually  heat  with  stirring  of  the 
water  in  the  beaker.  At  the  melting  temperature  the  flake  of  fat  will  run 
into  a  round  drop. 

b.  Solubility.  Fat  is  insoluble  in  water,  but  soluble  in  ether,  chloro- 
form, benzol,  and  in  alcohol. 

c.  Saponification.  Heat  some  fat  in  an  evaporating-dish,  add  sodium 
hydrate,  and  boil.  Saponification  takes  place.  The  soap  is  soluble  in  water. 
Add  25  per  cent  sulphuric  acid  to  some  of  the  soap,  the  fatty  acid  is  liber- 
ated and  collects  on  the  surface  of  the  solution. 

13.  Fat  Acids.  Collect  some  of  the  fatty  acids,  wash  to  remove 
excess  of  alkali,  and  dissolve  in  ether. 

a.  Acid  reaction.  Add  ether  solution  of  the  fatty  acid  to  neutral  litmus, 
or  to  faintly  alkaline  phenolphthalein.  The  former  turns  red,  and  the  red  of 
the  latter  is  discharged,  the  acid  reaction. 

b.  Acrolein  test.  Evaporate  the  ether  from  2  c.c.  of  the  solution,  add 
potassium  bisulphate  crystals  to  the  acid  in  a  test  tube,  and  raise  to  a  high 
heat  over  a  bunsen.  No  acrolein  is  given  off.  Repeat  on  neutral  fat  and 
on  glycerin.     Both  liberate  the  irritating  fumes  of  acrolein. 

14.  Emulsification.  0.  Shake  up  neutral  olive  oil  and  water,  no 
emulsion  is  formed  and  the -oil  quickly  separates. 

b.  Add  a  couple  of  drops  of  fatty  acid,  a  very  good  but  temporary  emul- 
sion is  now  formed. 

c.  Use  rancid  fat,  a  temporary  emulsion  is  formed. 

d.  Add  a  little  soap  to  either  of  the  above,  i.e.,  c.  A  good  permanent 
emulsion  is  now  formed. 

15.  The  Salts.  A  goodly  series  of  salts  is  present  in  the  body, 
the  most  important  elements  of  which  are  sodium,  potassium,  calcium,  mag- 
nesium, and  iron,  as  chlorides,  sulphates,  and  phosphates.  Burn  50  c.c.  cf 
blood  at  a  dull  red  heat,  take  up  in  water  and  test: 

a.  Chlorides.  Add  1  per  cent  nitrate  of  silver,  a  white  precipitate,  in- 
soluble in  nitric  acid,  soluble  in  ammonia,  and  reprecipitated  by  nitric  acid. 

b.  Sulphates.  Add  barium  chloride,  a  white  precipitate,  which  quickly 
settles  and  is  insoluble  in  nitric  acid. 

c.  Phosphates.  Add  nitric  acid  and  a  few  drops  of  1  per  cent  ammonium 
molybdate,  a  yellow  granular  precipitate  of  phosphorus.  It  is  soluble  in 
ammonia,  reprecipitated  in  nitric  acid. 

d.  Calcium.  Make  a  hydrochloric  acid  extract  of  the  ash  of  blood 
above,  add  ammonia  to  excess,  then  a  solution  of  ammonium  oxalate,  a  deli- 
cate white  precipitate  where  traces  are  present. 

e.  Iron.  Add  hydrochloric  acid  and  a  few  drops  of  ferrocyanide  of  po- 
tassium.    A  blue  color  indicates  the  presence  of  iron. 


PLATE    II 

VARIETIES   OF   LEUCOCYTES 

a.  Polymor phonnclear  Neutrophiles.  Note  the  varieties  in  size  and  shape  of  gran- 
ules, the  regular  staining  of  the  nuclei,  the  light  space  around  them,  their  relatively  central 
position  in  the  cell. 

b.  Myelocytes.  Note  the  identity  of  granules  with  those  just  described;  the  even,  pale 
stain  of  nuclei,  their  position  near  the  surface  (edge)  of  the  cell.  The  two  cells  figured 
indicate  the  usual  variations  in  size  of  the  whole  cell. 

c.  Small  Lymphocytes.  In  the  cell  at  the  left  note  the  transparent  protoplasm;  in  the 
cell  next  to  it  note  the  very  pale  pink  of  protoplasm  around  the  nucleus  which  is  deeply 
stained,  especially  at  the  periphery.  The  next  cell  has  an  indented  nucleus;  its  protoplasm 
relatively  distinct.  The  cell  on  the  extreme  right  shows  no  protoplasm  and  is  probably 
necrotic.  In  all  note  absence  of  granules  with  this  stain.  With  basic  stains  a  blue  net- 
work appears  in  the  protoplasm. 

d .  Large  Lymphocytes.  Note  the  pale  stain  of  nuclei  and  protoplasm,  regularity  of 
outline;  indented  nucleus  in  one.  Every  intermediate  stage  between  these  and  the 
"small "  lymphocytes  occurs,  and  the  distinction  between  them  is  arbitrary. 

e.  Eosinophile.  Note  regular  shape,  loose  connection  of  granules,  their  copper  color, 
their  uniform  and  relatively  large  size,  and  spherical  shape. 

/.  Eosinophilic  Myelocyte.  Note  similarity  to  the  ordinary  myelocytes  b,  except  as 
regards  granules.     Color  of  granules  may  be,  as  in  e,  ordinary  eosinophile. 

All  the  above  were  stained  with  the  Ehrlich  triacid  stain,  and  drawn  with  camera 
lucida.     Oil  immersion  objective  ^  and  ocular  No.  hi.  of  Leitz.     (Cabot.,) 


KIRKES'   PHYSIOLOGY 


PLATE  H. 


Polymorphonuclear 
neutrophiles    — 


;*  j.^J-Myelocytes 
Small  Lymphocytes 


.Large  Lymphocytes 


*v»  «  *  .  • 


Eosinophile  ---^te^wf? 


»•. 


Eosinophilic 
Myelocyte 


Varieties  of  Leucocytes. 


R.  C.  fVhot  fee. 


Lith.  A.n«t.  v.  E.  A.  Fnnkt.  Leipiifc. 


CHAPTER    IV 

THE    BLOOD 

The  blood  is  the  fluid  medium  of  which  all  the  tissues  of  the  body  are 
nourished.  By  means  of  the  blood  materials  absorbed  from  the  alimentary 
canal  as  well  as  oxygen  taken  from  the  air  in  the  lungs  are  carried  to  the  tissues, 
while  substances  which  result  from  the  metabolism  of  the  tissues  are  carried 
to  the  excretory  organs  to  be  removed  from  the  body.  The  blood  also  acts 
as  a  medium  of  exchange  for  products  of  glandular  activity  between  the  various 
tissues  themselves,  internal  secretions,  and  it  is  a  factor  in  the  regulation 
of  body  temperature.  The  blood  is  a  somewhat  viscid  fluid,  and  in  man 
and  in  all  other  vertebrate  animals,  with  the  exception  of  two  of  the  lowest, 
is  red  in  color.  The  exact  color  of  the  blood  is  variable;  that  taken  from 
the  systemic  arteries,  from  the  left  side  of  the  heart  and  from  the  pulmonary 
veins  is  of  a  bright  scarlet  hue;  that  obtained  from  the  systemic  veins,  from 
the  right  side  of  the  heart,  and  from  the  pulmonary  artery  is  of  a  much 
darker  color,  which  varies  from  bluish-red  to  reddish-black.  At  first 
sight  the  red  color  appears  to  belong  to  the  whole  mass  of  blood,  but  on 
further  examination  this  is  found  not  to  be  the  case.  In  reality  blood  con- 
sists of  an  almost  colorless  fluid,  called  plasma  or  liquor  sanguinis,  in  which 
are  suspended  numerous  minute  masses  of  protoplasm,  called  blood-corpus- 
cles. The  corpuscles  are  of  the  two  varieties,  the  white  ameboid  corpuscles, 
or  leucocytes,  and  the  red  corpuscles,  erythrocytes.  The  latter  compose 
by  far  the  larger  mass  of  blood-cells  and  contain  the  red  pigment,  hemoglobin, 
to  which  the  color  of  the  blood  is  due. 

The  plasma  or  fluid  part  of  the  blood  is  a  remarkably  complex  chemical 
mixture.  It  is  kept  in  constant  rapid  circulation  through  the  blood-vessels 
of  the  body  and  is,  therefore,  thoroughly  mixed  and  homogeneous  in  character. 

Quantity  of  the  Blood.  The  quantity  of  blood  in  any  animal 
under  normal  conditions  bears  a  fairly  constant  relation  to  the  body  weight. 
The  amount  of  blood  in  man  averages  j%  to  T3T  °f  the  body  weight.  In 
other  mammals  the  proportion  of  blood  is  also  fairly  constant,  varying  from 
^  to  JL  of  the  body  weight.  In  many  of  the  lower  vertebrates  the  relative 
quantity  of  blood  is  very  much  less. 

An  estimate  of  the  quantity  in  man  which  corresponded  very  nearly 
with  this  proportion  has  been  more  than  once  made  by  methods  illustrated 
by  the  following  data:    A  criminal  was  weighed  before  and  after  decapita- 

101 


102  THE     liLOOI) 

tion;  the  difference  in  the  weight  representing  the  quantity  of  blood  which 
escaped.  The  blood-vessels  of  the  head  and  trunk  were  then  washed  out 
by  the  injection  of  water  until  the  fluid  which  escaped  had  only  a  pale  red 
or  straw  color.  This  fluid  was  then  also  weighed,  and  the  amount  of  blood 
which  it  represented  calculated  by  comparing  the  proportion  of  solid  matter 
contained  in  it  with  that  of  the  first  blood  which  escaped  on  decapitation. 
Two  experiments  of  this  kind  gave  precisely  similar  results  (Weber  and 
Lehmann). 

This  quantity  of  blood  is  distributed  in  the  different  parts  of  the  body, 
chiefly  in  the  muscles,  the  liver,  the  heart,  and  larger  blood-vessels,  as  shown 
by  the  following  figures  determined  on  the  rabbit  by  Ranke  (from  Vierordt): 

Per  cent. 

Spleen .' o .  23 

Brain  and  cord 1 .24 

Kidney 1 .63 

Skin 1 2.10 

Abdominal  viscera 6-3° 

Cartilage 8 .  24 

Heart,  lungs,  and   large  blood-vessels 22 . 76 

Resting  muscle 29 .  20 

Liver 29-3° 

It  should  be  remembered,  in  connection  with  these  estimations,  that 
the  quantity  of  the  blood  must  vary  very  considerably,  even  in  the  same 
animal,  with  the  amount  of  both  the  ingesta  and  egesta  of  the  period  im- 
mediately preceding  the  experiment.  It  has  been  found,  for  example,  that 
the  quantity  of  blood  obtainable  from  the  body  of  a  fasting  animal  rarely 
exceeds  a  half  of  that  which  is  present  soon  after  a  full  meal. 

COAGULATION    OF    THE    BLOOD. 

The  most  characteristic  property  which  the  blood  possesses  is  that  of 
clotting  or  coagulating.  This  phenomenon  may  be  observed  under  the 
most  favorable  conditions  in  blood  which  has  been  drawn  into  an  open  vessel. 
In  about  two  or  three  minutes,  at  the  ordinary  temperature  of  the  air,  the 
surface  of  the  fluid  is  seen  to  become  semi -solid  or  jelly-like,  and  this  change 
takes  place,  in  a  minute  or  two  afterward,  at  the  sides  of  the  vessel  in  which 
it  is  contained  and  then  quickly  extends  throughout  the  entire  mass.  The 
time  which  is  occupied  in  these  changes  is  about  eight  or  nine  minutes.  The 
solid  mass  is  of  exactly  the  same  volume  as  the  previously  liquid  blood,  and 
adheres  so  closely  to  the  sides  of  the  containing  vessel  that  if  the  latter  be 
inverted  none  of  its  contents  escape.  The  solid  mass  is  the  crassamentum 
or  clot.  If  the  clot  be  watched  for  a  few  minutes,  drops  of  a  light,  straw- 
colored  fluid,  the  serum,  may  be  seen  to  make  its  appearance  on  the  surface, 
and,  as  it  becomes  greater  and  greater  in  amount,  to  form  a  complete  super- 


COAGULATION     OF    THE    BLOOD  103 

ficial  stratum  above  the  solid  clot.  At  the  same  time  the  fluid  begins  to 
transude  at  the  sides  and  at  the  under  surface  of  the  clot,  which  in  the  course 
of  an  hour  or  two  floats  in  the  liquid.  The  appearance  of  the  serum  is  due 
to  the  fact  that  the  clot  contracts,  thus  squeezing  the  fluid  out  of  its  mass. 
The  first  drops  of  serum  appear  on  the  surface  about  eleven  or  twelve  minutes 
after  the  blood  has  been  drawn;  and  the  fluid  continues  to  transude  for  from 
thirty-six  to  forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  the  plasma  of  an  in- 
soluble substance  called  fibrin.  This  fibrin  forms  threads  or  strands  through 
the  mass  in  every  direction.  The  strands  adhere  to  each  other  wherever 
they  come  in  contact,  thus  forming  a  very  dense  tangle  and  meshwork  which 
incloses  within  itself  the  blood-corpuscles.  The  clot  when  first  formed, 
therefore,  includes  the  whole  of  the  blood  in  an  apparently  solid  mass,  but 
soon  the  fibrinous  meshwork  begins  to  contract  and  the  serum  is  squeezed 
out.  "When  a  large  part  of  the  serum  has  been  squeezed  out  the  clot  is  found 
to  be  smaller,  but  firmer  and  harder,  as  it  is  now  made  up  largely  of  fibrin 
and  blood-corpuscles.  Thus  in  coagulation  there  is  a  rearrangement  of  the 
constituents  of  the  blood;  liquid  blood  being  made  up  of  plasma  and  blood- 
corpuscles,  and  clotted  blood  of  serum  and  clot. 

Liquid  Blood. 


Plasma.  Corpuscles. 


Serum 


Clot. 


Clotted  Blood. 

The  rapidity  with  which  coagulation  takes  place  varies  greatly  in  different 
animals  and  at  different  times  in  the  same  animal.  Where  coagulation  is 
very  slow  the  red  corpuscles,  which  are  somewhat  heavier  than  plasma, 
often  have  time  to  settle  considerably  before  the  fibrin  is  formed.  If  the 
blood  is  rapidly  cooled  to  something  approaching  o°  C.  then  the  clot  is  very 
greatly  delayed.  Horse's  blood  is  particularly  favorable  for  demonstrating 
this  point.  In  it  clotting  occurs  so  slowly  that  very  often  the  red  corpuscles 
will  completely  settle  out,  and  when  the  blood  is  again  warmed  and  the  clotting 
takes  place  there  is  a  superficial  stratum  differing  in  appearance  from  the 
rest  of  the  clot,  and  is  of  a  grayish-yellow  color.  This  is  known  as  the  bufjy 
coat  or  crusla  phlogistica.  The  buffy  coat,  produced  in  the  manner  just 
described,  commonly  contracts  more  than  the  rest  of  the  clot,  on  account  of 
the  absence  of  colored  corpuscles  from  its  meshes.  When  the  clot  is  allowed 
to  stand  the  white  corpuscles  migrate  to  the  surface  by  ameboid  movement, 


104 


THE    BLOOD 


often  in  such  numbers  that  they  form  a  distinct  superficial  layer,  grayish- 
white  in  appearance. 

That  the  clotting  of  blood  is  due  to  the  gradual  appearance  in  it  of  fibrin 
may  be  easily  demonstrated.  For  example,  if  recently  drawn  blood  be 
whipped  with  a  bundle  of  twigs  or  wires,  the  fibrin  may  be  withdrawn  from 
the  blood  before  it  can  entangle  the  blood-corpuscles  within  its  meshes,  as 
it  adheres  to  the  twigs  in  stringy  threads  relatively  free  from  corpuscles. 
The  blood  from  which  the  fibrin  has  been  withdrawn  no  longer  exhibits  the 
power  of  spontaneous  coagulability  and  it  is  now  called  defibrinated  blood. 
Although  these  facts  have  long  been  known,  the  closely  associated  problem 
as  to  the  exact  manner  in  which  fibrin  is  formed  is  by  no  means  so  simple. 

Fibrin  is  derived  from  the  plasma.  Pure  plasma  may  be  procured  by 
delaying  coagulation  in  blood  by  keeping  it  at  a  temperature  slightly  above 


Fig.  107. — Reticulum  of  Fibrin,  from  a  Drop  of  Human  Blood,  after  Treatment  with  Rosanilin. 

(Ranvier.) 


freezing  point,  until  the  colored  corpuscles  have  subsided  to  the  bottom  of 
the  containing  vessel.  The  blood  of  the  horse  is  specially  suited  for  the  pur- 
poses of  this  experiment.  A  portion  of  the  colorless  supernatant  plasma, 
if  decanted  into  another  vessel  and  exposed  to  the  ordinary  temperature  of 
the  air,  will  coagulate,  producing  a  clot  similar  in  all  respects  to  blood  clot, 
except  that  it  is  colorless  from  the  absence  of  red  corpuscles.  If  some  of 
the  plasma  be  diluted  with  twice  or  three  times  its  bulk  of  normal  saline 
solution  (0.9  per  cent),  coagulation  is  delayed,  and  the  stages  of  the  gradual 
formation  of  fibrin  in  it  may  be  conveniently  w'atched.  The  viscidity  which 
precedes  the  complete  coagulation  may  be  actually  seen  to  be  due  to  the 
formation  of  fibrils  of  fibrin — first  of  all  at  the  edge  of  the  fluid-containing 
vessel,  and  then  gradually  extending  throughout  the  mass.  If  a  portion  of 
plasma,  diluted  or  not,  be  whipped  with  a  bundle  of  twigs  the  fibrin  may 
be  obtained  as  a  solid,  stringy  ma<s,  just  in  the  same  way  as  from  the  entire 


THEORIES     OF     COAGULATION 


105 


blood,  and  the  resulting  fluid  no  longer  retains  its  power  of  spontaneous 
coagulability. 

Theories  of  Coagulation.  It  is  evident  that  the  blood  plasma 
contains  some  substance  or  substances  which  take  part  in  the  formation  of 
fibrin.  By  numerous  investigations  it  has  been  found  that  the  direct  ante- 
cedent of  the  fibrin  is  the  proteid  substance,  fibrinogen.  This  fibrinogen 
exists  in  the  blood  plasma  at  all  times,  but  is  somewhat  increased  under 
certain  conditions.  The  fibrinogen  is  reacted  on  by  another  substance 
known  as  thrombin,  or  by  the  historical  term  fibrin  ferment.  We  shall  not 
present  the  numerous  theories  which  have  been  held  concerning  blood  coagu- 
lation, many  of  which  have  been  more  or  less  disproven,  but  shall  try  to  present 


Blood 


Tissue  Cells 


Plasma 


Blood  Plates         Corpuscles 


Neutral  Salts        Fibrinogen 

(lor  dissolving 

fibrinogen)  /   \ 


Fibrin-globulin 


Calcium  Salts 


Prothrombin 


Thrombokinase 


Thrombin 


F'brin 
Fig.  ioS. — Schema  of  Coagulation. 


the  condensed  statement  of  the  present  explanations  of  this  intricate  phenom- 
enon. One  may  start  from  the  statement  that  the  fibrinogen  of  the  plasma 
when  acted  upon  by  the  thrombin,  also  of  the  plasma,  produces  an  insoluble 
substance,  fibrin.  The  chief  interest  centers  around  the  origin  and  char- 
acter of  the  fibrinogen,  the  origin  and  nature  of  the  thrombin,  and  the  condi- 
tions which  influence  its  activity. 

The  fibrinogen  is  present  in  blood  plasma  of  the  circulating  blood  of  the 
body  at  all  times.  It  can  be  separated  from  plasma  by  various  chemical 
means,  and  when  purified  can  be  made  to  form  fibrin  under  proper  conditions. 
All  observers  are  agreed  that  this  proteid  is  the  immediate  precursor  of  the 
insoluble  fibrin.  Its  origin  in  the  blood  has  been  traced  with  some  degree 
of  certainty  to  the  disintegration  of  the  white  blood-corpuscles. 

The  thrombin  is  the  substance  which  reacts  on  the  fibrinogen  in  the  proc- 
esses of  fibrin  formation.     It  does  not  exist  in    the  living  blood-vessels,  or  at 


100  THE    BLOOD 

least  is  present  only  in  minute  traces,  but  makes  its  appearance  immediately 
the  blood  is  drawn.     Its  origin  is  therefore  of  peculiar  interest. 

It  has  been  claimed  by  some,  notably  Peckelharing,  that  thrombin  is  a 
calcium  compound.  At  any  rate,  it  is  definitely  proven  that  calcium  is  a 
necessary  element  in  the  formation  of  the  clot. 

The  substance  thrombin,  fibrin  ferment,  quickly  appears  in  consider- 
able quantity  when  blood  is  drawn  under  ordinary  conditions.  Its  appearance 
is  due  to  at  least  three  antecedent  substances,  prothrombin  (thrombogen), 
calcium,  and  thrombokinase.  The  sources  of  these  substances  and  the 
part  taken  by  each  in  the  process  of  coagulation  are  as  follows:  If  blood 
be  drawn,  centrifugalized,  and  the  blood  plates  separated,  freed  from  plasma, 
and  suspended  in  water,  their  solution  will  cause  the  formation  of  fibrin 
from  fibrinogen  in  the  presence  of  calcium  and  thrombokinase.  The  blood 
platelets  are,  therefore,  the  source  of  the  thrombogen.  The  thrombokinase 
can  be  traced  to  its  origin  in  the  tissue  cells  and  the  formed  elements  of  the 
blood,  especially  the  leucocytes.  If  blood  is  drawn  from  the  vessels  with 
due  precautions  not  to  allow  it  to  come  in  contact  with  the  cut  vessel,  or  other 
tissue,  clotting  is  very  much  delayed.  The  plasma  if  separated  by  the  cen- 
trifuge will  remain  unclotted  for  a  long  time  as  shown  by  Howell  for  the 
terrapin's  plasma.  This  plasma  will  quickly  clot  at  any  time  if  a  few  drops 
of  tissue  extract  in  salt  solution  be  added.  A  solution  of  extract  of  washed 
white  corpuscles  acts  to  increase  the  rapidity  of  coagulation.  If  precautions 
are  taken  to  draw  the  blood  in  such  a  manner  as  to  remove  the  calcium  from 
the  plasma,  no  clot  is  formed. 

The  calcium  which  exists  in  solution  in  the  plasma  to  the  extent  of  0.026 
per  cent  can  be  removed  by  precipitation  with  oxalate  solution,  or  by  fluorides. 
Oxalate  plasma  contains  both  prothrombin  and  thrombokinase,  and  when- 
ever calcium  chloride  is  added  to  slight  excess  coagulation  takes  place.  In 
fluoride  plasma  one  must  add  both  calcium  and  thrombokinase  as  that  sub- 
stance seems  to  prevent  the  setting  free  of  thrombokinase  from  the  corpuscles. 
The  prothrombin  is  not  interfered  with  by  fluoride. 

In  a  word,  one  may  say  that  the  coagulation  of  the  blood  takes  place 
because  of  the  formation  of  fibrin  from  fibrinogen  by  the  action  of  thrombin. 
The  fibrinogen  is  constantly  present  in  the  plasma.  The  thrombin  is  formed 
by  the  interaction  of  three  substances,  prothrombin,  thrombokinase,  and  cal- 
cium. The  prothrombin  arises  chiefly  from  the  disintegration  of  the  blood 
platelets  when  the  blood  leaves  the  blood-vessels.  The  thrombokinase 
originates  in  tissue  cells  of  the  blood  and  of  the  organs  of  the  body  in  general. 
The  calcium  is  present  in  the  blood  plasma  at  all  times. 

Conditions  Affecting  Coagulation.  From  the  preceding  discussion 
it  is  evident  that  the  rapidity  of  the  coagulation  of  the  blood  will  be  influenced 
by  anything  that  will  influence  the  formation  of  the  fibrin  factors  or  their 
interaction.     The  most  important  influences  are  the  following: — 


MORPHOLOGY    OF    THE    BLOOD  107 

Temperature.  Cold  retards  coagulation.  Gentle  warmth,  400  C,  hastens 
but  a  temperature  above  560  C.  destroys  clotting,  since  that  temperature  heat- 
coagulates  the  fibrinogen. 

Contact  with  Foreign  Bodies.  Such  contact  hastens  clotting.  This  is 
due  to  the  influence  of  such  bodies  on  the  formation  of  fibrin  factors,  es- 
pecially the  substances  that  arise  from  the  disintegration  of  the  leucocytes. 

Condition  of  the  Blood-Vessel  Walls.  Intravascular  clotting  often  takes 
place  upon  injury  of  the  endothelial  lining  of  the  blood-vessel,  probably 
from  the  liberation  of  thrombokinase  in  quantity  too  great  for  elimination 
by  the  healthy  portion  of  the  wall.  The  healthy  endothelium  no  doubt  is 
an  important  factor  in  eliminating  the  small  amounts  of  the  fibrin  factors 
that  must  be  constantly  forming.  The  open  wounds  and  lacerations  of 
tissue  that  accompany  the  loss  of  blood  by  accident  are  the  very  conditions 
most  favorable  to  clotting,  since  large  amounts  of  tissue  extract,  thrombo- 
kinase, are  formed  under  these  conditions. 

Neutral  Salts.  The  addition  of  neutral  salts  in  the  proportion  of  2  or  3 
per  cent  and  upward.  When  added  in  large  proportions,  most  of  these 
saline  substances  prevent  coagulation  altogether.  Coagulation,  however, 
ensues  on  dilution  with  water.  The  time  during  which  salted  blood  can  be 
thus  preserved  in  a  liquid  state,  and  coagulated  by  the  addition  of  water, 
is  quite  indefinite. 

Oxalates  and  Fluorides.  These  and  other  precipitanfs  of  calcium  pre- 
vent clotting  by  removing  this  substance. 

Peptone.  The  injection  of  commercial  peptone  in  the  blood-vessels  of 
an  animal  to  the  extent  of  0.5  gram  of  peptone  per  kilo  weight  of  the  body 
of  the  animal  will  deprive  the  blood  of  the  power  of  coagulation.  If  a  smaller 
quantity  be  injected  the  coagulation  of  the  blood  will  be  delayed.  If  peptone 
blood  is  drawn  and  centrifuged,  the  plasma  obtained,  which  is  called  peptone 
plasma,  can  be  made  to  coagulate  by  diluting  sufficiently  with  water  and 
letting  it  stand  a  long  time.  Peptone  plasma  in  the  blood-vessels  of  the  ani- 
mal gradually  regains  the  power  to  coagulate. 

MORPHOLOGY    OF    THE  BLOOD. 

The  corpuscles  floating  in  the  fluid  plasma  of  the  blood,  when  separated 
by  a  centrifugal  machine  are  found  to  make  up  45  to  50  per  cent  of  the  total 
mass  of  the  blood.  These  corpuscles,  or  formed  elements,  are  of  three 
varieties,  the  red  corpuscles  or  erythrocytes,  the  white  corpuscles  leucocytes, 
and  the  blood  platelets  which  have  been  called  thrombocytes. 

Red  Corpuscles  or  Erythrocytes.  Human  red  blood-corpuscles 
are  circular,  biconcave  discs  with  rounded  edges,  from  7  ;i  to  8  ;i  in  diameter, 
and  about  2  p.  in  thickness.  When  viewed  singly  they  appear  of  a  pale 
yellowish  tinge;    the  deep  red  color  which  they  give  to  the  blood  being  ob- 


108 


Tin:     1ILOOI) 


servable  in  them  only  when  they  are  seen  en  masse.  They  are  composed 
of  a  colorless,  structureless,  and  transparent  filmy  framework  or  stroma, 
infiltrated  in  all  parts  by  the  red  coloring  matter,  the  hemoglobin.  The 
stroma  is  tough  and  elastic,  so  that  as  the  corpuscles  circulate  they  admit 
of  elongation  and  other  changes  of  form  in  adaptation  to  the  vessels,  yet 
recover  their  natural  shape  as  soon  as  they  escape  from  compression. 

Number  and  Character  oj  the  Red  Corpuscles.  The  normal  number  of  red 
blood-cells  in  a  cubic  millimeter  of  human  blood  was  estimated  by  Welcker, 
in  1854,  to  be  5,000,000  in  men  and  4,500,000  in  women.  Numerous  recent 
observations,  however,  have  shown  that  these  estimates  are  a  little  low, 
especially  in  men,  and  the  average  number  has  been  placed  by  different 
authorities  at  various  points  between  5,000,000  and  5,500,000.  Still  the 
original  numbers  as  given  by  Welcker  are  accepted  at  the  present  day  as  being 
sufficiently  accurate  for  ordinary  purposes.  It  has  been  also  shown  that 
there  are  many  distinct  physiological  variations  in  the  number,  depending 


Fig.  109. 


Fi. 


Fig.  109. — Red  Corpuscles  in  Rouleaux.     The  rounded  corpuscles  are  white  or  uncolored. 
Fig.  1 10. — Corpuscles  of  the  Frog.     The  central  mass  consists  of  nucleated  colored  corpuscles. 
The  other  corpuscles  are  two  varieties  of  the  colorless  form. 


on  the  time  of  day,  digestion,  sex,  etc.  The  number  of  red  cells  usually 
diminishes  in  the  course  of  each  day,  while  the  leucocytes  increase  in  number. 
It  has  been  suggested  that  this  is  due  to  the  influence  of  digestion  and  exercise. 
It  has  generally  been  found  that  within  half  an  hour  or  an  hour  after  a 
full  meal  the  number  of  red  cells  begins  to  diminish,  and  that  this  keeps  up 
for  from  two  to  four  hours,  when  it  is  followed  by  a  gradual  rise  to  the  normal. 
The  usual  fall  is  250,000  to  750,000  per  cubic  millimeter.  These  results 
are  most  marked  after  a  largely  fluid  meal,  and  are  probably  due  to  dilution 
of  the  blood  as  a  result  of  the  absorption  of  fluids.  In  animals  the  number 
of  red  cells  is  increased  by  fasting,  but  in  man  the  results  are  variable,  some 
authorities  claiming  an  increase  and  others  a  decrease.     In  childhood  there 


RED     CORPUSCLES    OR     ERYTHROCYTES 


109 


is  no  difference  between  the  sexes  in  the  number  of  red  cells  per  cubic  milli- 
meter, but  after  menstruation  is  established  a  relative  anemia  develops  in 
women.  YVelcker's  original  estimate  placed  the  difference  at  500,000  per 
cubic  millimeter,  and  these  figures  have  been  generally  accepted,  though 
Leichtenstein  asserts  that  the  difference  is  1,000,000. 

Menstruation  in  healthy  subjects  has  practically  no  effect,  as  not  more 
than  ico-200  cubic  centimeters  of  blood  are  lost  normally  in  the  course  of 


MAMMALS.  - 


IAN  I     WHALE        I    ELEPHANT  MOUSE  HORSE  MUSK   DEER  CAMEL 


rur  m  irwn 


Fio.  in. — The  Illustration  is  Somewhat  Altered  from  a  Drawing  by  Gulliver,  in  the 
Proceed.  Zool.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  in  the  main 
Divisions  of  the  Vertebrata.  The  fractions  are  those  of  an  inch,  and  represent  the  average  diameter. 
In  the  case  of  the  oval  cells,  only  the  long  diameter  is  here  given.  It  is  remarkable,  that  although 
the  size  of  the  red  blood-ceils  varies  so  much  in  the  different  classes  of  the  vertebrate  kingdom, 
that  of  the  white  corpuscles  remains  comparatively  uriform,  and  thus  they  are,  in  some  animals, 
much  greater,  in  others  much  less,  than  the  red  corpuscle  existing  side  by  side  with  them. 


several  days.  Under  such  circumstances  the  normal  diminution  of  red  cells 
per  cubic  millimeter  is  probably  less  than  150,000,  though  Sfameni  has  placed 
the  loss  at  about  225,000.  In  fact  an  increase  has  been  claimed.  The 
leucocytes  are  slightly  increased  during  menstruation.  It  is  now  the  general 
opinion  that  pregnancy  has  little  or  no  effect  on  the  number  of  red  cells,  and 


110  THE     BLOOD 

that  any  anemia  must  be  due  to  abnormal  conditions.  Post-partum  anemia 
should  not  last  longer  than  two  weeks. 

The  red  corpuscles  are  not  all  alike.  In  almost  every  specimen  of  blood 
a  certain  number  of  corpuscles  smaller  than  the  rest  may  be  observed.  They 
are  termed  microcytes,  or  hematoblasts,  and  are  probably  immature  corpuscles. 

A  peculiar  property  of  the  red  corpuscles,  which  is  exaggerated  in  in- 
flammatory blood,  may  be  here  again  noticed,  i.e.,  their  great  tendency  to 
adhere  together  in  rolls  or  columns  (rouleaux),  like  piles  of  coins.  These 
rolls  quickly  fasten  together  by  their  ends,  and  cluster;  so  that,  when  the 
blood  is  spread  out  thinly  on  a  glass,  they  form  a  kind  of  irregular  network, 
with  crowds  of  corpuscles  at  the  several  points  corresponding  with  the  knots 
of  the  net,  figure  109.  Hence  the  clot  formed  in  such  a  thin  layer  of  blood 
looks  mottled  with  blotches  of  pink  upon  a  white  ground. 

The  red  corpuscles  are  constantly  undergoing  disintegration  in  different 
parts  of  the  circulatory  system,  particularly  in  the  spleen.  The  liberated 
hemoglobin  contributes  to  the  formation  of  the  bile  pigments  in  the  liver. 

Development  of  the  Red  Blood-Corpuscles. — The  first  formed 
blood-corpuscles  of  the  human  embryo  differ  much  in  their  general  characters 


Fig.  112. — Part  of  the  Network  of  Developing  Blood-Vessels  in  the  Vascular  Area  of  aGuinea- 
Pig.  bl.  Blood-corpuscles  becoming  free  in  an  enlarged  and  hollowed-out  part  of  the  network;  a, 
process  of  protoplasm.      (E.  A.  Schafer.) 

from  those  which  belong  to  the  later  periods  of  intra-uterine,  and  to  all  periods 
of  extra-uterine  life.     Their  manner  of  origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the  vascular  area, 
in  which  the  first  rudiments  of  the  blood-vessels  and  blood-corpuscles  are 
developed.  Here  the  nucleated  embryonal  cells  of  the  mesoblast,  from 
which  the  blood-vessels  and  corpuscles  are  to  be  formed,  send  out  processes 
in  various  directions,  and  these,  joining  together,  form  an  irregular  mesh- 
work.  The  nuclei  increase  in  number,  and  collect  chiefly  in  the  larger  masses 
of  protoplasm,   but  partly  also  in   the  processes.     It  appears  that  hemo- 


DEVELOPMENT     OF    THE     RED     BLOOD-CORPUSCLES 


111 


globin  then  makes  its  appearance  in  certain  of  these  nucleated  embryonal 
cells,  which  thus  become  the  earliest  red  blood-corpuscles.  The  proto- 
plasm of  the  cells  and  their  branched  network  in  which  these  corpuscles 
lie  then  become  hollowed  out  into  a  system  of  canals  enclosing  fluid,  in  which 
the  red  nucleated  corpuscles  float.  The  corpuscles  at  first  are  from  about 
10  fj,  to  16  /x  in  diameter,  mostly  spherical,  and  with  granular  contents,  and 
a  well-marked  nucleus.     Their  nuclei,  which  are  about  5  /x  in  diameter, 


Fig. 


Fig. 


Fig.  113. — Multiplication  of  the  Nucleated  Red  Corpuscles.  Marrow  of  young  kitten  after 
bleeding,  showing  above  karyokinetic  division  of  erythroblast,  and  below  the  formation  of  mature 
from  immature  erythrocytes.      (Howell.) 

Fig.  114. — Shows  the  Way  in  which  the  Nucleus  Escapes  from  the  Nucleated  Red  Corpuscles. 
1,2,3,  4,  represent  different  stages  of  the  extrusion  noticed  upon  the  living  corpuscles,  a.  Specimen 
from  the  circulating  blood  of  an  adult  cat,  bled  four  times;  b,  specimen  from  the  circulating  blood 
of  a  kitten  forty  days  old,  bled  twice;  c,  specimens  from  the  blood  of  a  fetal  cat,  o  cm.  long.  Others 
from  the  marrow  of  an  adult  cat,  two  of  the  figures  showing  the  granules  present  in  the  corpuscles, 
which  have  been  interpreted  erroneously  as  a  sign  of  the  disintegration  of  the  nucleus.      (Howell.) 

are  central,  circular,  very  little  prominent  en  the  surfaces  of  the  corpuscles, 
and  apparently  slightly  granular. 

The  corpuscles  then  strongly  resemble  the  colorless  corpuscles  of  the 
fully  developed  blood  but  for  their  color.  They  are  capable  of  ameboid 
movement  and  multiply  by  division. 

When,  in  the  progress  of  embryonic  development,  the  liver  is  formed, 
the  multiplication  of  blood-cells  in  the  whole  mass  of  blood  ceases,  and  new 
blood-cells  are  produced  by  this  organ,  and  also  by  the  spleen.  These  are 
at  first  colorless  and  nucleated,  but  afterward  acquire  the  ordinary  blood  tinge, 
and  resemble  very  much  those  of  the  first  set.  They  also  multiply  by  division. 
The  bone  marrow  also  begins  to  form  red  corpuscles,  though  at  first  in  small 
amounts  only.  This  function  develops  rapidly,  however,  so  that  at  birth 
the  marrow  represents  the  chief  seat  of  production  of  the  red  cells.  Never- 
theless, nucleated  red  cells  are  usually  found  at  birth,  sometimes  in  con- 
siderable quantities  in  the  liver  and  in  the  spleen.  Non-nucleated  red  cells 
begin  to  appear  soon  after  the  first  month  of  fetal  life,  and  gradually  increase 
so  that  at  the  fourth  month  they  form  one-fourth  of  the  whole  amount  of 


112  THE     BLOOD 

colored  corpuscles.     At  the  end  of  fetal  life  they  almost  completely  replace 

the  nucleated  cells.     In  late  fetal  life  the  red  cells  are  formed  in  almost  the 
same  way  as  in  extra-uterine  life. 

Various  theories  have  prevailed  as  to  the  mode  of  origin  of  the  non-nu- 
cleated colored  corpuscles.  For  a  time  it  was  thought  that  they  were  of 
endoglobular  origin,  and  merely  fragments  of  some  original  cell,  being  pro? 
duced  by  subdivision  of  the  cell  body  itself.  This  theory  easily  accounted 
for  the  absence  of  the  nuclei,  but  it  has  not  been  supported  by  recent  investi- 
gations. At  present  it  is  the  general  belief  that  the  non-nucleated  celb,  or 
erythrocytes,  are  derived  from  nucleated  cells  by  a  process  of  mitotic  division, 
and  further  that  their  nuclei  gradually  shrink  or  fade  and  are  then  extruded. 


Fig.  nt. — Colored  Nucleated  Corpuscles,  from  the  Red  Marrow  of   the  Guinea-Pig.      (E.  A. 

Schafer.) 

The  use  of  some  of  the  more  recent  stains  seems  to  prove  that  there  are  traces 
of  nuclear  material  in  the  non-nucleated  corpuscles. 

After  infancy  and  early  childhood  the  origin  of  erythrocytes  is  practically 
limited  to  the  red  marrow  of  the  bones.  The  mother  cells,  or  erythroblasts, 
are  constantly  forming  and  setting  free  erythrocytes,  the  rate  varying  greatly 
at  different  periods. 

The  Colorless  Corpuscles  or  Leucocytes.  In  human  blood  the 
white  corpuscles,  leucocytes,  are  nearly  spherical  masses  of  granular  proto- 
plasm without  cell  wall.  In  all  cases  one  or  more  nuclei  exist  in  each  cor- 
puscle.    The  corpuscles  vary  considerably  in  size  but  average  10  fx  in  diameter. 

The  number  of  leucocytes  in  a  cubic  millimeter  of  blood  is  estimated 
at  7,500  to  8,000.  The  proportion  of  white  corpuscles  to  red,  therefore,  is 
about  one  of  the  former  to  700  of  the  latter.  This  proportion  is  not  very 
constant  in  health  and  great  variations  cccur  under  the  influence  of  disease, 
especially  in  certain  infectious  diseases  in  which  the  number  of  white  corpus- 
cles is  markedly  increased. 

After  a  full  meal  the  white  cells  in  a  healthy  adult  are  increased  in  number 
about  one-third,  the  increase  beginning  within  an  hour,  attaining  a  maxi- 
mum in  three  or  four  hours,  and  then  gradually  falling  to  normal.  This 
process  is  frequently  modified  by  the  character  of  the  food,  the  greatest 
increase  occurring  with  an  exclusively  meat  diet,  while  a  purely  vegetarian 
diet  has  usually  no  effect.  The  increase  is  also  more  marked  in  children, 
and  especially  in  infants.  The  essential  factor  is  probably  the  absorption 
of  albuminous  matter  in  considerable  quantities.  This  causes  proliferation 
of  leucocytes  in  the  adenoid  tissue  of  the  gastro-intestinal  tract. 

In  pregnancy  there  is  often  a  moderate  increase  in  the  number  of  white 


THE  COLORLESS  CORPUSCLES  OR  LEUCOCYTES         113 

cells  during  the  later  months.  This  does  net  begin  until  after  the  third 
month,  and  is  most  marked  and  constant  in  primipara?.  After  parturition 
the  leucocytes  gradually  diminish  under  normal  conditions,  and  usually 
reach  the  normal  within  a  fortnight.  The  essential  factor  is  probably  the 
general  stimulation  in  the  maternal  organism.  It  is  well  established  that  the 
white  cells  are  very  numerous  in  the  new-born,  though  different  observers 
have  made  very  conflicting  estimates.  Still  all  agree  that  there  is  a  very 
rapid  decrease  in  their  numbers  during  the  first  few  days,  and  that  this  is 
followed  by  a  less  marked  increase,  which  continues  for  many  months. 
According  to  Rieder,  who  is  perhaps  the  most  reliable,  there  are  at  birth 
from  14,200  to  27,400  per  cubic  millimeter,  and  after  the  fourth  day  from 
12,400  to  14,800. 

Varieties  of  Leucocytes.  The  colorless  corpuscles  present  greater  diversi- 
ties of  form  than  the  red  ones,  plate  II.  They  are  usually  classified  according 
to  their  reaction  to  staining  agents,  or  to  the  presence  or  absence  of  granules 
in  their  cytoplasm.  Kanthack  and  Hardy  offer  the  following  classification, 
based  upon  both  phenomena: 

Leucocytes. 

A .  Oxvphile  (staining  with  acid  dyes) ....  J  x"  finely  granular. 

I  2.  Coarsely  granular  eosinophile. 

B.  Basophile  (staining  with  basic  dyes)  . .      1.  Finely  granular. 

C.  Hyaline J  '■  Sma11  lymphocyte. 

( 2.  Large  myelocyte. 

The  finely  granular  oxyphile  constitutes  75  per  cent  of  all  leucocytes. 
It  has  an  average  diameter  of  10  ji,  and  possesses  phagocytic  action  to  a 
marked  degree — that  is,  it  possesses  the  power  of  ingesting  foreign  particles. 
Its  nucleus  consists  of  several  lobes  united  by  threads  of  chromatin.  This 
cell  was  formerly  known  under  the  term  neutrophile,  because  of  its  supposed 
reaction  to  neutral  dyes. 

The  coarsely  granular  form  of  eosinophile  constitutes  only  2  per  cent  of 
the  leucocytes.     It  has  a  diameter  of  12  [l  and  a  reniform  nucleus. 

The  basophile  cell  is  rarely  found  in  normal  blood.  It  may  occur  occa- 
sionally during  periods  of  digestion.  It  is  a  small,  spherical  cell,  with  an 
irregular  nucleus  and  a  diameter  of  7  fi. 

The  small  hyaline  leucocyte  is  also  called  a  lymphocyte,  because  of  the 
large  numbers  found  in  adenoid  tissue,  and  is  supposed  to  be  an  immature 
form.  The  nucleus  is  proportionally  large,  and  is  surrounded  by  but  little 
protoplasm  in  which  no  granules  can  be  detected.  The  cell  is  about  the 
size  of  a  red  blood-cell,  and  constitutes  from  10  to  20  per  cent  of  all  leucocytes. 

The  large  hyaline  or  myelocyte  varies  in  diameter  from  8.5  to  10  fx.  Its 
nucleus  is  spherical  or  reniform,  and  is  surrounded  by  more  protoplasm  than 
in  the  case  of  the  lymphocyte.     It  forms  about  10  per  cent  of  the  leucocytes. 

Ameboid  Movement  of  Leucocytes.  The  remarkable  property  of  the  color- 
8 


114 


THE     BLOOD 


less  corpuscles  of  spontaneously  changing  their  shape  was  first  demonstrated 
by  Wharton  Jones  in  the  blood  of  the  skate.  If  a  drop  of  blood  be  examined 
with  a  high  power  of  the  microscope,  under  conditions  by  which  loss  of  mois- 
ture is  prevented,  and  at  the  same  time  the  temperature  is  maintained  at 
about  that  of  the  body,  370  C,  the  colorless  corpuscles  will  be  observed 
slowly  to  alter  their  shapes,  and  to  send  out  processes  at  various  parts  of  their 


f 


Fig.  116. — (a)  Red  blood- corpuscle  for  comparison;  (£>)  small  hyaline  cell  or  lymphocyte; 
(c)  large  hyaline  cell  or  myelocyte;  (d)  fine  granular  oxyphile;  (e)  coarse  granular  oxyphile  or  eosino- 
phile;    (/)  basophile.      (F.  C.  Busch.) 

circumference.  The  ameboid  movement  which  can  be  demonstrated  in 
human  colorless  blood-corpuscles,  can  be  most  conveniently  studied  in  the 
newt's  blood.  Processes  are  sent  out  from  the  corpuscle.  These  may  be 
withdrawn,  but  more  often  the  protoplasm  of  the  whole  corpuscle  flows 
gradually  forward  to  the  position  occupied  by  the  process,  thus  the  corpuscle 
changes  its  position.  The  change  of  position  of  the  corpuscle  can  also  take 
place  by  a  flowing  movement  of  the  whole  mass,  and  in  this  case  the  loco- 


Fig.  117. — Human  Colorless  Blood-Corpuscle,  Showing  its  Successive  Changes  of  Outline  Within 
Ten  Minutes  when  kept  Moist  on  a  Warm  Stage.    (Schofield.) 

motion  is  comparatively  rapid.  The  activity  both  in  the  processes  of  change 
of  shape  and  also  of  change  in  position  is  much  more  marked  in  some  cor- 
puscles than  in  others.  Klein  states  that  in  the  newt's  blood  the  changes 
are  especially  noticeable  in  a  variety  of  the  colorless  corpuscle,  which  consists 
of  a  mass  of  finely  granular  protoplasm  with  jagged  outline  and  contains 


CHEMICAL     COMPOSITION     OF    THE     BLOOD 


115 


three  or  four  nuclei,  or  in  large  irregular  masses  of  protoplasm  containing 
from  five  to  twenty  nuclei. 

The  property  which  the  colorless  corpuscles  possess  of  passing  through 
the  walls  of  the  blood-vessels  will  be  described  later  on. 

The  Blood  Plates  or  Thrombocytes.  A  third  variety  of  corpuscle 
found  in  the  blood  is  known  as  the  blood  plate.  They  are  circular  or  elliptical 
in  shape,  of  nearly  homogeneous  structure,  and  vary  in  size  from  0.5  to  5^. 


.     Fig.  118. — Blood  Plates,  Showing  Chromatic  Centers  Regarded  by  some  as  Nuclei,  and   Ex- 
hibiting Ameboid  Movement.      (Schaier,  from  Kopsch.) 

■Hence  they  are  smaller  than  the  red  corpuscles.  They  vary  in  number  from 
5,000  to  45,000  per  cubic  millimeter  and  are  preserved  by  drawing  fresh 
blood  directly  into  Hayem's  or  other  preserving  fluid.  Chemically  they 
contain  a  nucleo-proteid,  and  it  is  supposed  that  they  take  part  in  the  phe- 
nomenon of  coagulation.  According  to  Deetjen  and  others,  ameboid  move- 
ment has  been  demonstrated  in  these  bodies. 


CHEMICAL    COMPOSITION    OF    THE    BLOOD. 

In  considering  the  chemical  composition  of  the  blood,  it  will  be  convenient 
to  take  in  order  the  composition  of  the  various  chief  factors  into  which  the 
blood  may  be  separated,  viz.,  The  Plasma  ;  The  Serum  ;  The  White  Cor- 
puscles ;    The  Red  Corpuscles. 

The  Composition  of  the  Plasma.  The  plasma  is  the  liquid  part 
of  the  blood  in  which  the  corpuscles  float. 

It  contains  the  fibrin  factors,  inasmuch  as  when  drawn  from  the  blood- 
vessels it  undergoes  coagulation  and  splits  up  into  fibrin  and  serum.  It 
differs  from  the  serum  in  containing  fibrinogen,  but  in  appearance  and  in 
reaction  it  closely  resembles  that  fluid.  Its  alkalinity,  however,  is  greater 
than  that  of  the  serum  obtained  from  it.  It  may  be  freed  from  corpuscles 
by  the  centrifugal  machine,  or  by  the  other  means  enumerated  below.    . 


116  THE     BLOOD 

The  chief  methods  of  obtaining  plasma  free  from  corpuscles  are:  i.  By  cold.  The 
temperature  should  be  about  o°  C.  and  may  be  two  or  three  degrees  higher,  but  not 
lower.  2.  The  addition  of  neutral  salts,  in  certain  proporticn,  either  as  solids  or  in 
solution,  e.g.,  of  sodium  sulphate,  if  solid  i  part  to  12  parts  of  blood;  if  a  saturated  solu- 
tion 1  part  to  6  parts  of  blood.  Or  magnesium  sulphate,  saturated  solution  1  part  to 
4  of  blood.  3.  By  mixing  frog's  blood  with  an  equal  part  of  a  5  per  cent  solution  of 
cane  sugar,  and  getting  rid  of  the  corpuscles  by  filtration.  4.  By  the  injection  of  com- 
mercial peptone  into  the  veins  of  certain  mammals  previous  to  bleeding  them  to  death, 
allowing  the  corpuscles  to  subside  or  by  subjecting  the  blood  to  the  action  of  a  centrif- 
ugal machine  by  the  rapid  rotation  of  which  the  whole  of  the  solids  are  driven  to  the 
outer  end  of  the  tubes  in  which  the  blood  is  placed. 

Percentage  Composition  of  Plasma. 

Water 90.29 

Solids — 

1.  Proteids — 
Fibrinogen  1 

Paraglobulin         - 8.289 

Serum  albumin   ) 

2.  Extractives 566 

3.  Inorganic  salts 8  ;o 

9.71 

100.00 

Water.  The  water  of  the  plasma  varies  in  amount  according  to  the 
amount  of  food,  drink,  and  exercise,  or  other  circumstances.  It  amounts 
to  about  90  per  cent. 

Proteids.  Fibrinogen  is  the  substance  in  plasma  which  is  converted  into 
fibrin  on  coagulation.  It  belongs  to  the  class  of  proteids  called  globulins. 
It  is  precipitated  from  plasma  with  serum  globulin  by  saturation  with  MgS04 
and  NaCl.  It  is  soluble  in  dilute  salt  solutions  but  is  not  soluble  in  water. 
It  can  be  distinguished  from  serum  globulin  by  a  number  of  special  reactions; 
1.  Its  coagulation  temperature  is  lower,  550  to  560  C.  2.  It  is  completely 
precipitated  by  saturation  with  NaCl  as  well  as  with  MgS04.  3.  It  gives 
rise  to  an  insoluble  proteid,  fibrin.  It  may  be,  however,  that  fibrinogen  is 
not  a  simple  proteid,  but  a  mixture  or  loose  chemical  combination  of  two 
or  more  proteids.  Fibrinogen  is  present  in  plasma  to  the  extent  of  0.2  to 
0.5  per  cent. 

Serum  globulin  or  paraglobulin  is  similar  to  fibrinogen  in  its  reactions. 
It  is  completely  precipitated  by  MgS04;  incompletely  by  NaCl,  and  co- 
agulates at  a  temperature  of  750  C.  It  is  likewise  soluble  in  dilute  salt  solu- 
tions but  insoluble  in  water.     It  is  present  in  plasma  in  from  3.5  to  4  per  cent. 

Serum  albumin  is  the  proteid  which  predominates  in  human  plasma. 
It  is  readily  obtained  in  crystalline  form;  is  soluble  in  MgS04  and  NaCl 
solutions,  but  insoluble  in  saturated  ammonium  sulphate  solutions;  and 
coagulates  in  neutral  or  acid  solutions  at  from  730  to  750  C. 

Extractives.  The  extractives  are  the  nitrogen-containing  substances 
such  as  urea,  uric  acid,  creatin,  creatinin,  etc.;    glycogen,  dextrose,  choles- 


THE    COMPOSITION    OF    THE    WHITE    CORPUSCLES  117 

terin,  etc.,  a  total  of  0.5  to  0.6  per  cent.  The  dextrose  content  amounts 
to  from  0.1  to  0.15  per  cent. 

Ferments  are  also  found  in  blood;  first,  a  diastatic  ferment  converting 
amyloids  into  sugars;  second,  a  glycolytic  ferment  causing  a  disappearance 
of  sugar;  third,  a  fat-splitting  ferment,  lipase;  and  fourth,  fibrin  ferment 
(thrombin),  or  its  precursor,  prothrombin. 

Inorganic  Substances.  The  blood  plasma  contains  about  0.8  per  cent 
of  inorganic  salts  distributed  as  follows,  the  sodium  chloride  predominating: 

Parts  in  1,000  of  plasma. 

Chlorine 3-536 

Sulphuric  acid 129 


Phosphoric   acid 

Potassium 

Sodium 

Phosphate  of  lime 

Phosphate  of   magnesia. 
Oxygen 


MS 
314 
410 
298 
218 
455 


S.505 


The  Serum.  The  serum  is  the  liquid  part  of  the  blood  or  of  the 
plasma  which  remains  after  the  fibrin  has  been  formed  and  removed.  It  is 
a  transparent,  yellowish,  faintly  alkaline  fluid,  with  a  specific  gravity  of 
from  1025  to  1032.  Serum  may  be  obtained  from  blood-corpuscles  by  allow- 
ing blood  to  clot  in  large  test  tubes,  or  by  subjecting  test  tubes  of  whipped 
blood  to  the  action  of  a  centrifugal  machine  for  some  time.  Serum  is  chemi- 
cally very  much  the  same  as  plasma  except  that  it  has  lost  the  fibrinogen  in 
the  process  of  clotting  and  has  gained  the  by-products  of  that  process — throm- 
bin, thrombokinase,  and  fibrin-globulin.  The  salts  of  serum  are  practically 
those  of  plasma. 

The  Composition  of  the  White  Corpuscles.  The  white  corpuscles 
are  comparatively  undifferentiated  cellular  elements,  hence  possess  the  chemi- 
cal composition  of  protoplasm.  Lillienfeld  has  made  an  analysis  of  the 
leucocytes  of  thymus  gland  from  the  calf,  which  contain  11.49  Per  cer*t  °f 
solids,  as  follows: 

In  100  Parts  0}  Dry  Substance  0}  Corpuscles  oj  Calf. 

Per  cent. 

Proteid 1 .  76 

Leuconuclein 68 .  78 

Histon 8.76 

Lecithin 7-51 

Fat 4.02 

Cholesterin 4 .  40 

Glycogen 0.80 

96.03 


118  THE     BLOOD 

The  most  noteworthy  substance  in  this  table  is  the  nucleohiston  content, 
first  isolated  by  Kossel  and  Lillienfeld.  Beside  the  substances  in  the  above 
table,  the  white  corpuscles  contain  salts  of  potassium,  sodium,  calcium,  and 
magnesium.     The  potassium  phosphate  is  present  in  greatest  amount. 

The  Composition  of  the  Red  Corpuscles.  Analysis  of  a  thousand 
parts  of  moist  blood-corpuscles  shows  the  following  result: 

Water 688 

Solids — 

Organic 303. 88  ) 

■mt-         1  of  312  =  1,000 

Mineral 8.12  )  ° 

Of  the  solids  the  most  important  is  Hemoglobin,  the  substance  to  which 
the  blood  owes  its  color.  It  constitutes,  as  will  be  seen  from  the  appended 
table,  more  than  90  per  cent  of  the  organic  matter  of  the  corpuscles.  Be- 
sides hemoglobin  the  corpuscles  contain  proteid  and  fatty  matters,  the  former 
chiefly  consisting  of  globulins,  and  the  latter  of  cholesterin  and  lecithin. 

In  1,000  parts  of  organic  matter  are  found: 

Hemoglobin 905 . 4 

Proteids 86. 7 

Fats 7.9  =  1,000 

Of  the  inorganic  salts  of  the  corpuscles,  the  iron  omitted,  there  are  present, 
in  1,000  parts  of  corpuscles  (Schmidt): 

Potassium  chloride 3 .  679 

Potassium  phosphate 2 .  343 

Potassium  sulphate 132 

Sodium  phosphate 633 

Calcium  phosphate 094 

Magnesium   phosphate 060 

Soda 341  =  7.282 

Hemoglobin.  Of  the  substances  in  the  erythrocytes,  by  far  the 
most  important  from  every  point  of  view  is  the  pigment,  hemoglobin.  It 
composes  about  90  per  cent  of  the  total  solids  of  the  corpuscles;  there- 
fore, between  14  and  15  per  cent  of  the  blood  itself.  Hemoglobin  is  the  most 
complex  compound  in  the  body,  having  a  molecule  of  the  enormous  molec- 
ular weight  of  16,669.  Hemoglobin  is  intimately  distributed  throughout 
the  stroma  of  the  corpuscle,  and  when  dissolved  out  it  undergoes  crystallization. 

Its  percentage  composition  is  C  53.85;  H  7.32;  N  16.17;  O  21.84; 
S  0.63;  Fe  0.42.  Jacquet  gives  the  empirical  formula  for  the  hemoglobin 
of  the  dog,  C758H1203N195S3FeO218.  The  most  interesting  of  the  properties 
of  hemoglobin  are  its  powers  of  crystallizing  and  its  attraction  for  oxygen 
and  other  gases. 

Hemoglobin  Crystals.  The  hemoglobin  (oxyhemoglobin)  of  the  blood  of 
various  animals  possesses  the  power  of  crystallizing  to  very  different  ex- 


HEMOGLOBIN 


119 


tents.  In  some  the  formation  of  crystals  is  almost  spontaneous,  whereas 
in  others  it  takes  place  either  with  great  difficulty  or  not  at  all.  Among 
the  animals  whose  blood  coloring-matter  crystallizes  most  readily  are  the 
guinea-pig,  rat,  squirrel,  and  dog;  and  in  these  cases  to  obtain  crystals  it 
is  generally  sufficient  to  dilute  a  drop  of  recently  drawn  blood  with  water 


Fig.  119. — Crystals  of  Oxyhemoglobin — Prismatic,  from  Human  Blood. 

and  to  expose  it  for  a  few  minutes  to  the  air.  In  many  instances  other  means 
must  be  adopted,  e.g.,  the^  addition  of  alcohol,  ether,  or  chloroform,  rapid 
freezing,  and  then  thawing,  the  application  of  an  electric  current,  a  tempera- 


a 


1ST  ■  -■%■■• 


Fig.  120. — Oxyhemoglobin  Crystals — Tetrahedral,  from  Blood  of  the  Guinea-pig. 


ture  of  6o°  C,  the  addition  of  sodium  sulphate,  or  the  addition  of  decom- 
posing serum  of  another  animal. 

The  hemoglobin  of  human  blood  crystallizes  with  difficulty,  as  does  also 
that  of  the  ox,  the  pig,  the  sheep,  and  the  rabbit. 


120  THE     BLOOD 

The  forms  of  hemoglobin  crystals,  as  will  be  seen  from  figures  119  and 
120,  differ  greatly.  Hemoglobin  crystals  are  soluble  in  water.  Both  the 
crystals  themselves  and  also  their  solutions  have  the  characteristic  color  of 
arterial  blood. 

A  dilute  solution  of  oxyhemoglobin  gives  a  characteristic  appearance 
with  the  spectroscope.  Two  absorption  bands  are  seen  between  the  solar 
lines  D,  which  is  the  sodium  band  in  the  yellow,  and  E,  see  the  frontispiece, 
one  in  the  yellow,  with  its  middle  line  some  little  way  to  the  right  of  D.  This 
band  is  very  intense,  but  narrower  than  the  other,  which  lies  in  the  green 
near  to  the  left  of  E.  Each  band  is  darkest  in  the  middle  and  fades  away 
at  the  sides.  As  the  strength  of  the  solution  increases,  the  bands  become 
broader  and  deeper.  Both  the  red  and  the  blue  ends  of  the  spectrum  be- 
come encroached  upon  until  the  bands  coalesce  to  form  one  very  broad  band 
when  only  a  slight  amount  of  the  green  and  part  of   the  red  remain  unab- 


Fig.  121. — Hexagonal  Oxyhemoglobin  Crystals,  from  Blood  of  Squirrel.  On  these  hex- 
agonal plates  prismatic  crystals,  grouped  in  a  stellate  manner,  not  unfrequently  occur  (after  Funke). 

sorbed.  Any  further  increase  of  strength  leads  to  complete  absorption  of 
the  spectrum. 

If  crystals  of  hemoglobin  are  exposed  to  an  atmosphere  of  oxygen  they 
take  up  oxygen  and  form  oxyhemoglobin,  each  gram  of  the  pigment  fixing 
a  definite  amount  of  oxygen,  see  chapter  on  Respiration.  When  subjected 
to  a  mercurial  air  pump  the  oxygen  is  given  off,  and  the  crystals  become 
of  a  purple  color.  A  solution  of  the  oxyhemoglobin  in  the  blood-corpuscles 
may  be  made  to  give  up  oxygen,  and  to  change  color  in  a  similar  manner. 
One  gram  of  oxyhemoglobin  liberates  1.59  c.c.  oxygen,  or  according  to  Hiif- 
ner's  later  determinations,  1.34  c.c. 

This  change  may  be  also  effected  by  passing  through  the  solution  of 
blood  or  of  oxyhemoglobin,  hydrogen  or  nitrogen  gas,  or  by  the  action  of 


ACTION    OF    GASES    ON     HEMOGLOBIN  121 

reducing  agents,  of  which  Stokes's  fluid*  or  ammonium  sulphide  are  the 
most  convenient. 

With  the  spectroscope,  a  solution  of  deoxidized  or  reduced  hemoglobin 
is  found  to  give  an  entirely  different  appearance  from  that  of  oxidized  hemo- 
globin. Instead  of  the  two  bands  at  D  and  E  we  find  a  single  broader  but 
fainter  band  occupying  a  position  midway  between  the  two,  and  at  the  same 
time  less  of  the  blue  end  of  the  spectrum  is  absorbed.  Even  in  strong  solu- 
tions this  latter  appearance  is  found,  thereby  differing  from  the  strong  solu- 
tion of  oxidized  hemoglobin  which  lets  through  only  the  red  and  orange 
rays;  accordingly,  to  the  naked  eye  the  one  (reduced-hemoglobin  solution) 
appears  purple,  the  other  (oxyhemoglobin  solution)  red.  The  deoxidized 
crystals  or  their  solutions  quickly  absorb  oxygen  on  exposure  to  the  air, 
becoming  scarlet.  If  solutions  of  blood  be  taken  instead  of  solutions  of 
hemoglobin,  results  similar  to  the  whole  of  the  foregoing  can  be  obtained. 

Venous  blood  never,  except  in  the  last  stages  of  asphyxia,  fails  to  show 
the  oxyhemoglobin  bands,  inasmuch  as  the  greater  part  of  the  hemoglobin 
even  in  venous  blood  exists  in  the  more  highly  oxidized  condition. 

Action  of  Gases  on  Hemoglobin.  Carbonic  oxide  gas  passed 
through  a  solution  of  hemoglobin  causes  it  to  assume  a  cherry-red  color  and 
to  present  a  slightly  altered  spectrum;  two  bands  are  still  visible  but  are 
slightly  nearer  the  blue  end  than  those  of  oxyhemoglobin,  see  plate  I.  The 
amount  of  carbonic  oxide  taken  up  is  equal  to  the  amount  of  the  oxygen 
displaced.  Although  the  carbonic-oxide  gas  readily  displaces  oxygen,  the 
reverse  is  not  the  case,  and  upon  this  property  depends  the  dangerous  effect 
of  coal-gas  poisoning.  Coal-gas  contains  much  carbonic  oxide,  and,  when 
breathed,  the  gas  combines  with  the  hemoglobin  of  the  blood  and  produces 
a  compound  which  cannot  easily  be  reduced.  This  compound  (carboxyhemo- 
globin)  is  not  an  oxygen-carrier,  and  death  may  result  from  suffocation  due 
to  the  want  of  oxygen,  notwithstanding  the  free  entry  of  pure  air  into  the 
lungs.  Crystals  of  carbonic-oxide  hemoglobin  closely  resemble  in  form  those 
of  oxyhemoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide  hemo- 
globin, which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxyhemoglobin,  and  therefore  leaves  the  reduced 
hemoglobin  in  a  condition  actively  to  take  up  oxygen. 

Sulphuretted  hydrogen,  if  passed  through  a  solution  of  oxyhemoglobin, 
reduces  it  and  an  additional  band  appears  in  the  red.  If  the  solution  be 
then  shaken  with  air,  the  two  bands  of  oxyhemoglobin  replace  that  of  re- 
duced hemoglobin,  but  the  band  in  the  red  persists. 

*  Stokes's  Fluid  consists  of  a  solution  of  ferrous  sulphate,  to  which  ammonia  has  been 
added  and  sufficient  tartaric  acid  to  prevent  precipitation.  Another  reducing  agent  is  a 
solution  of  stannous  chloride,  treated  in  a  way  similar  to  the  ferrous  sulphate,  and  a  third 
reagent  of  like  nature  is  an  aqueous  solution  of  yellow  ammonium  sulphide,  NH4HS. 


122  THE     BLOOD 

Methemoglobin.  If  an  aqueous  solution  of  oxyhemoglobin  is  ex- 
posed to  the  air  for  some  time,  its  spectrum  undergoes  a  change;  the  two 
d  and  e  bands  become  faint,  and  a  new  line  in  the  red  at  c  is  developed.  The 
solution,  too,  becomes  brown  and  acid  in  reaction,  and  is  precipitable  by  basic 
lead  acetate.  This  change  is  due  to  the  decomposition  of  oxyhemoglobin, 
and  to  the  production  of  methemoglobin.  On  adding  ammonium  sulphide, 
reduced  hemoglobin  is  produced,  and  on  shaking  this  up  with  air,  oxyhemo- 
globin is  again  produced.  Methemoglobin  is  probably  a  stage  in  the  deoxida- 
tion  of  oxyhemoglobin.     It  appears  to  contain  less  oxygen  than  oxyhemo- 


tiu.  122. — rleischl's  Hemoglobinometer. 

globin,  but  more  than  reduced  hemoglobin.     Its  oxygen  is  in  more  stable 
combination,  however,  than  is  the  case  with  the  former  compound. 

Estimation  of  Hemoglobin.  The  most  exact  method  is  by  the  esti- 
mation of  the  amount  of  iron  (dry  hemoglobin  containing  0.42  per  cent 
of  iron)  in  a  given  specimen  of  blood,  but  as  this  is  a  somewhat  complicated 
process,  various  methods  have  been  proposed  which,  though  not  so  exact, 
have  the  advantage  of  simplicity.  Of  the  several  varieties  of  hemoglobinom- 
eter, one  of  the  best  adapted  to  its  purpose  is  that  invented  by  Professor 
Fleischl,  of  Vienna.  In  this  instrument  the  amount  of  hemoglobin  in  a 
solution  of  blood  is  estimated  by  comparing  a  stratum  of  diluted  blood  with 
a  standard  solid  substance  of  uniform  tint  similar  spectroscopically  to  diluted 
blood.  The  Fleischl  instrument  has  been  recently  modified  and  made  more 
accurate  by  Miescher.  The  Fleischl-Miescher  apparatus  consists  of  a 
stand  with  a  metal  plate  having  a  circular  opening  and  a  plaster  mirror  below, 
S,  figure  122,  which  casts  light  through  the  opening.  Beneath  the  plate  is  a 
metal  framework  containing  a  colored  glass  wedge,  and  along  the  side  of 


ESTIMATION     OF     HEMOGLOBIN  123 

the  same  is  a  scale  graduated  so  as  to  indicate  the  percentage  of  hemoglobin 
corresponding  to  the  shades  of  the  different  parts  of  the  wedge.  This  frame- 
work can  be  moved  by  the  wheel  T  which  fits  into  a  rack  on  its  lower  surface. 
The  scale  can  be  read  through  a  small  opening  M  in  the  plate.  Into  the 
large  circular  opening  of  the  plate  fits  a  cylindrical  metal  cell  G  with  a  glass 
bottom  and  divided  by  a  metal  partition  into  two  equal  parts.  One  of  these 
halves  lies  over  the  wedge  and  is  filled  with  distilled  water.  The  other  con- 
tains the  solution  of  blood  in  which  the  hemoglobin  is  to  be  estimated.  The 
apparatus  is  usually  supplied  with  three  cells.  Of  these,  the  first  two  are 
used  in  estimating  the  hemoglobin  according  to  Miescher's  modification 
of  Fieischl's  original  method.  This  is  the  method  now  generally  used. 
These  cells  are  furnished  with  a  glass  cover  having  a  groove  which  fits 
upon  the  partition  of  the  cell.  Over  this  cover  is  placed  a  diaphragm 
with  a  longitudinal  slit,  which  only  permits  of  the  central  part  of  each 
side  of  the  cell  being  seen.  The  third  cell  is  for  use  when  the  original 
Fleischl  method  is  employed. 

The  patient's  ear  or  finger  is  pricked,  and  the  blood  from  the  wound 
sucked  up  into  the  graduated  pipet  until  it  reaches  the  mark  -,  §,  or  {,  a 
one  per  cent  solution  of  sodium  carbonate  is  then  sucked  in  until  the  upper 
mark  is  reached.  The  pipet  is  then  well  shaken  in  order  to  mix  the  blood 
thoroughly.  One-half  of  each  of  the  two  cells,  which  are  respectively  12 
and  15  millimeters  high,  are  then  filled  with  the  mixture,  the  other  half 
being  filled  with  water.  An  important  point  is  that  the  liquids  should  com- 
pletely fill  the  cells.  The  cover-glasses  and  diaphragms  are  then  applied 
and  the  cells  are  ready  for  examination.  This  must  be  done  by  artificial 
light.  Moreover,  in  order  to  have  accurate  results,  light  of  the  same  inten- 
sity should  be  always  used.  One  of  the  cells  is  placed  on  the  plate  and  the 
wheel  T  turned  until  the  colors  of  the  two  halves  exactly  correspond.  When 
this  point  is  reached,  the  result  is  read  off  on  the  scale  through  the  opening  M. 
This  should  be  repeated  several  times  with  each  of  the  cells,  and  the  average 
of  the  readings  taken.  The  result  obtained  with  the  12-millimeter  cell 
should  be  multiplied  by  J  to  bring  it  up  to  that  of  the  larger.  For  example, 
suppose  the  result  of  several  readings  to  be: 

With  the  large   cell  (15  mm.) 54-°° 

With  the  small  cell  (12  mm.) 42.00 

If  the  readings  obtained  with  the  large  cell  are  exactly  correct,  then  the  read- 
ings with  the  smaller  one  should  be  43.2,  since  54  X  1=43.2.  Or,  if  the 
readings  with  the  smaller  cells  are  exact,  the  readings  with  the  larger  should 
be  52.5,  since  42X1=52.5.  Hence  the  mean  of  54  and  52.5,  namely  53.25, 
should  be  taken  as  the  correct  figure.  On  looking  at  the  corrected  table  of 
hemoglobin  values  supplied  with  each  instrument,  we  would  find  that  this 
number  on  the  scale  corresponds   to   a    solution  containing  400  milligrams 


121  THE     BLOOD 

of  hemoglobin  per  1,000  cubic  centimeters  of  solution.  But  our  original 
dilution  was  either  i  :  200,  1  :  300,  or  1  :  400,  according  as  our  pipet  had  been 
filled  with  blood  up  to  the  mark  },  §,  or  \ ;  so  that  in  order  to  obtain  the  actual 
percentage  of  hemoglobin  in  the  blood  under  examination  we  should  be 
obliged  to  multiply  our  result  by  200,  300,  or  400.  In  the  example  we  have 
taken,  the  amount  of  hemoglobin  would  be,  if  our  dilution  was  1  :  200,  400  X 
200=80,000  milligrams  =  8o  grams  in  1,000  cubic  centi meters  =  8  grams 
in  100  cubic  centimeters,  or  8  per  cent. 

Another  very  simple  method  of  approximately  determining  the  hemo- 
globin percentage  is  the  hemoglobin  scale  devised  by  T.  \Y.  Talquist.  This 
consists  of  a  series  of  shades  of  color  corresponding  to  undiluted  blood  of 
various  hemoglobin  values,  ranging  from  ten  to  one  hundred  per  cent  of  an 
arbitrary  scale.  This  scale  is  included  in  a  book,  the  remaining  pages  of 
which  consist  of  filter  paper,  which  is  used  for  absorbing  the  specimen  of 
blood  whose  hemoglobin  percentage  is  to  be  estimated.  The  blood-stained 
filter  paper  is  compared  with  the  hemoglobin  scale  by  direct  daylight  until 
a  shade  is  found  with  which  it  corresponds.  For  approximate  results  this 
method  has  proved  very  satisfactory. 

Derivatives  of  Hemoglobin.  Hematin.  By  the  action  of  heat  cr 
of  acids  or  alkalies  in  the  presence  of  oxygen,  hemoglobin  can  be  split  up 
into  a  substance  called  Hematin,  which  contains  all  the  iron  of  the  hemo- 
globin from  which  it  was  derived,  and  a  proteid  residue.  Of  the  latter  it  is 
impossible  to  say  more  than  that  it  probably  consists  of  one  or  more  bodies 
of  the  globulin  class.  If  there  be  no  oxygen  present,  instead  of  hematin  a 
body  called  hemochromogen  is  produced,  which,  however,  will  speedily  under- 
go oxidation  into  hematin. 

Hematin  is  a  dark  brownish  or  black  non-crystallizable  substance  of 
metallic  luster.  Its  percentage  composition  is  C,  64.30;  H,  5.50;  N,  9.06; 
Fe,  8.82;  O,  12.32;  which  gives  the  formula  C6oH70N8Fe2O10  (Hoppe- 
Seyler).  It  is  insoluble  in  water,  alcohol,  and  ether;  soluble  in  the  caustic 
alkalies;  soluble  with  difficulty  in  hot  alcohol  to  which  is  added  sulphuric 
acid.  The  iron  may  be  removed  from  hematin  by  heating  it  with  fuming 
hydrochloric  acid  to  1600  C,  and  a  new  body,  hematoporphyrin,  the  so-called 
iron-free  hematin,  is  produced.  Hematoporphyrin  (QgH^NgOij,  Hoppe- 
Seyler)  may  also  be  obtained  by  adding  blood  to  strong  sulphuric  acid,  and 
if  necessary  filtering  the  fluid  through  asbestos.  It  forms  a  fine  crimson 
solution,  which  has  a  distinct  spectrum,  viz.,  a  dark  band  just  beyond  D, 
and  a  second  all  but  midway  between  D  and  E.  It  may  be  precipitated  from 
its  acid  solution  by  adding  water  or  by  neutralization,  and  when  redissolved 
in  alkalies  presents  four  bands,  a  pale  band  between  C  and  D,  a  second 
between  D  and  E,  nearer  D,  another  nearer  E,  and  a  fourth  occupying  the 
chief  part  of  the  space  between  b  and  F. 

Hematin   in  Acid  Solution.      If   an  excess  of  acetic   acid   is  added  to 


DERIVATIVES     OF     HEMOGLOBIN  125 

blood,  and  the  solution  boiled,  the  color  alters  to  brown  from  decomposition 
of  hemoglobin  and  the  setting  free  of  hematin;  by  shaking  this  solution 
with  ether,  a  solution  of  hematin  in  acid  solution  is  obtained.  The  spectrum 
of  the  ethereal  solution  shows  no  less  than  four  absorption  bands,  viz.,  one 
in  the  red  between  C  and  D,  one  faint  and  narrow  close  to  D,  and  then  two 
broader  bands,  one  between  D  and  E,  and  another  nearly  midway  between 
b  and  F.  The  first  band  is  by  far  the  most  distinct,  and  the  acid  aqueous 
solution  of  hematin  shows  it  plainly. 

Hematin  in  Alkaline  Solution.  If  a  caustic  alkali  is  added  to  blood  and 
the  solution  is  boiled,  alkaline  hematin  is  produced,  and  the  solution  becomes 
olive  green  in  color.  The  absorption  band  of  the  new  compound  is  in  the 
red,  near  to  D,  and  the  blue  end  of  the  spectrum  is  absorbed  to  a  considerable 
extent.     If  a  reducing  agent  be  added,  two  bands  resembling  those  of  oxy- 


Fig.  123. — Hematoidin  Crystals.      (Frey.)  Fig.  123a. — Hemin  Crystals.      (Frey.) 

hemoglobin,  but  nearer  to  the  blue,  appear;  this  is  the  spectrum  of  reduced 
hematin,  or  hemochromogeu.  On  violently  shaking  the  reduced  hematin 
with  air  or  oxygen  the  two  bands  are  replaced  by  the  single  band  of  alkaline 
hematin. 

Hematoidin.  This  substance  is  found  in  the  form  of  yellowish  crystals, 
figure  123,  in  old  blood  extravasations  and  is  derived  from  the  hemoglobin. 
Their  crystalline  form  and  the  reaction  they  give  with  fuming  nitric  acid 
seem  to  show  them  to  be  closely  allied  to  Bilirubin,  the  chief  coloring  matter 
of  the  bile,  and  in  composition  they  are  probably  either  identical  or  isomeric 
with  it. 

Hemin.  One  of  the  most  important  derivatives  of  hematin  is  hemin. 
It  is  usually  called  Hydrochloride  of  Hematin,  but  its  exact  chemical  com- 
position is  uncertain.  Its  formula  is  said  to  be  C32H30N4FeO3HCl,  and  it 
contains  5.18  per  cent  of  chlorine,  but  by  some  it  is  looked  upon  as  simply 
crystallized  hematin.  Although  difficult  to  obtain  in  bulk,  a  specimen  may 
be  easily  made  for  the  microscope  in  the  following  way: — A  small  drop  of 
dried  blood  is  finely  powdered  with  a  few  crystals  of  common  salt  on  a  glass 
slide  and  spread  out;  a  cover-glass  is  then  placed  upon  it,  and  glacial  acetic 
acid  added  by  means  of  a  capillary  pipet.  The  blood  at  once  turns  a  brownish 
color.     The  slide  is  then  heated,  and  the  acid  mixture  evaporated  to  dryness 


12G  THE    BLOOD 

at  a  high  temperature.  The  excess  of  salt  is  washed  away  with  water  from 
the  dried  residue,  and  the  specimen  may  then  be  dried  and  mounted.  A 
large  number  of  small,  dark,  reddish  black  crystals  of  a  rhombic  shape, 
sometimes  arranged  in  bundles,  will  be  seen  if  the  slide  be  subjected  to  micro- 
scopic examination,  figure  123a. 

.The  formation  of  these  hemin  crystals  is  of  great  interest  and  importance 
from  a  medico-legal  point  of  view,  as  it  constitutes  the  most  certain  and 
delicate  test  we  have  for  the  presence  of  blood  (not  of  necessity  the  blood 
of  man)  in  a  stain  on  clothes,  etc.  It  exceeds  in  delicacy  even  the  spectro- 
scopic test.  Compounds  similar  in  composition  to  hemin,  but  containing 
hydrobromic  or  hydriodic  acid,  instead  of  hydrochloric,  may  be  also  readily 
obtained. 

Variations  in  the  Composition  of  Healthy  Blood.  The  conditions 
which  appear  most  to  influence  the  composition  of  the  blood  in  health  are 
these:  Diet,  Exercise,  Sex,  Pregnancy,  and  Age. 

Sex.  The  blood  of  men  differs  from  that  of  women,  chiefly  in  being  of 
somewhat  higher  specific  gravity,  from  its  containing  a  relatively  larger 
quantity  of  red  corpuscles. 

Pregnancy.  The  blood  of  pregnant  women  has  rather  lower  than  the 
average  specific  gravity.  The  quantity  of  the  colorless  corpuscles  is  increased 
in  the  later  months,  especially  in  primipara?;  it  is  also  claimed  that  the 
fibrin  is  increased  in  amount. 

Age.  The  blood  of  the  fetus  is  very  rich  in  solid  matter,  and  especially 
in  colored  corpuscles;  and  this  condition,  gradually  diminishing,  continues 
for  some  weeks  after  birth.  The  quantity  of  solid  matter  then  falls  during 
childhood  below  the  average,  rises  during  adult  life,  and  in  old  age  falls  again. 

Diet.  Such  differences  in  the  composition  of  the  blood  as  are  due  to  the 
temporary  presence  of  various  matters  absorbed  with  the  food  and  drink, 
as  well  as  the  more  lasting  changes  which  must  result  from  generous  or  poor 
diet  respectively,  need  be  here  only  referred  to. 

Effects  0}  Bleeding.  The  result  of  bleeding  is  to  diminish  the  specific 
gravity  of  the  blood,  and  so  quickly  that  in  a  single  venesection  the  portion 
of  blood  last  drawn  has  often  a  less  specific  gravity  than  that  of  the  blood  that 
flowed  first.  This  is,  of  course,  due  to  absorption  of  fluid  from  the  tissues 
of  the  body.  The  physiological  import  of  this  fact,  namely,  the  instant 
absorption  of  liquid  from  the  tissues,  is  the  same  as  that  of  the  intense  thirst 
which  is  so  common  after  either  loss  of  blood,  or  the  abstraction  from  it  of 
watery  fluid,  as  in  cholera,  diabetes,  and  the  like. 

For  some  little  time  after  bleeding,  the  want  of  colored  corpuscles  is  well 
marked,  but  with  this  exception:  no  considerable  alteration  seems  to  be 
produced  in  the  composition  of  the  blood  for  more  than  a  very  short  time; 
the  loss  of  the  other  constituents,  including  the  colorless  corpuscles,  being 
very  quickly  repaired.  :  .  .   1.  - , ;     1  ;    . : 


VARIATIONS     IN    THE    COMPOSITION     OF     HEALTHY     BLOOD  127 

Variations  in  Different  Parts  of  the  Body.  The  composition  of  the  blood, 
as  might  be  expected,  is  found  to  vary  in  different  parts  of  the  body.  Thus 
arterial  blood  differs  from  venous;  and  although  its  composition  and  general 
characters  are  uniform  throughout  the  whole  course  of  the  systemic  arteries, 
they  are  not  so  throughout  the  venous  system,  the  blood  contained  in  some 
veins  differing  markedly  from  that  in  others. 

Differences  between  Arterial  and  Venous  Blood.  The  differences  between 
arterial  and  venous  blood  are  these: 

Arterial  blood  is  bright  red,  from  the  fact  that  almost  all  its  hemoglobin 
is  combined  with  oxygen,  oxyhemoglobin,  while  the  purple  tint  of  venous 
blood  is  due  to  the  deoxidation  of  a  certain  quantity  of  its  oxyhemoglobin, 
and  its  consequent  reduction  to  the  purple  variety  (deoxidized,  or  purple 
hemoglobin). 

Arterial  blood  coagulates  somewhat  more  quickly. 

Arterial  blood  contains  more  oxygen  than  venous,  and  less  carbonic 
acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary  standard 
considerably.     These  are  the  Portal,  the  Hepatic,  and  the  Splenic  veins. 

Portal  Blood.  The  blood  which  the  portal  vein  conveys  to  the  liver  is 
supplied  from  two  chief  sources;  namely,  from  the  gastric  and  mesenteric 
veins,  which  contain  the  soluble  elements  of  food  absorbed  from  the  stomach 
and  intestines  during  digestion,  and  from  the  splenic  vein.  It  must,  there- 
fore, combine  the  qualities  of  the  blood  from  each  of  these  sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  according 
to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and  can  therefore 
be  seldom  exactly  the  same.  Speaking  generally,  and  without  considering 
the  sugar  and  other  soluble  matters  which  may  have  been  absorbed  from 
the  alimentary  canal,  this  blood  appears  to  be  deficient  in  solid  matters, 
especially  in  colored  corpuscles,  owing  to  dilution  by  the  quantity  of  water 
absorbed,  to  contain  an  excess  of  proteid  matter,  and  to  yield  a  less  tenacious 
kind  of  fibrin  than  that  of  blood  generally. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  two  factors, 
the  splenic  and  mesenteric  venous  blood,  is  usually  of  lower  specific  gravity 
than  blood  generally,  is  more  watery,  contains  fewer  colored  corpuscles, 
more  proteids,  and  yields  a  less  firm  clot  than  that  yielded  by  other  blood, 
owing  to  the  deficient  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of  an 
error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the  portal  vein, 
recent  observers  have  determined  that  hepatic  venous  blood  contains  less 
water,  proteids,  and  salts  than  the  blood  of  the  portal  veins;  but  that  it  yields 
a  much  larger  amount  of  extractive  matter,  in  which  is  one  constant  element, 
namely,  grape-sugar,  which  is  found,  whether  saccharine  or  farinaceous 
matter  has  been  present  in  the  food  or  not. 


128  THE     BLOOD 

GLOBULOCIDAL   AND   OTHER   PROPERTIES   OF   SERUM. 

Cytolysis.  It  has  been  known  for  some  time  that  the  sera  of  certain 
animals  when  injected  into  the  circulation  of  animals  of  another  species  will 
cause  destructive  changes  in  the  blood-corpuscles,  accompanied  by  symptoms 
of  poisoning,  which  may  even  end  fatally.  These  results  served  to  bring  into 
disrepute  the  use  of  foreign  blood  in  transfusion,  which  has  consequently 
been  practically  abandoned.  This  discharge  of  the  hemoglobin  of  the  red 
blood-corpuscles  and  solution  in  the  plasma  (laking)  is  now  included  in  the 
general  term  Cytolysis,  and  more  specifically  known  as  Hemolysis.  Agents 
which  produce  such  an  effect  are  known  as  hemolytic  or  hemotoxic  agents. 
Sera  of  one  species  are  not  hemolytic  for  blood  of  all  other  species,  but  the 
serum  of  one  animal  may  be  made  to  acquire  such  properties  for  the  blood 
of  another. 

This  adaptation  is  brought  about  in  the  following  way:  For  instance, 
the  blood  of  the  guinea-pig,  which  is  not  normally  lytic  for  the  red  cells  of  the 
rabbit,  may  be  adapted  to  the  latter  by  previously,  at  several  successive 
intervals  (three  to  seven  days)  injecting  into  the  abdominal  cavity  or  sub- 
cutaneous tissues  of  the  guinea-pig  small  quantities  of  rabbit's  blood.  If 
now  a  small  quantity  of  serum  be  obtained  from  the  guinea-pig  by  the  usual 
methods  and  mixed  in  a  test  tube  with  some  of  the  rabbit's  blood  diluted 
with  physiological  salt  solution,  hemolysis  occurs.  That  is,  the  coloring 
matter  of  the  rabbit's  red  blood-cells  goes  into  solution  and  the  cells  appear 
under  the  microscope  as  shadow  corpuscles  or  ghosts,  devoid  of  hemoglobin. 
Such  an  artificially  produced  hemolytic  serum  is  only  lytic  for  the  blood  of 
the  animal  species  for  which  it  has  been  adapted.  It  is  true  that  it  may  also 
show  slightly  lytic  properties  for  closely  allied  species.  It  has  therefore  been 
suggested  as  a  possible  valuable  aid  in  determining  relationships  of  various 
animal  species. 

Concerning  the  nature  of  the  lytic  substance,  it  has  been  found  that  it 
probably  consists  of  two  bodies  acting  conjointly,  for  if  the  serum  be  heated 
to  560  C.  for  a  short  time,  its  lytic  powers  are  lost,  but  may  be  restored  by 
adding  a  little  serum  of  another  animal  of  the  same  species  which  has  not 
been  adapted,  and  whose  serum  is  consequently  not  in  itself  lytic.  Of  these 
two  bodies,  therefore,  one  is  stable  and  is  formed  only  in  the  adapted  serum, 
while  the  other  is  more  unstable  or  labile  (destroyed  at  560  C.)  and  exists 
normally  in  the  blood  plasma.  The  former  is  known  as  the  immune  body 
and  the  latter  as  alexin.  Lysis  occurs  only  when  both  are  present  at  the  same 
time,  and  not  through  the  agency  of  one  or  the  other  singly. 

This  cytolytic  adaptation  has  been  extended  to  include  other  cells  besides 
the  red  blood-corpuscles.  Thus  in  a  similar  manner  leucolytic,  hepatolytic, 
nephrolytic,  and  a  number  of  other  lytic  sera  have  been  developed. 

It  is  further  possible,  under  certain  circumstances,  that  substances  may 


AGGLUTINATIVE     SUBSTANCES 


120 


be  developed  in  the  tissues  which  are  lytic  for  other  tissue  cells  of  the  same 
animal,  autolytic  substances.  This  may  be  an  important  physiological  process 
in  the  elimination  of  worn-out  tissue  cells,  cellular  elements  in  injury,  in- 
flammation, etc. 

Agglutinative  Substances.  A  further  property  of  adapted  sera  is 
that  of  agglutination.  The  adaptation  is  secured  in  the  same  way  as  in 
the  production  of  cytolysins.  In  fact,  both  cytolysis  and  agglutination  may 
occur  at  the  same  time.  The  normal  blood  serum  of  some  animals  may 
be  agglutinative  for  the  blood-cells  of  some  other  species.  In  normal  serum, 
agglutinative  and  cytolytic  properties  may  be  present  together  or  one  onlv 
may  be  normally  present. 

The  activity  of  agglutinative  substances  is  not  destroyed  at  a  tempera- 
ture of  560  C.  They  do  become  inert,  however,  at  700  C,  and,  furthermore, 
they  cannot  be  restored  by  adding  normal  serum,  as  is  the  case  with  cytolysins. 

Precipitins.  Other  forms  of  adaptive  substances  which  may  be 
found  in  animal  serum  are  those  which,  when  mixed  with  the  substances 
by  means  of  which  adaptation  has  been  secured,  form  a  precipitate.  Bv 
this  means  blood  of  different  species  cf  animals  may  be  detected  even  when 
in  a  dried  state.  It  has  been  suggested  as  a  possible  valuable  aid  in  medico- 
legal cases,  since  human  blood  in  a  dilution  of  1  to  50,000  has  been  recognized 
bv  this  means. 


Physical  Factors.  Diffusion,- Osmosis,  Dialysis.  The  term  diffusion  has  long  been 
applied  to  the  regular  mixing  of  the  molecules  of  two  gases  when  brought  into  contact 
in  a  confined  space,  this  interpenetration  being  due  to  the  to-and-fro  movements  of  their 
molecules.  More  recently  it  has  been  applied  to  the  mixing  of  the  molecules  of  two 
solutions  when  brought  into  contact,  as  it  has  been  found  that 
they  act  in  the  same  way  and  obey  the  same  laws  as  gases.  If, 
however,  the  two  solutions  are  separated  by  a  membrane,  perme- 
able to  the  solutions,  diffusion  will  still  occur.  To  this  form  of 
diffusion  the  term  Osmosis  has  been  applied  in  the  case  of  water, 
and  Dialysis  in  the  case  of  diffusible  substances.  All  bodies  can 
be  divided  into  two  groups,  crystalloids  and  colloids.  To  the  for- 
mer group  belong  bodies  having  a  crystalline  form,  which  readily 
go  into  solution  in  water.     All  such  bodies  are  diffusible  (dialyz- 

M 


fl 

1 

=^=^3:== 

= ~ 

gfflEHHl 

^^^^== 

==11111 

^^^^= 

j^^=j 

=EESFdS=r| 

-            ~^^          

B 


Fig.  124. 


Fig.  12s. 


130  THF.    BLOOD 

able),  their  power  of  dialysis,  however,  varying  considerably.  To  the  second  group  belong 
such  bodies  as  have  no  crystalline  form  (amorphous).  These  are  generally  bodies  with  a 
large  molecule,  which  form  colloidal  suspensions  in  water,  and  are  only  slightly  or  not  at  all 
diffusible.  An  exception  to  this  second  group  is  hemoglobin,  which  has  a  very  large  mole- 
cule but  is  crystalline  and  is  diffusible.     The  following  may  serve  as  simple  illustrations: 

Take  a  jar  and  divide  it  in  two  equal  parts  by  an  animal  membrane,  M,  figure  143, 
and  place  an  equal  amount  of  distilled  water  in  the  two  sides,  A  and  B.  Now,  since 
the  molecules  of  water  act  like  those  of  a  gas,  and  are  continually  moving  to  and  fro, 
bombarding  all  the  surfaces  of  their  retainer,  the  molecules  of  water  in  A  and  B  will  be 
continually  striking  all  the  surfaces  of  A  and  B  ;  but  since  the  membrane  is  permeable 
to  the  water  molecules,  there  will  be  a  continual  interchange  of  molecules  between  A  and 
B.  If  now,  in  one  side  A  we  place  a  solution  of  sodium  chloride,  still  keeping  water 
in  B,  the  membrane  being  permeable  to  the  sodium  chloride,  the  first  thing  we  should 
notice  would  be  an  increase  in  the  amount  of  water  in  A .  Formerly  it  would  have  been 
said  that  "  the  salt  had  attracted  the  water."  Now  we  should  say  that  the  salt  had  a  cer- 
tain osmotic  pressure.  The  salt,  however,  being  able  to  pass  (dialyze)  through  the  mem- 
brane, will  do  so,  and  this  will  continue  until  the  strength  of  the  two  salt  solutions,  and 
therefore  the  osmotic  pressure  on  both  sides,  is  equal. 

Osmotic  Pressure.  If  now  in  A  we  place  a  solution  of  some  soluble  colloidal  sub- 
stance to  which  the  membrane  is  impermeable,  or  else  replace  the  membrane,  M,  we 
used  in  our  former  experiment  by  one  which  is  not  permeable  to  the  sodium  chloride,  and 
arrange  our  jar  as  in  figure  125,  so  as  to  be  able  to  read  off  any  increase  of  water  which  may 
pass  into  A ,  we  will  notice  that  the  amount  of  liquid  in  A  will  continue  to  increase  up  to  a 
certain  point.  Once  that  point  is  reached,  there  will  be  no  further  change,  since  the  sub- 
stance in  solution,  in  A,  cannot  pass  through  the  membrane  as  in  the  previous  example. 
This  pressure  can  be  measured  and  expressed  in  millimeters  of  mercury.  It  is  constant  for 
all  solutions  of  this  substance  that  are  of  the  same  concentration  when  measured  under  like 
conditions  of  temperature  and  pressure,  and  is  called  the  Osmotic  pressure  of  this  solution. 

Of  the  numerous  explanations  regarding  the  nature  of  osmotic  pressure  which  have 
been  more  or  less  satisfactory,  a  simple  one,  and  one  that  can  be  easily  understood,  is  as 
follows:  In  figure  125  one  surface  of  the  membrane  is  being  bombarded  by  the  molecules 
of  a  non-diffusible  substance  mixed  with  those  of  a  diffusible  one  (water) ;  while  the  other 
surface  is  being  bombarded  entirely  by  water  molecules.  The  former  condition  per- 
mits less  water  to  diffuse  out,  since  fewer  molecules  get  to  the  surface  of  the  membrane; 
while  the  latter  permits  all  of  the  molecules  which  reach  it  to  pass  through. 

Osmotic  pressure  can  be  estimated  in  several  different  ways  in  addition  to  the  above, 
viz.,  the  determination  of  the  freezing  point  of  the  solution,  determination  of  the  boiling 
point,  determination  of  the  electrical  conductivity.  The  results  obtained  with  the  various 
methods  agree  very  closely.  The  following  solutions  have  the  same  osmotic  pressure: 
Sodium  chloride,  0.64  per  cent;   potassium  nitrate,  1.09  per  cent;   sugar  5.5  per  cent. 

Isotonic  Solutions.  Solutions  that  have  the  same  osmotic  pressure  are  called  iso- 
tonic. The  term  isotonic  is  a  relative  one,  implying  a  comparison  with  some  other  solu- 
tion taken  as  a  standard.  In  physiology  it  has  been  customary  to  take  blood-plasma 
as  a  standard.  A  solution  of  0.64  per  cent  sodium  chloride  is  isotonic  for  the  blood-plasma 
of  the  frog,  and  a  0.9  per  cent  solution  for  that  of  man.  Further,  any  solution  which  is 
of  a  lower  osmotic  pressure  than  the  standard  solution  is  said  to  be  hypoisotonic  (hypotonic) 
in  relation  to  that  solution.  A  solution  of  a  higher  osmotic  pressure  is  said  to  be  hyper- 
isotomc  (hypertonic). 

Water  passes  in  the  Direction  of  the  Arrows. 
Hypertonic  saline  solution (2  per  cent) 

i 

Blood -plasma 

ri 

Isotonic  saline  solution (0.64  per  cent) 

I 
Hypotonic  saline  solution (0.3    per   cent) 


THE    CHARACTER    AND     COMPOSITION    OF    LYMPH  131 

If  a  hypotonic  solution  be  mixed  with  blood,  water  from  the  hypotonic  solution  passes 
through  the  cell  membrane  of  the  red  corpuscles  into  the  stroma,  and  causes  it  to  swell. 
The  hemoglobin  at  the  same  time  passes  out  and  goes  into  solution  in  the  diluted  plasma. 
On  the  other  hand,  the  addition  of  a  hypertonic  solution  to  the  plasma  causes  the  red  cor- 
puscles to  lose  their  water  and  become  crenated.  The  principles  of  osmosis  have  been 
derived  from  the  action  of  substances  separated  by  dead  animal  or  plant  membranes.  It 
must  be,  however,  remembered  that  in  the  application  of  these  principles  to  processes 
occurring  in  the  living  organism,  the  cells,  forming  the  various  membranes,  are  an  im- 
portant modifying  factor.  It  is  probable  that  physico-chemical  processes,  occurring  in 
the  protoplasm  the  cell,  may  change  its  permeability  to  the  same  substance  at  different 
times. 

THE  CHARACTER  AND  COMPOSITION  OF  LYMPH. 

The  lymph  is  the  fluid  which  immediately  surrounds  the  tissue  cells  of 
the  living  body.  It  fills  up  the  spaces  between  the  cells  themselves  and 
between  the  cells  and  the  blood-vessels  which  ramify  among  the  cell-masses. 
The  lymph,  therefore,  is  an  intermediate  fluid  between  blood-plasma  on  the 
one  hand,  and  the  tissue  cells  on  the  other,  receiving  its  ingredients  by  the 
passage  of  fluid  from  the  plasma  through  the  walls  of  the  finer  blood-vessels 
in  the  one  direction,  and  by  the  discharge  of  the  substances  from  the  cells 
themselves  in  the  other. 

The  Chemical  Composition  of  the  Lymph.  Since  the  chief  source 
of  the  lymph  is  the  blood-plasma,  one  would  naturally  expect  that  its  chemical 
composition  would  be  very  similar  to  that  of  plasma,  which  is  in  fact  the  case. 
The  variations  that  are  noted  in  lymph  taken  from  definite  sources  no  doubt 
have  their  origin  in  the  fact  that  the  lymph  passes  through  these  organs  slowly, 
and  that  ingredients  peculiar  to  the  necessities  of  the  function  and  growth 
of  the  differentiated  tissue  of  the  organ  are  taken  from  the  lymph  in  special 
organs.  Lymph  obtained  from  a  human  lymphatic  fistula  has  been  analyzed; 
the  figures  from  Hammarsten  are  as  follows,  though  considerable  variations 
appear  in  the  analyses  from  other  authorities: 

ANALYSIS    OF    LYMPH. 

Per  cent 

Water 94.5     to  96.5 

Solids 3.7     to     5.5 

Albumins 3.4     to     4.1 

Ethereal  extract 0.06  to     0.13 

Sugar 0.1 

Salts 0.8     to     0.9 

Sodium  chloride 0.55  to     0.58 

Sodium  carbonate 0.24 

Disodic  phosphate 0.028 

The  most  notable  fact  to  be  derived  from  this  composition  table  is  the 
low  percentage  of  proteids  present  in  the  lymph. 

The  Formation  of  Lymph.  The  manner  in  which  the  substances 
in  the  lymph  pass  through  the  walls  of  the  capillaries  from  the  plasma  is  a 


132  THE     BLOOD 

question  which  has  been  surrounded  with  considerable  difficulty.  It  is 
thought  by  Ludwig  and  many  of  his  followers  that  the  process  involved 
is  merely  one  of  filtration.  Certainly  the  blood  pressure  in  the  capillaries 
is  in  the  main  greater  than  that  of  the  pressure  of  the  lymph  in  the  surround- 
ing tissues,  and  this  positive  pressure  will  contribute  so  much  to  the  direct 
ingredients  of  the  blood-plasma  through  the  capillary  walls.  It  is  true,  as  a 
matter  of  experiment,  that  anything  which  contributes  to  an  increase  in  the 
capillary  pressure  is  very  apt  to  produce  an  edema  of  the  corresponding 
tissues.  Since  the  colloidal  materials  represented  by  the  proteid  are  non- 
diffusible,  one  would  by  this  theory  expect  to  find  a  diminished  percentage 
in  the  lymph,  which  is  true,  though  not  to  the  extent  which  the  theory  demands. 

Heidenhain  was  the  first  to  question  the  adequacy  of  the  blood 
pressure  and  filtration  hypothesis.  He  showed  that  many  of  the  conditions 
under  which  lymph  formation  takes  place  are  not  sufficient  to  produce  nitra- 
tions of  the  material  found.  He  advanced  the  hypothesis  that  the  living 
endothelial  lining  of  the  blood-vessels  exerted  a  secretory  activity  in  lymph 
production.  He  discovered  that  various  substances  known  as  lymphagogues 
when  introduced  into  the  circulatory  system  produce  a  remarkable  increase 
in  the  flow  of  lymph  from  the  thoracic  duct.  Further,  he  noticed  that  the 
concentration  of  the  lymph  was  changed,  i.e.,  increased.  It  has  been  sug- 
gested that  these  substances  act  to  change  the  normal  resistance  of  the  endo- 
thelial cells,  and  this  has  been  offered  as  a  criticism.  Nevertheless  man}' 
drugs  act  to  increase  the  flow  of  lymph  in  a  way  which  cannot  be  presumed 
to  be  other  than  normal,  i.e.,  they  stimulate  the  physiological  processes  going 
on  in  the  endothelial  cells.  Such  observations  contribute  strongly  to  the 
view  advanced  by  Heidenhain.  Many  investigations  have  been  brought  to 
the  support  of  the  hypothesis  that  lymph  formation  is  largely  a  process  of 
secretion,  yet  it  seems  at  the  present  time  that  we  cannot  wholly  deny  that 
filtration  and  osmosis  play  a  part  in  the  processes.  Certainly  the  permea- 
bility or  activity  of  the  endothelial  lining  of  the  blood-vessels  varies  greatly 
at  different  times  in  the  life  of  an  individual,  and  this  variation  in  function  is 
associated  with  the  marked  change  in  the  character  and  quantity  of  lymph 
produced. 

The  second  factor  in  lymph  formation,  the  activity  of  the  tissue  in  taking 
up  or  discharging  materials  into  the  lymph-mass,  must  not  be  ignored  alto- 
gether. 

LABORATORY  EXPERIMENTS  FOR  THE  EXAMINATION  OF 

THE  BLOOD. 

i.  Microscopical  Examination  of  the  Blood.  Mount  a  drop  of  frog's 
blood  in  0.7  per  cent  sodium  chloride  and  examine  with  the  low  power  of  a 
compound  microscope.     The  red  corpuscles  will  appear  as  oval  nucleated 


ACTION    OF    FLUIDS    ON    THE    RED     CORPUSCLES  133 

discs  with  a  faint  yellowish  color,  figure  no.  Here  and  there  white  granular 
cells  of  irregular  outline  will  be  noted,  the  white  corpuscles.  Examine  the 
drop  of  blood  with  a  high  magnifying  power  and  sketch  the  outline  of  the 
blood  cells.  Select  the  white  corpuscle  -which  is  most  irregular  in  outline 
and  make  a  series  of  outline  drawings  once  every  minute  to  show  its  ame- 
boid movements,  figure  117. 

Draw  a  drop  of  your  own  blood  by  puncturing  the  tip  of  the  finger,  under 
sterile  conditions,  and  mount  in  a  drop  of  0.9  per  cent  physiological  saline. 
Examine  with  a  high  power,  note  the  small  biconcave  red  corpuscles  which 
appear  faintly  yellow  in  color  and  even  adhere  in  rouleaux,  figure  109.  The 
white  corpuscles  will  appear  as  somewhat  larger  granular  discs  differing  in 
form  and  size.  By  mounting  a  drop  of  blood  on  a  warm  stage  the  ameboid 
movements  of  the  white  corpuscles  can  be  observed  with  comparative  ease. 

2.  Action  of  Fluids  on  the  Red  Corpuscles.  Water.  When  water  is 
added  gradually  to  frog's  blood,  the  oval  disc-shaped  corpuscles  become 
spherical  and  gradually  discharge  their  hemoglobin,  a  pale,  transparent 
stroma  being  left  behind.     Human  red  blood  cells  change  from  a  discoidal 

O 


Fig.  126.  Fig.  127.  Fig.  128.  Fig.  129. 

Fig.  126. — Effect  of  Hypertonic  Salt-Solution  on  the  Red  Blood-Corpuscles  of  Man. 
Fig.  127.— Effect  of  Acetic  Acid.     Fig.  128. — Effect  of  Tannin.     Fig.  129. — Effect  of  Boric  Acid. 

to  a  spheroidal  form  and  discharge  their  cell-contents,  becoming  quite  trans- 
parent and  all  but  invisible  (ghost  corpuscles). 

Hypertonic  Salt-Solutions.  Mount  a  drop  of  human  blood  in  2  per  cent 
sodium-chloride  solution.  The  red  blood  cells  lose  their  disc  shape  and  be- 
come spherical  with  spinous  projections  or  crenations,  figure  126. 

The  original  form  of  the  red  blood  cells  can  be  restored  by  transferring 
them  to  isotonic  salt-solution. 

Dilute  Acetic  Acid.  This  reagent  causes  the  nucleus  of  the  red  blood 
cells  in  the  frog  to  become  more  clearly  defined;  if  the  action  is  prolonged, 
the  nucleus  becomes  strongly  granulated,  and  all  the  coloring  matter  seems 
to  be  concentrated  in  it,  the  surrounding  cell-substance  and  outline  of  the 
cell  becoming  almost  invisible;  after  a  time  the  cells  lose  their  color  altogether. 
The  cells  in  figure  127  represent  the  successive  stages  of  the  change.  A 
similar  loss  of  color  occurs  in  the  red  cells  of  human  blood,  which,  from  the 
absence  of  nuclei,  seem  to  disappear  entirely. 

Alkalies.  Alkalies  cause  the  red  blood-corpuscles  to  absorb  water  and 
finally  to  disintegrate. 


134  THE     BLOOD 

Chloroform  and  Ether.  These  reagents  when  added  to  the  red  blood 
cells  of  the  frog  cause  them  to  part  with  their  hemoglobin;  the  stroma  of  the 
cells  becomes  gradually  broken  up.  A  similar  effect  is  produced  on  the  human 
red  blood  cell. 

Tannin  and  Boric  Acid.  When  a  2  per  cent  fresh  solution  of  tannic  acid 
is  applied  to  frog's  blood  it  causes  the  appearance  of  a  sharply  defined  little 
knob,  projecting  from  the  free  surface  (Roberts'  macula).  The  coloring 
matter  becomes  at  the  same  time  concentrated  in  the  nucleus,  which  grows 
more  distinct,  figure  128.  A  somewhat  similar  effect  is  produced  on  the 
human  red  blood-corpuscle. 

A  2  per  cent  solution  of  boric  acid  applied  to  nucleated  red  blood  cells 
of  the  frog  will  cause  the  concentration  of  all  the  coloring  matter  in  the  nucleus; 
the  colored  body  thus  formed  gradually  quits  its  central  position,  and  comes 
to  be  partly,  sometimes  entirely,  protruded  from  the  surface  of  the  now 
colorless  cell,  figure  129.  The  result  of  this  experiment  led  Briicke  to  dis- 
tinguish the  colored  contents  of  the  cell  (zobid)  from  its  colorless  stroma 
(ecoid).  When  applied  to  the  non-nucleated  mammalian  corpuscle  its  effect 
merely  resembles  that  of  other  dilute  acids. 

3.  Phagocytosis  in  White  Corpuscles.  Mix  some  very  fine  pigment 
granules,  powdered  vermilion,  or  charcoal  with  a  few  drops  of  frog's  blood, 
let  stand  for  10  or  20  minutes,  then  mount  a  drop  on  the  glass  slide  and  ex- 
amine under  a  high-magnifying  microscope.  In  a  favorable  field  here  and 
there  will  be  found  some  white  corpuscles  which  have  taken  up  the  pigment. 
Colored  corpuscles  have  been  observed  with  fragments  of  pigment  embedded 
in  their  substance.  White  corpuscles  have  also  been  seen  in  diseased  states 
of  the  body  to  contain  micro-organisms,  for  example,  bacilli,  and  are  said  to  have 
the  power  of  destroying  these  organisms,  which  gives  them  the  name  phagocytes. 

4.  Enumeration  of  the  Blood-Corpuscles.  Several  methods  are 
employed  for  counting  the  blood-corpuscles,  most  of  them  depending  upon 


Fig.  130. — Thoma-Zeiss  Hemacytometer,  glass  slide. 

the  same  principle,  i.e.,  the  dilution  of  a  minute  volume  of  blood  with  a 
given  volume  of  a  colorless  solution  similar  in  specific  gravity  to  blood-plasma, 
so  that  the  size  and  shape  of  the  corpuscles  are  altered  as  little  as  possible. 
A  minute  quantity  of  the  well-mixed  solution  is  then  taken,  examined  under 
the  microscope,  either  in  a  flattened  capillary  tube  (Malassez)  or  in  a  cell 
(Hayem  and  Nachet,  Gowers)  of  known  capacity,  and  the  number  of  corpus- 
cles in  a  measured  length  of  the  tube,  or  in  a  given  area  of  the  cell,  is  counted. 
The  length  of  the  tube  and  the  area  of  the  cell  are  ascertained  by  means  of 
a  micrometer  scale  in  the  microscope  ocular;  or  in  the  case  of  Gowers'  modi- 


THE  PERCENTAGE  OF  CORPUSCLES  AND  PLASMA 


135 


fication,  by  the  division  of  the  cell  area  into  squares  of  known  size.  Having 
ascertained  the  number  of  corpuscles  in  the  diluted  blood,  it  is  easy  to  find 
out  the  number  in  a  given  volume  of  normal  blood. 

The  hemacytometer,  which  is  most  used  at  the  present  time,  is  known  as 
the  Thoma-Zeiss  hemacytometer.  It  consists  of  a  carefully  graduated 
pipet,  in  which  the  dilution  of  the  blood  is  done;  this 
is  so  formed  that  the  capillary  stem  has  a  capacity 
equalling  one-hundredth  of  the  bulb  above  it.  If  the 
blood  is  drawn  up  in  the  capillary  tube  to  the  line  marked 
i,  figure  131,  the  saline  solution  may  afterward  be 
drawn  up  the  stem  to  the  line  101;  in  this  way  we  have 
101  parts  of  which  the  blood  forms  1.  As  the  content 
of  the  stem  can  be  displaced  unmixed  we  shall  have  in 
the  mixture  the  proper  dilution.  The  blood  and  the 
saline  solution  are  well  mixed  by  shaking  the  pipet,  in 
the  bulb  of  which  is  contained  a  small  glass  bead  for 
the  purpose  of  aiding  the  mixing.  The  other  part  of 
the  instrument  consists  of  a  glass  slide,  figure  130,  upon 
which  is  mounted  a  covered  disc,  m,  accurately  ruled 
so  as  to  present  one  square  millimeter  divided  into  400 
squares  of  one-twentieth  of  a  millimeter  each.  The 
micrometer  thus  made  is  surrounded  by  another  annu- 
lar cell,  r,  which  has  such  a  height  as  to  make  the  cell 
project  exactly  one-tenth  millimeter  beyond  m.  If  a 
drop  of  the  diluted  blood  be  placed  upon  m,  and  c  be 
covered  with  a  perfectly  flat  cover-glass,  the  volume  of 
the  diluted  blood  above  each  of  the  squares  of  the  mi- 
crometer, i.e.,  above  each  4^~o,  will  be  4-0*0 0  of  a  cubic 
millimeter.  An  average  of  ten  or  more  squares  is  then  taken,  and  this  num- 
ber multiplied  by  4000X100  gives  the  number  of  corpuscles  in  a  cubic 
millimeter  of  undiluted  blood.  A  separate  pipet  is  used  for  making  dilu- 
tions for  counts  of  leucocytes.  In  this,  the  dilution  is  made  of  one  part  of 
blood  and  ten  parts  of  diluting  fluid.  Acetic  acid,  0.2  of  one  per  cent,  is 
usually  employed  for  this  purpose. 

5.  The  Percentage  of  Corpuscles  and  Plasma  in  Human  Blood. 
Fill  the  two  graduated  capillary  tubes  of  a  hematocrite  with  blood  drawn 
from  the  tip  of  your  own  finger,  insert  into  the  instrument,  and  centrifuge  as 
rapidly  as  possible.  The  experiment  must  be  performed  within  the  time 
limit  of  clotting  in  order  to  be  successful.  The  corpuscles  will  be  thrown 
down  and  the  percentage  of  plasma  and  corpuscles  can  be  read  off  directly. 
Should  one  fail  to  fill  the  tube  exactly  full,  then  the  percentage  of  plasma  and 
corpuscles  can  be  calculated  from  the  proportion  which  each  bears  to  the 
quantity  in  the  tube. 


Fig.  131. —  Thoma- 
Zeiss  Hemacytometer, 
pipet. 


136  THE     BLOOD 

6.  Estimation  of  the  Percentage  of  Hemoglobin.  The  per  cent  of 
hemoglobin  in  a  sample  of  blood  can  be  obtained  by  the  instrument  known 
as  Fleischl's  hemometer,  see  figure  122.  The  principle  of  this  instrument 
rests  on  a  comparison  of  the  color  of  the  sample  of  dilute  blood  with  a  stand- 
ard glass  wedge  of  uniform  tint  similar  to  that  of  blood.  Fill  one  of  the 
chambers  in  the  cells  of  the  instrument  half  full  with  a  2  per  cent  solution  of 
sodium  carbonate.  Now  draw  a  drop  of  blood  from  the  tip  of  a  finger. 
Touch  the  drop  with  the  end  of  the  standardized  capillary  tube,  using  care 
to  fill  it  accurately.  Quickly  wash  this  sample  of  blood  out  in  the  carbonate 
solution  in  the  cell  and  finish  filling  the  cell.  Put  distilled  water  in  the  other 
half  of  the  cell,  mount  in  the  instrument,  and  examine  in  a  dark  room,  using 
candle-light.  The  glass  wedge  is  graduated  in  percentage  which  can  be 
read  off  directly.  This  instrument  is  usually  provided  with  several  cells,  in 
which  case  as  many  samples  may  be  taken  and  the  average  of  the  readings 
used  to  determine  the  percentage. 

Perhaps  a  more  convenient  and  certainly  a  quicker  method  for  deter- 
mining the  percentage  of  hemoglobin  is  Talquist's  hemoglobinometer.  By 
this  method  a  drop  of  blood  is  drawn  directly  on  to  absorbent  paper  furnished 
with  the  instrument,  and  the  resulting  stain  is  compared  directly  with  a  paper 
color  scale  which  is  graduated  in  percentage.  In  this  method  the  comparison 
is  made  in  ordinary  daylight,  and  because  of  its  rapidity  it  is  very  convenient 
for  clinical  examinations. 

7.  Reaction  of  Blood-Plasma.  Wet  a  piece  of  neutral  litmus 
paper  (some  prefer  glazed  paper),  then  touch  one  end  of  the  strip  with  a 

,drop  of  blood  drawn  from  your  finger  under  sterile  conditions.  After  a  few 
moments  wash  off  the  excess  of  corpuscles  in  neutral  distilled  water.  The 
deeper  blue  at  the  point  of  contact  with  the  blood  indicates  alkalinity. 

8.  The  Specific  Gravity  of  Blood.  From  standard  mixtures  of 
chloroform  and  benzol  with  specific  gravity  of  1.050,  1.060,  and  1.070  make 
up  a  set  of  specific-gravity  solutions  of  1.050,  1.052,  1.054,  etc.,  to  1.070. 
These  standards  may  be  kept  in  stoppered  4-dram  vials,  or  in  test  tubes. 
The  specific  gravity  of  blood  is  determined  by  inserting  with  a  pipet 
a  drop  of  freshly  drawn  blood  into  the  middle  of  one  of  the  solutions,  say 
1.056.  Since  the  blood  does  not  mix  with  the  chloroform  and  benzol  the 
drop  will  rise  or  sink  according  to  its  relative  specific  gravity.  By  a  few 
trials  one  may  quickly  find  a  specific  gravity  in  which  the  drop  of  blood 
floats  without  rising  or  sinking.  This  represents  the  specific  gravity  of  the 
drop  of  blood. 

This  method  permits  rapid  clinical  application  and  has  proven  of  con- 
siderable interest  in  the  hands  of  clinists. 

9.  The  Isotonicity  of  Blood.  The  absorption  or  loss  of  water 
by  the  corpuscles  of  blood  in  solutions  of  other  concentrations  than  that  of 
blood-plasma  can  be  used  as  a  means  of  determining  the  isotonicity  of  blood. 


\ 


COAGULATION     OF     BLOOD 


137 


Make  up  a  series  of  solutions  of  sodium  chloride,  varying  by  tenths,  from 
0.5  to  1.2  per  cent.  Prepare  a  series  of  slides  with  vaseline  rings  and  mount 
drops  of  human  blood  in  drops  of  saline  of  0.6,  0.7,  0.8,  0.9,  1,  and  1.1  per 
cent,  examine  every  ten  minutes  under  a  high-power  microscope.  The 
corpuscles  of  some  of  the  slides  will  swell  up  and  may  disintegrate,  others 
will  show  crenation  as  in  figure  126.  In  the  isotonic  solutions  the  corpus- 
cles will  appear  of  their  normal  size  and  condition. 

10.  Coagulation  of  Blood,  a.  Normal  Clot.  Anesthetize  a  dog, 
insert  a  cannula  into  the  carotid  or  femoral  artery,  and  draw  samples  of 
blood  into  two  or  three  clean,  dry  test  tubes.  Draw  one  sample  into  a  test 
tube  that  has  had  its  sides  oiled.  Note  the  exact  time  at  which  the  blood 
was  drawn  into  the  test  tubes  and  set  the  test  tubes  in  a  test-tube  rack.  Ex- 
amine at  intervals  of  30  seconds  by  gently  inclining  the  test  tubes.     Presently 


Fig.  132. — Miscroscopic  View  of  Clot  Showing  Fibrin  Network. 

it  will  be  noted  that  the  blood  becomes  more  viscous  and  does  not  flow  freely 
up  the  sides  of  the  test  tubes.  Later  the  whole  mass  will  become  jelly-like 
and  will  retain  the  form  of  the  test  tube.  Note  the  time  of  the  first  slight 
change,  and  also  when  the  clot  becomes  more  perfect.  The  sample  in  the 
oiled  test  tube  will  be  found  to  clot  more  slowly. 

If  the  test  tubes  of  clotted  blood  are  left  standing  for  a  day,  the  coagulum 
will  become  similar  in  size  and  a  transparent  yellowish  blood  will  make  its 
appearance  on  the  surface  or  between  the  sides  of  the  clot  and  the  test-tube 
wall.  This  fluid  is  the  serum  and  it  is  squeezed  out  by  the  shrinking  of  the 
fibrin  which  holds  the  corpuscles  in  its  meshes. 

b.  Microscopic  Examination  oj  the  Process  0}  Clotting.     Take  a  drop  of 


138  THE     BLOOD 

fresh  blood  from  the  tip  of  your  finger  under  sterile  conditions  and  mount 
on  a  microscopic  slide  in  a  few  drops  of  salt-solution,  and  examine  immediately 
under  the  high  power.  Small  threads  of  fibrin  will  presently  be  seen  to 
form  across  the  field,  usually  being  most  clearly  obvious  where  fragments 
of  white  corpuscles  are  noted,  see  figures  107  and  132.  The  threads  of 
fibrin  become  more  apparent  when  stained  with  rosanilin. 

c.  Whipped  Blood.  Draw  a  sample  of  blood  into  a  glass  tumbler, 
enough  to  fill  it  one-half  or  two-thirds  full.  Immediately  begin  vigorously 
stirring  the  blood  with  a  bunch  of  stiff  wires  or  a  pencil,  and  keep  it  up  until 
the  time  of  clotting  has  passed,  5  or  10  minutes.  In  this  instance  the  wires 
will  break  up  and  collect  the  fibrin  as  fast  as  it  forms,  and  no  firm  mass  will 
be  produced.  The  remaining  fluid  is  called  whipped  blood.  The  fibrin  can 
be  removed  from  the  wires  and  washed  in  tap  water  until  all  the  adherent 
red  corpuscles  are  removed.  This  mass  of  fibrin  is  white,  elastic,  and  com- 
posed of  a  network  of  thread-like  fibers.  It  is  these  fibers  extending  through 
and  through  the  mass  of  blood  which  makes  it  retain  the  form  of  the  vessel 
when  undisturbed  clotting  occurs. 

d.  The  Influence  oj  Salt-Solution  on  Blood-Clotting.  Add  20  c.c.  of  satu- 
rated magnesium  sulphate,  1  per  cent  sodium  oxalate,  and  2.5  per  cent  of 
sodium  chloride  in  each  of  3  beakers.  Draw  into  each  beaker  50  to  60  c.c.  of 
blood  and  immediately  mix  thoroughly  and  let  stand.  The  magnesium  and 
oxalate  beakers  will  not  coagulate  even  though  they  stand  for  days,  but  the 
sodium-chloride  blood  will  clot  in  a  few  minutes. 

The  magnesium-sulphate  blood  will  coagulate  if  diluted  with  a  sufficient 
amount  of  distilled  water  or  physiological  saline  solution.  Make  a  series 
of  dilutions  and  note  when  coagulation  takes  place.  The  sodium-oxalate 
blood  will  coagulate  when  a  sufficient  excess  (1  per  cent)  of  calcium  chloride 
is  added  to  neutralize  the  excess  of  sodium  oxalate.  Demonstrate  this  on 
a  series  of  samples. 

If  a  liter  or  so  of  magnesium  or  oxalate  blood  is  secured  and  separated 
by  a  centrifuge,  or  by  leaving  stand  for  a  sufficient  time,  a  sample  of  salted 
plasma  will  be  obtained.  This  sample  will  coagulate  when  it  is  treated  as 
just  described  for  salted  blood,  showing  that  the  antecedents  of  fibrin  are 
found  in  the  plasma. 

e.  Action  oj  Tissue  Extracts  on  Coagulation.  Wash  out  the  blood  of 
a  small  animal  by  circulating  0.9  per  cent  saline  through  the  arteries  until 
the  outflowing  fluid  from  the  veins  is  clear.  Take  an  organ,  the  liver  for 
example,  grind  it  up  in  a  sausage  mill  by  running  it  through  the  mill  two 
or  three  times,  then  extract  with  0.9  per  cent  physiological  saline.  The 
macerating  mass  should  be  shaken  up  at  intervals,  and  may  be  kept  from 
spoiling  by  adding  an  excess  of  chloroform  or  by  keeping  on  ice.  A  few 
cubic  centimeters  of  this  fluid  extract  added  to  a  sample  of  freshly  drawn 
blood  will  very  greatly  hasten  the  rapidity  of  coagulation.     This  tissue  ex- 


THE    CHEMISTRY    OF    BLOOD-PLASMA  139 

tract  is  called  thrombokinase,  as  it  is  an  activator  which  hastens  the  formation 
of  thrombin  from  thrombogen. 

ii.  The  Chemistry  of  Blood-Plasma  (or  Serum).  The  blood- 
plasma  contains  all  the  chemical  substances  which  are  utilized  by  the 
tissues  in  their  nutrition  or  which  are  thrown  off  by  the  tissues  as  a  re- 
sult of  their  activity.  It  is  therefore  a  very  complex  mixture.  The  serum 
contains  the  same  substances  in  the  same  proportion,  with  the  exception  of 
the  antecedents  of  fibrin.  It  may,  therefore,  be  used  as  a  substitute  for 
plasma  in  most  cases. 

a.  Proteids  of  Plasma.  There  are  three  principal  proteids  in  blood- 
plasma:  serum-albumin,  serum-globulin,  and  fibrinogen.  These  may  be 
isolated  as  follows:  To  a  sample  of  blood-plasma  add  an  equal  quantity  of 
sodium-chloride  solution  that  has  been  saturated  at  400  C.  A  white  floccu- 
lent  precipitate  of  fibrinogen  comes  down.  Filter  off,  and  add  to  the  filtrate 
an  equal  volume  of  saturated  ammonium  sulphate.  A  second  heavier  pre- 
cipitate of  serum- globulin  separates  out.  When  this  is  separated,  and  crys- 
tals of  ammonium  sulphate  are  added  to  the  filtrate  to  complete  saturation 
at  400  C,  a  third  precipitate  of  serum-albumin  separates. 

Each  of  these  precipitates  may  be  redissolved  and  purified  by  reprecipi- 
tation  and  can  be  tested  by  the  characteristic  proteid  reactions,  see  page  96, 
which  they  all  give. 

b.  Sugars  0}  Blood-Plasma  or  Serum.  If  a  quantity  of  blood-serum  is 
diluted  with  about  5  to  10  times  its  volume  of  water,  and  the  proteids  are 
removed  by  slight  acidulation  with  acetic  acid  and  boiling  and  filtering,  the 
filtrate  will  contain  reducing  sugar  and  the  various  solids  of  blood-plasma. 
To  a  concentrated  sample  of  the  filtrate  add  Fehling's  solution  and  boil. 
A  reddish  precipitate  indicates  the  presence  of  reducing  sugar.  If  this  ex- 
periment is  done  quantitatively,  about  from  0.1  to  0.2  per  cent  of  sugar  will 
be  found. 

c.  The  Salts  of  Blood-Plasma.  The  salts  of  blood-plasma  are  tested 
best  by  evaporating  some  of  the  blood  serum  to  dryness,  and  burning  the 
residue  to  oxidize  the  organic  matter  and  dissolving  the  ash  in  water.  Test 
as  follows:  To  a  sample  add  1  per  cent  of  silver  nitrate;  a  white  precipitate 
soluble  in  an  excess  of  ammonia,  but  not  soluble  in  nitric  acid,  indicates 
chlorides. 

To  a  second  sample  add  1  per  cent  barium  chloride.  If  sulphates  are 
present  there  will  be  a  white  precipitate  which  settles  out  quickly. 

Acidify  a  third  sample  with  nitric  acid  and  add  ammonium  molybdate 
and  heat.     A  yellow  precipitate  indicates  the  presence  of  phosphates. 

To  the  fourth  sample  add  an  excess  of  strong  ammonia  and  1  per  cent 
ammonium  oxalate,  heat.  A  white  precipitate  indicates  the  presence  of 
calcium. 

12.  Blood-Corpuscles.    The  characteristic  substance  in  the  composi- 


140  THE     BLOOD 

tion  of  the  corpuscles  is  the  pigment  known  as  hemoglobin,  and  this  is  the 
only  chemical  factor  that  will  be  considered  in  these  experiments. 

a.  Hemoglobin  Crystals.  Take  a  sample  of  dog's  blood,  or  if  a  centri- 
fuge is  available  separate  and  wash  the  sample  of  blood-corpuscles,  and 
mix  with  about  three  volumes  of  saturated  ether  water,  or  if  blood  is  used  dilute 
with  two  or  three  volumes  of  water  and  add  about  10  percent  of  pure  ether 
and  shake  thoroughly.  Crystals  of  oxyhemoglobin  will  be  formed,  and  this 
can  be  mounted  and  examined  with  a  microscope. 

b.  Spectrum  of  Hemoglobin  and  its  Compounds. 

i.  Oxyhemoglobin.  Dilute  a  sample  of  defibrinated  blood  with  about 
ten  volumes  of  distilled  water.  From  this  stock  solution  make  five  solutions 
all  differing  by  33%  per  cent.  Examine  these  with  a  direct-vision  spectroscope. 
Make  a  drawing  showing  the  absorption  spectrum  of  each  sample  as  com- 
pared with  the  solar  spectrum.  Compare  with  the  spectrum  shown  in  the 
frontispiece. 

2.  Hemoglobin.  The  oxygen  can  be  driven  out  from  the  hemoglobin 
by  adding  to  the  above  samples  a  few  drops  of  ammonium  sulphide  and 
gently  warming.  Re-examine  with  the  direct- vision  spectroscope  and  map 
as  before. 

3.  Carbon-Monoxide  Hemoglobin.  Pass  a  stream  of  ordinary  illumi- 
nating gas  through  the  dilutions  of  hemoglobin.  The  carbon  monoxide 
of  the  gas  will  form  a  compound  with  the  hemoglobin,  which  now  turns  a 
bright  scarlet  color.  When  examined  with  the  spectroscope,  the  absorp- 
tion bands  are  found  to  be  very  similar  to  those  of  oxyhemoglobin.  How- 
ever, map  the  spectrum  to  the  scale  as  usual.  Add  the  reducing  agent, 
warm,  and  shake  vigorously  and  re-examine.  It  is  very  difficult  to  break  up 
the  combination  of  hemoglobin  with  carbon  monoxide,  hence  the  poisonous 
action  of  this  gas. 


CHAPTER  V 

THE    CIRCULATION    OF    THE    BLOOD 


The  blood  is  contained  in  a  system  of  closed  vessels  through  which  it  is 
kept  in  circulation  during  the  life  of  an  individual.  The  energy  to  keep  up 
this  motion  is  supplied  by  the  heart,  which  is  a  large  muscular  organ  con- 
sisting of  four  great  divisions,  the  right  and  left  auricles  and  right  and  left 
ventricles.     The  right  ventricle  discharges  its  blood  into  the  pulmonary  artery, 


Fig.  133. — Diagram  of  the  Circulation  in  an  Animal  with  a  Completely  Separated  Right 
and  Left  Ventricle  and  a  Double  Circulation.  (After  Huxley.)  Ad,  Right  auricle  receiving  the 
superior  and  inferior  vena?  cava,  Vcs  and  Vci;  Dth,  thoracic  duct,  the  main  trunk  of  the  lymphatic 
system;  Ad,  right  auricle;  Vd,  right  ventricle;  Ap,  pulmonary  artery;  P,  lung;  Vp,  pulmonary 
vein;  As,  left  auricle;  Vs,  left  ventricle;  Ao,  aorta;  D,  intestine;  L,  liver;  Vp,  portal  vein;  Lv, 
hepatic  vein. 

through  which  it  passes  to  the  lungs,  returning  through  the  pulmonary  veins  to 
the  left  auricle,  and  into  the  ventricle.  From  the  left  ventricle  the  blood  is 
pumped  into  the  great  aorta,  and  through  its  branches  distributed  to  the  entire 
body.     The  terminal  arteries  are  continuous  with  the  general  capillaries  of  the 

141 


142  THE    CIRCULATION    OF    THE    BLOOD 

body,  and  these  in  turn  with  the  veins,  which  conduct  the  blood  back  to  the 
right  side  of  the  heart  again.  It  will  be  seen,  therefore,  that  the  circulatory 
apparatus  consists  of  two  great  divisions,  the  pulmonary  and  the  systemic  cir- 
culation. This  arrangement  is  illustrated  by  the  accompanying  figure. 
A  study  of  this  figure  will  show  that  in  certain  regions  of  the  systematic  circu- 
lation there  are  two  capillary  beds  between  the  main  arteries  and  the  main 
veins.  This  subordinate  stream  through  the  liver  is  called  the  portal  cir- 
culation, and  the  similar  arrangement  existing  in  the  kidney  is  called  the 
renal  circulation.  This,  in  general,  is  the  outline  of  the  course  of  the  blood 
in  its  circulation. 

To  make  a  study  of  the  various  phenomena  manifested  in  the  physiology 
of  the  circulatory  apparatus,  it  is  obvious  that  we  have  to  do  with  certain 
fundamental  activities;  first,  the  physiology  of  the  pumping  organ,  the  heart; 
second,  the  behavior  of  the  blood  in  the  arteries,  capillaries,  and  veins;  third, 
the  coordination  of  these  various  divisions  of  the  apparatus  through  the 
nervous  system.  To  understand  this  it  will  be  necessary  to  have  in  mind  in 
detail  the  anatomical  structure  of  the  apparatus  itself. 

ANATOMICAL   CONSIDERATIONS. 

The  Heart.  The  heart  is  contained  in  the  chest  or  thorax,  and 
lies  between  the  right  and  left  lungs,  figure  134,  enclosed  in  a  membranous 
sac,  the  pericardium.  The  pericardium  is  made  up  of  two  distinct  parts, 
an  external  fibrous  membrane,  and  an  internal  serous  layer,  which  not  only 
lines  the  fibrous  sac,  but  also  is  reflected  on  to  the  heart,  which  it  completely 
invests.  These  form  a  closed  sac,  the  cavity  of  which  contains  just  enough 
fluid  to  lubricate  the  two  surfaces,  and  thus  to  enable  them  to  glide  smoothly 
over  each  other  during  the  movements  of  the  heart.  The  vessels  passing  in 
and  out  of  the  heart  receive  investments  from  this  sac  to  a  greater  or  less  degree.. 

The  heart  is  situated  in  the  chest  behind  the  sternum  and  costal  carti- 
lages, being  placed  obliquely  from  right  to  left.  It  is  of  pyramidal  shape, 
with  the  apex  pointing  downward,  outward,  and  toward  the  left,  and  the 
base  backward,  inward,  and  toward  the  right.  The  heart  is  suspended  in 
the  chest  by  the  large  vessels  which  proceed  from  its  base,  but,  excepting 
at  the  base,  the  organ  itself  hangs  free  within  the  sac  of  the  pericardium. 
The  part  which  rests  upon  the  diaphragm  is  flattened,  and  is  known  as  the 
posterior  surface,  while  the  free  upper  part  is  called  the  anterior  surface. 

On  examination  of  the  external  surface,  the  division  of  the  heart  into 
parts  which  correspond  to  the  chambers  inside  of  it  may  be  traced,  for  a 
deep  transverse  groove,  called  the  auriculo-ventricular  groove,  divides  the 
auricles  from  the  ventricles;  and  the  interventricular  groove  runs  between 
the  ventricles,  both  in  front  and  in  the  back,  separating  the  one  from  the 
other.     The  anterior  groove  is  nearer  the  left  margin,  and  the  posterior  nearer 


THE    HEART 


143 


the  right,  as  the  front  surface  of  the  heart  is  made  up  chiefly  of  the  right 
ventricle  and  the  posterior  surface  of  the  left  ventricle.  The  coronary  ves- 
sels which  supply  the  tissue  of  the  heart  with  blood  run  in  the  furrows  or 
grooves;  also  the  nerves  and  lymphatics,  which  are  embedded  in  more  or 
less  fatty  material,  are  found  in  this  groove. 

The  Chambers  of  the  Heart.  The  interior  of  the  heart  is  divided  by  a 
longitudinal  partition  in  such  a  manner  as  to  form  two  chief  chambers  or 
cavities,  the  right  and  the  left.  Each  of  these  chambers  is  again  subdivided 
transversely  into  an  upper  and  a  lower  portion,  called  respectively  the  auricle 


Fig.  134. — Outline  of  Heart,  Lungs,  and  Liver  to  Show  their  Relations  to  each  other  and  to 
the  Chest  Wall.     (Heusman  and  Fisher's  "Anatomical  Outlines.") 


and  the  ventricle,  which  freely  communicate.  The  aperture  of  communica- 
tion, however,  is  guarded  by  valves  so  disposed  as  to  allow  blood  to  pass 
freely  from  the  auricle  into  the  ventricle,  but  not  in  the  opposite  direction. 
There  are  thus  four  cavities  va  the  heart,  the  auricle  and  ventricle  of  one 
side  being  quite  separate  from  those  on  the  other,  figure  135. 

The  right  auricle,  the  right  part  of  the  base  of  the  heart  as  viewed  from 
the  front,  is  a  thin-walled  cavity  of  more  or  less  quadrilateral  shape,  prolonged 
at  one  corner  into  a  tongue-shaped  portion,  the  right  auricular  appendix, 
which  slightly  overlaps  the  exit  of  the  aorta  from  the  left  ventricle. 

The  interior  of  the  auricle  is  smooth,  being  lined  with  the  general  lining 
membrane  of  the  heart,  the  endocardium.  The  superior  and  inferior  vena? 
cavae  open  into  the  auricle.  The  opening  of  the  inferior  cava  is  protected 
and  partly  covered  by  a  membrane  called  the  Eustachian  valve.  In  the 
posterior  wall  of  the  auricle  is  a   slight  depression  called  the  fossa  ovalis, 


144 


THE     CIRCULATION     OF    THE     BLOOD 


which  corresponds  to  an  opening  between  the  right  and  left  auricles,  exist- 
ing in  fetal  life.  In  the  appendix  are  closely  set  elevations  of  the  muscular 
tissue,  covered  with  endocardium,  and  on  the  anterior  wall  of  the  auricle  are 
similar  elevations  arranged  parallel  to  one  another,  called  musculi  pectinati. 


Fig.  135. — The  Right  Auricle  and  Ventricle  Opened  and  a  Part  of  their  Right  and  Anterior  Walls 
Removed  so  as  to  Show  their  Interior.  1,  Superior  vena  cava;  2,  inferior  vena  cava;  2',  hepatic 
veins  cut  short;  3,  right  auricle;  3',  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian  valve; 
3",  is  placed  close  to  the  aperture  of  the  coronary  vein;  t,  t.  placed  in  the  auriculo- ventricular 
groove,  where  a  narrow  portion  of  the  adjacent  walls  of  the  auricle  and  ventricle  has  been  pre- 
served; 4,  4,  cavity  of  the  right  ventricle,  the  upper  figure  is  immediately  below  the  semilunar 
valves;  4',  large  columna  carnea  or  musculus  papillaris;  5,  5',  5",  tricuspid  valve;  6,  placed  in  the 
interior  of  the  pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed 
and  a  narrow  portion  of  it  preserved  at  its  commencement  where  the  semilunar  valves  are  attached; 
7,  concavity  of  the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus;  8,  ascending  part  or  sinus 
of  the  arch  covered  at  its  commencement  by  the  auricular  appendix  and  pulmonary  artery;  9, 
placed  between  the  innominate  and  left  carotid  arteries;  10,  appendix  of  the  left  auricle;  11,  11, 
outside  of  the  left  ventricle   the  lower  figure  near  the  apex.      (Allen  Thomson.) 


The  right  ventricle  forms  the  right  margin  of  the  heart.  It  takes  no 
part  in  the  formation  of  the  apex.  On  section  its  cavity  is  semilunar  or 
crescentic,  figure  137.  Into  it  are  two  openings,  the  auriculo-ventricular 
orifice  at  the  base,  and  the  opening  of  the  pulmonary  artery,  also  at  the  base 
but  more  to  the  left.  The  part  of  the  ventricle  leading  to  the  pulmonary 
artery  is  called  the  conus  arteriosus  or  infiindibulum;  both  orifices  are  guarded 
by  valves,   the  former  called  the  tricuspid  and  the  latter  the  semilunar. 


THE     HEART 


145 


In  this  ventricle  are  also  the  projections  of  the  muscular  tissue  called  the 
columnce  cameo;. 

The  left  auricle  is  situated  at  the  left  and  posterior  part  of  the  base  of 
the  heart.     The  left  auricle  is  only  slightly  thicker  than  the  right  and  its 


Pig.  136.— The  Left  Auricle  and  Ventricle  Opened  and  a  Part  of  Their  Anterior  and  Left  \\  alls 
Removed.  Magnified  h.  The  pulmonary  artery  has  been  divided  at  its  commencement;  the 
opening  into  the  left  ventricle  is  carried  a  short  distance  into  the  aorta  between  two  of  the  segments 
of  the  semilunar  valves;  and  the  left  part  of  the  auricle  with  its  appendix  has  been  removed.  The 
right  auricle  is  out  of  view.  1.  The  two  right  pulmonary  veins  cut  short;  their  openings  are  seen 
within  the  auricle;  1'.  placed  within  the  cavity  of  the  auricle  on  the  left  side  of  the  septum  and  on 
the  part  which  forms  the  remains  of  the  valve  of  the  foramen  ovale,  of  which  the  crescentic  fold  is 
seen  toward  the  left  hand  of  1';  2,  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  preserved 
round  the  auriculo- ventricular  orifice;  3,  3',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to 
become  very  much  thinner  toward  3".  at  the  apex;  4,  a  small  part  of  the  anterior  wall  of  the  left 
ventricle  which  has  been  preserved  with  the  principal  anterior  columna  carnea  or  musculus  papil- 
laris attached  to  it;  5,  5,  musculi  papillares;  5',  the  left  side  of  the  septum,  between  the  two  ven- 
tricles, within  the  cavity  of  the  left  ventricle;  6.  6',  the  mitral  valve;  7.  placed  in  the  interior  of  the 
aorta  near  its  commencement  and  above  the  three  segments  of  its  semilunar  valve  which  are  hang- 
ing loosely  together;  7',  the  exterior  of  the  great  aortic  sinus;  8,  the  root  of  the  pulmonary  artery 
and  its  semilunar  valves;  8',  the  separated  portion  of  the  pulmonary  artery  remaining  attached  to 
the  aorta  by  9,  the  cord  of  the  ductus  arteriosus;  10,  the  arteries  rising  from  the  summit  of  the  aor- 
tic arch.      (Allen  Thomson.) 

form  and  structure  are  the  same  as  in  the  right.     The  left  auricido-ventricii- 
lar  orifice  is  oval  and  a  little  smaller  than  that  on  the  right  side  of  the  heart. 
There  is  a  slight  vestige  on  the  septum  of  the  foramen  between  the  auricles. 
10 


146 


THE    CIRCULATION    OF    THE    BLOOD 


The  left  ventricle  occupies  the  posterior  and  apical  portion  of  the  heart, 
and  is  connected  directly  with  the  great  aorta.  It  is  separated  from  the 
auricle  by  the  bicuspid  or  mitral  valves,  and  the  opening  into  the  great  aorta 
is  guarded  by  the  semilunar  valves.  The  walls  of  the  left  ventricle  are  two 
or  three  times  as  heavy  as  those  of  the  right,  and  may  be  as  much  as  half  an 
inch  in  total  thickness. 

The  left  ventricle  is  capable  of  containing  90  to  120  c.  c.  of  blood.  The 
capacity  of  the  auricles  is  considerably  less  after  death  owing  to  their  con- 
tracted condition.  The  whole  heart  is  about  12  cm.  long  by  8  cm.  at  its 
greatest  width,  and  6  cm.  in  thickness.  The  average  weight  in  the  adult  is 
about  300  grams. 

The  walls  of  the  heart  are  constructed  almost  entirely  of  layers  of  muscu- 
lar fibers;  but  a  ring  of  connective  tissue,  to  which  some  of  the  muscular 
fibers  are  attached,  is  inserted  between  each  auricle  and  ventricle  and  forms 


Fig.  137. — Cross-section  of  a  Completely  Contracted  Human  Heart,  at  the  Level  of  the  Lower 
and  Middle  Thirds.     (According  to  Krehl.) 

the  boundary  of  the  auricnlo-ventricidar  opening.  Fibrous  tissue  also  exists 
at  the  origins  of  the  pulmonary  artery  and  aorta.  The  muscular  fibers  of 
each  auricle  are  in  part  continuous  with  those  of  the  other,  and  in  part  separate; 
and  the  same  holds  true  for  the  ventricles.  The  fibers  of  the  auricles  are, 
however,  quite  separate  from  those  of  the  ventricles,  the  bond  of  connection 
between  them  being  the  fibrous  and  the  embryonic  muscular  tissue  of  the 
auriculo-ventricular  rings  and  the  bundle  of  His  in  the  septum. 

The  development  of  the  heart  shows  that  it  is  derived  from  an  embryonic 
tube,  which  in  its  growth  becomes  twisted  upon  itself  and  divided  into  the 


THE    HEART 


147 


two  main  divisions  that  we  know  in  the  adult.     Anatomical  dissections  have 
shown  that  the  muscles  of  the  ventricles  form  spiral  sheaths  extending  from 


Fig.  138. 


riu  mm. 


Fig. 


Fig.  138. — Cardiac  Muscle  Celts.  Showing  their  Form,  Branches,  Nuclei,  and  Stria?.  From 
the  heart  of  a  young  rabbit.  Magnified  425  diameters.  (Schafer.)  a.  Line  of  junction  between 
the  cells  (intercellular  cement);   b,  c,  branches  of  the  cells. 

Fig.  139. — Cardiac  Muscle  Cells  of  the  Left  Ventricle  of  a  Child  at  Birth  (full  term),  to  show 
the  form  of  the  cells,  their  structural  details,  their  relations  to  one  another,  and  their  general  agree- 
ment with  those  of  cold-blooded  vertebrates.  .4,  Large  cell  with  two  nuclei;  this  cell  has  nearly 
the  proportions  of  those  of  the  adult;  B,  group  of  cells  in  their  natural  relation.  At  the  right  of 
the  middle  cell  are  two  spaces  or  fissures,  n.  Nucleus.  The  transverse  striations  cross  the  nuclei 
in  all  the  cells,  and  each  nucleus  possesses  several  nucleoli.     (Gage.) 


Fig.  140. 


Fig.  141. 


Fig.  140. — Diagram  of  the  Course  of  the  Superficial  Muscle  Layers  Originating  in  the  Right 
and  Left  Auriculo- ventricular  Rings  and  in  the  Posterior  Half  of  the  Tendon  of  the  Conus.  (After 
MacCallum.)     C,  Anterior  papillary  muscle. 

Fig.  141. — Diagram  of  the  Course  of  the  Superficial  Muscle  Layers  Originating  in  the  Anterior 
Half  of  the  Tendon  of  the  Conus.  (After  MacCallum.)  .4,  Posterior  papillary  muscle;  B,  papillary 
muscle  of  the  septum. 


US 


THE    CIRCULATION     OF    TUT-:     BLOOD 


the  base  of  the  two  ventricles  in  spiral  bands  toward  the  apex.  These  bands 
of  muscle  are  wound  about  the  surface  of  the  ventricles  in  the  right-to-left 
direction.  At  the  apex  they  extend  up  into  the  deeper  tissue.  If  the  super- 
ficial muscles  are  dissected  off,  there  is  left  a  great  central  core  of  muscle, 


Fir..   142. 


Fir,.   74^. 


Fig.  142. — Diagram  of  the  Course  of  the  Layer  Superficial  to  the  Deepest  Layer  of  the  Muscle 
of  the  Left  Ventricle,  which  is  shown  in  outline.  The  deepest  layer  is  also  shown.  (After  Mac- 
Callum.)     A ,  Posterior  papillary  muscle;   B,  papillary  muscle  of  the  septum. 

Fig.  143. — Diagram  of  a  Laver  still  more  Superficial  to  that  Shown  in  Pig.  142,  and  Ending 
in  the  Anterior  Papillary  Muscle.  The  deeper  layers  are  represented  in  dotted  lines.  (After 
MacCallum.)  A,  Posterior  papillary  muscle;  B,  papillary  muscle  of  septum;  C,  anterior  papillary 
muscle. 

which  is  described  by  MacCallum  as  running  more  transversely  around  the 
wall  of  one  ventricle,  then  through  the  septum  and  around  the  other  in  a 
reverse  scroll,  figure  142. 

The  Valves  of  the  Heart.  The  valves  of  the  heart  are  arranged 
so  that  the  blood  can  pass  only  in  one  direction.  These  are  the  tricuspid 
valve,  between  the  right  auricle  and  right  ventricle,  figure  135,  and  the  semi- 
lunar valves  of  the  pulmonary  artery,  the  mitral  valve  between  the  left  auricle 
and  ventricle,  and  semilunar  valves  of  the  aorta.  The  bases  of  the  tricuspid, 
figure  152,  and  mitral  valves  are  attached  to  the  walls  of  the  auriculo-ven- 
tricular  rings,  respectively.  Their  ventricular  surfaces  and  borders  are 
fastened  by  slender  tendinous  fibers,  the  chorda  tendinece,  to  the  internal 
surface  of  the  walls  of  the  ventricles  at  points  which  project  into  the  ventricu- 
lar cavity  in  the  form  of  bundles  or  columns,  the  colunnicr  carnea. 

The  semilunar  valves  guard  the  orifices  of  the  pulmonary  artery  and  of 
the  aorta.  They  are  nearly  alike  on  both  sides  of  the  heart,  but  the  aortic 
valves  are  altogether  thicker.  Each  valve  consists  of  three  parts  which  are 
of  semilunar  shape,  the  convex  margin  of  each  being  attached  to  a  fibrous 
ring  at  the  place  of  junction  of  the  artery  to  the  ventricle,  and  the  concave 
or  nearly  straight  border  being  free,  so  as  to  form  a  little  pouch  like  a  pocket, 
7,  figure  136.  In  the  center  of  each  free  edge  cf  the  valves  which  contains 
a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous  nodule,  the  corpus  Arantii. 


THE     ARTERIES 


149 


The  Arteries.  The  arterial  system  begins  at  the  left  ventricle  in 
a  single  large  trunk,  the  aorta,  which,  almost  immediately  after  its  origin, 
gives  off  in  the  thorax  three  large  branches  for  the  supply  of  the  head,  neck, 
and  upper  extremities;  it  then  traverses  the  thorax  and  abdomen,  giving 
off  branches,  some  large  and  some  small,  for  the  supply  of  the  various  organs 
and  tissues  it  passes  on  its  way.  In  the  abdomen  it  divides  into  two  chief 
branches.  The  arterial  branches,  wherever  given  off,  divide  and  subdivide 
until  the  caliber  of  each  subdivision  becomes  very  minute.  These  smallest 
arteries  are  called  arterioles.  These  arterioles  are  continuous  with  the  capil- 
laries. Arteries  frequently  communicate  or  anastomose  with  other  arteries. 
The  arterial  branches  are  usually  given  off  at  an  acute  angle,  and  the  areas 
of  the  branches  of  an  artery  generally  exceed  that  of  the  parent  trunk,  and, 


E?l 


Fig.  144. 


Fig.  145. 


Fig.  m<\ 


Fig.  144. — Minute  Artery  Viewed  in  Longitudinal  Section,  c.  Nucleated  endothelial  mem- 
brane, with  faint  nuclei  in  lumen,  looked  at  from  above;  i,  thin  elastic  tunica  mtima;  m,  muscular 
coat  or  tunica  media;   a,  tunica  adventitia.      (Klein  and  Noble  Smith.) 

Fig.  145. — Transverse  Section  through  a  Large  Branch  of  the  Inferior  Mesenteric  Artery  of  a 
Pig.  e,  Endothelial  membrane;  *;  tunica  elastica  interna,  no  subendothelial  layer  is  seen;  m, 
muscular  tunica  media,  containing  only  a  few  wavy  elastic  fibers;  c,  c,  tunica  elastica  externa,  di- 
viding the  media  from  the  connective-tissue  adventitia,  a.  (Klein  and  Noble  Smith.)  Magnifica- 
tion 350  diameters. 

Fig.  146. — Muscular  Fiber  Cells  from  Human  Arteries.  Magnified  350  diameters.  (Kolliker.) 
a.  Nucleus;    B,  a  fiber  cell  treated  with  acetic  acid. 

as  the  distance  from  the  origin  is  increased,  the  area  of  the  combined  branches 
is  increased  also.  As  regards  the  arterial  system  of  the  lungs,  the  pulmonary 
artery  and  its  subdivisions,  they  are  distributed  in  much  the  same  manner 
as  the  arteries  belonging  to  the  general  systemic  circulation. 

The  walls  of  the  arteries  are  composed  of  three  principal  coats,  the  ex- 
ternal or  tunica  adventitia,  the  middle  or  tunica  media,  and  the  internal  or 
tunica  intima.  The  external  coat,  figures  144  and  145,  a,  the  strongest  and 
toughest  part  of  the  wall  of  the  artery,  is  formed  of  areolar  tissue,  with  which 
is  mingled  throughout  a  network  of  elastic  fibers.     The  middle  coat,  figure 


150 


THE    CIRCULATION    OF    THE     BLOOD 


145,  m,  is  composed  of  both  muscular  and  elastic  fibers  with  a  certain  pro- 
portion of  areolar  tissue.  In  the  larger  arteries,  figure  145,  its  thickness  is 
comparatively  as  well  as  absolutely  much  greater  than  in  the  small  arteries, 
constituting,  as  it  does,  the  greater  part  of  the  arterial  wall.  The  muscular 
fibers  are  unstriped,  figure  146,  and  are  arranged,  for  the  most  part,  trans- 
versely to  the  long  axis  of  the  artery,  figure  144,  m,  while  the  elastic  element, 
taking  also  a  transverse  direction,  is  disposed  in  the  form  of  closely  inter- 
woven and  branching  fibers  intersecting  in  all  parts  the  layers  of  muscular 
fiber.     In  arteries  of  various  size  there  is  a  difference  in  the  proportion  of 


Fig.  147. 


-Vein  and    Capillaries.     Silver-nitrate  and   hematoxylin    stain,  to    show    outlines 
of  endothelial  cells  and  their  nuclei.      (Bailey.) 


the  muscular  and  elastic  element,  elastic  tissue  preponderating  in  the  largest 
arteries  and  unstriped  muscle  in  those  of  medium  and  small  size.  The 
arteries  are  quite  elastic  in  both  large  and  small  vessels.  The  internal  coat 
is  formed  by  a  layer  of  elastic  tissue,  called  the  fenestrated  membrane  of  Henle. 
It  is  peculiar  in  its  tendency  to  curl  up  when  peeled  off  from  the  artery,  and 


Fig.  148. — Network  of  Capillary  Vessels  of  the  Air  Cells  of  the  Horse's  Lung  Magnified,    a,  a. 
Capillaries  proceeding  from  b,  b,  terminal  branches  of  the  pulmonary  artery.     (Frey.) 


in  the  perforated  and  streaked  appearance  which  it  presents  under  the  micro- 
scope. The  inner  surface  of  the  artery  is  lined  with  a  delicate  layer  of  elon- 
gated endothelial  cells,  figure  145,  e,  which  make  it  smooth  and  polished  and 
furnish  a  nearly  impermeable  surface  along  which  the  blood  may  flow  with 
the  smallest  possible  amount  of  resistance  from  friction. 


THE    CAPILLARIES 


151 


Nerves.  Most  of  the  arteries  are  surrounded  by  a  plexus  of  nerves  or 
nerve  fibers,  which  twine  around  the  vessel.  The  smaller  arteries  also  have 
a  delicate  network  of  similar  nerve  fibers  many  of  which  appear  to  end  near 
the  nuclei  of  the  transverse  muscular  fibers. 

The  Capillaries.  In  all  vascular  textures,  except  some  parts  of 
the  corpora  cavernosa  of  the  penis,  of  the  uterine  placenta,  and  of  the  spleen, 


Fig.  149. — Capillaries  of  Striated  Muscular  Tissue.     From  a  cat.     Magnified  300  diameters. 
(Heitzmann.)     .4,  Artery;    V,  vein. 

the  transmission  of  the  blood  from  the  minute  branches  of  the  arteries  to  the 
minute  veins  is  effected  through  a  network  of  capillaries.  They  may  be 
seen  in  all  minutely  injected  preparations. 

The  point  at  which  the  arteries  terminate  and  the  capillaries  commence 
cannot  be  exactly  defined,  for  the  transition  is  gradual.  The  capillaries 
maintain  essentially  the  same  diameter  throughout.  The  meshes  of  the 
network  that  they  compose  are  more  uniform  in  shape  and  size  than  those 
formed  by  the  anastomoses  of  the  minute  arteries  and  veins. 


152  THE     CIRCULATION     OF    THE     BLOOD 

The  walls  of  the  capillaries  are  composed  of  a  single  layer  of  elongated 
or  radiate,  flattened  and  nucleated  endothelial  cells,  so  joined  and  dove- 
tailed together  as  to  form  a  continuous  transparent  membrane,  figure  147. 
Outside  these  cells  in  the  larger  capillaries  there  is  a  structureless  supporting 
membrane  on  the  inner  surface  of  which  they  form  a  lining. 

The  diameter  of  the  capillary  vessels  varies  somewhat  in  the  different 
textures  of  the  body,  the  most  common  size  being  about  12  micromillimeters, 
^oVrr  °f  an  inch.  Among  the  smallest  may  be  mentioned  those  of  the 
brain  and  of  the  follicles  of  the  mucous  membrane  of  the  intestines;  among 
the  largest,  those  of  the  skin,  and  especially  those  of  the  medulla  of  the  bones. 

The  form  of  the  capillary  network  differs  in  the  different  organs  of  the 
body,  but  is  usually  adjusted  to  the  structural  arrangement  of  the  cells  of 
any  given  organ. 

The  capillary  network  is  closest  in  the  lungs  and  in  the  choroid  coat  of 
the  eye.  In  the  human  liver  the  interspaces  are  of  the  same  size,  or  even 
smaller  than  the  capillary  vessels  themselves.  In  the  human  lung  the  spaces 
are  smaller  than  the  vessels;  in  the  human  kidney,  and  in  the  kidney  of  the 
dog,  the  diameter  of  the  injected  capillaries,  compared  with  that  of  the  inter- 
spaces, is  in  the  proportion  of  one  to  four,  or  of  one  to  three.  The  brain 
receives  a  very  large  quantity  of  blood;  but  its  capillaries  are  very  minute 
and  are  less  numerous  than  in  some  other  parts.  In  the  mucous  mem- 
branes, for  example  in  the  conjunctiva  and  in  the  cutis  vera,  the  capillary 
vessels  are  much  larger  than  in  the  brain  and  the  interspaces  narrower, 
namely,  not  more  than  three  or  four  times  wider  than  the  vessels.  In  the 
periosteum  and  in  the  external  coat  of  arteries  the  meshes  are  much  larger, 
their  width  being  about  ten  times  that  of  the  vessels.  It  may  be  held  as  a 
general  rule  that  the  more  active  the  functions  of  an  organ  are,  the  more 
vascular  it  is. 

The  Veins.  The  venous  system  begins  in  small  vessels  which  are 
slightly  larger  than  the  capillaries  from  which  they  spring.  These  vessels 
are  gathered  up  into  larger  and  larger  trunks  until  they  terminate  in  the  two 
venae  cava?  and  the  coronary  vein  which  enter  the  right  auricle,  and  in  four 
pulmonary  veins  which  enter  the  left  auricle.  The  total  capacity  of  the 
veins  diminishes  as  they  approach  the  heart;  but  their  capacity  exceeds  by 
two  or  three  times  that  of  their  corresponding  arteries.  The  pulmonary 
veins,  however,  are  an  exception  to  this  rule.  The  veins  are  found  after 
death  more  or  less  collapsed,  and  often  contain  blood.  They  are  usually 
distributed  in  a  superficial  and  a  deep  set  which  communicate  frequently 
in  their  course. 

The  coats  of  veins  bear  a  general  resemblance  to  those  of  arteries,  figure 
150.  Thus,  they  possess  outer,  middle,  and  inner  coats.  The  outer  coat  is 
constructed  of  areolar  tissue  like  that  of  the  arteries,  but  is  thicker.  In  some 
veins  it  contains  muscular  cells  arranged  longitudinally.     The  middle  coat 


THE    VEINS 


I, 


is  considerably  thinner  than  that  of  the  arteries;  it  contains  circular  un- 
striped  muscular  fibers  mingled  with  a  large  proportion  of  yellow  elastic  and 
white  fibrous  connective  tissue.     In  the  large  veins  near  the  heart  the  middle 


Fig.  150. — Transverse  Section  through  a  Small  Artery  and  Vein  of  the  Mucous  Membrane 
of  a  Child's  Epiglottis;  the  artery  is  thick- walled  and  the  vein  thin- walled.  .4,  Artery;  the  letter 
is  placed  in  the  lume.i  of  the  vessel,  e.  Endothelial  cells  with  nuclei  clearly  visible;  these  cells 
appe  r  very  thick  from  the  contracted  state  of  the  vessel.  Outside  it  a  double  wavy  line  marks 
the  elastic  tunica  intima.  m,  Tunica  media  consisting  of  unstriped  muscular  fibers  circularly  ar- 
ranged; their  nuclei  are  well  seen,  a,  Part  of  the  tunica  adventitia,  showing  bundles  of  connective- 
tissue  fiber  in  section,  with  the  circular  nuclei  of  the  connective-tissue  corpuscles.  This  coat  grad- 
ually merges  into  the  surrounding  connective  tissue.  V,  The  lumen  of  the  vein.  The  other  letters 
indicate  the  same  as  in  the  artery.  The  muscular  coat  of  the  vein,  m,  is  seen  to  be  much  thinner 
than  that  of  the  artery.     X  350.     (Klein  and  Noble  Smith.) 


Fig.  151. — .4,  Vein  with  valves  open.     B,  vein  with  valves  closed;   stream  of  blood   passing 
off  by  lateral  channel.      (Dalton.) 


154  THE    CIRCULATION    OF    THE    BLOOD 

coat  is  replaced  for  some  distance  from  the  heart  by  circularly  arranged 
striped  muscular  fibers  continuous  with  those  of  the  auricles.  The  internal 
coat  of  veins  consists  of  a  fenestrated  membrane  lined  by  endothelium.  The 
fenestrated  membrane  may  be  absent  in  the  smaller  veins.  The  veins  are 
supplied  with  valves  in  certain  regions  of  the  body,  especially  in  the  veins  of 
the  arms  and  legs.  The  general  construction  of  these  valves  is  similar  to 
that  of  the  semilunar  valves  of  the  aorta  and  pulmonary  artery  already 
described.  Their  free  margins  are  turned  in  the  direction  toward  the  heart, 
so  as  to  prevent  any  movement  of  blood  backward.  They  are  commonly 
placed  in  pairs,  at  various  distances  in  different  veins.  In  the  smaller  veins 
single  valves  are  often  met  with,  and  three  or  four  are  sometimes  placed 
together  or  near  one  another  in  the  larger  veins  such  as  in  the  subclavians 
at  their  junction  with  the  jugular  veins.  During  the  period  of  their  in- 
action, when  the  venous  blood  is  flowing  in  its  proper  direction,  they  lie  by 
the  sides  of  the  walls  of  the  veins;  but  when  in  action,  they  come  together 
like  valves  of  the  arteries,  figure  151.  Their  situation  in  the  superficial 
veins  of  the  forearm  is  readily  discovered  by  pressing  along  its  surface,  in  a 
direction  opposite  to  the  venous  current,  i.e.,  from  the  elbow  toward  the  wrist, 
when  little  swellings,  figure  151,  B,  will  appear  in  the  position  of  each  pair 
of  valves. 

Lymphatic  spaces  are  present  in  ihe  coats  of  both  arteries  and  veins; 
but  in  the  tunica  adventitia  or  external  coat  of  the  large  vessels  they  form 
a  distinct  plexus  of  more  or  less  tubular  vessels.  In  smaller  vessels  they 
appear  as  sinus  spaces  lined  by  endothelium.  Sometimes,  as  in  the  arteries 
of  the  omentum,  mesentery,  and  membranes  of  the  brain,  the  pulmonary, 
hepatic,  and  splenic  arteries,  the  spaces  are  continuous  with  vessels  which 
distinctly  ensheath  them,  perivascular  lymphatic  sheaths.  Lymph  channels 
are  said  to  be  present  also  in  the  tunica  media. 

THE    ACTION    OF    THE    HEART. 

The  heart's  action  in  propelling  the  blood  consists  in  the  successive  alter- 
nate contraction,  systole,  and  relaxation,  diastole,  of  the  muscular  walls  of 
the  auricles  and  the  ventricles.  This  activity  furnishes  the  power  which 
keeps  the  blood  moving  through  the  arteries,  capillaries,  and  veins.  The 
heart  in  its  activity  is  like  a  great  force  pump  in  that  it  injects  a  certain  quan- 
tity of  blood  at  each  contraction  into  the  great  arteries.  Owing  to  the  inter- 
action between  this  heart-beat  and  the  peripheral  resistance  to  the  flow  of 
blood,  together  with  the  elasticity  of  the  vessels  themselves,  a  high  pressure 
in  the  arteries  is  maintained  all  the  time.  The  heart's  contractions  then, 
pumping  against  this  high  arterial  tension,  are  sufficient  to  maintain  a  constant 
flow  of  blood  through  the  capillaries,  and,  therefore,  through  the  active  tissues. 

The  heart  beats  at  an  average  rate  of  about  72  times  per  minute  during 


ACTION    OF    THE     HEART  155 

life.  Each  successive  contraction  really  begins  in  the  great  veins,  which 
are  muscular,  and  extends  over  the  auricles  and  ventricles  in  regular  sequence. 
The  contraction  of  each  successive  part  is  called  its  systole  and  the  relaxation 
its  diastole.  The  diastole  covers  the  period  of  active  relaxation  of  the  muscle 
and  the  pause  before  beginning  its  next  contraction.  Each  muscular  cham- 
ber of  the  heart  may,  therefore,  be  said  to  have  its  systole  and  diastole.  The 
whole  series  of  events  from  the  beginning  of  one  contraction  until  the  cor- 
responding event  in  the  next  contraction  is  described  as  the  cardiac  cycle. 

Action  of  the  Auricles.  The  description  of  the  action  of  the  heart 
may  be  commenced  at  that  period  in  each  cycle  in  which  the  whole  heart  is 
at  rest.  The  heart  is  then  in  a  passive  state.  The  auricles  are  gradually 
filling  with  the  blood  flowing  into  them  from  the  veins,  and  a  portion  of  this 
blood  is  passing  at  once  through  the  auricles  into  the  ventricles,  the  opening 
between  the  cavity  of  each  auricle  and  that  of  its  corresponding  ventricle 
being  free  during  the  entire  pause.  The  auricles,  however,  receiving  more 
blood  than  at  once  passes  through  them  to  the  ventricles,  become,  near  the 
end  of  the  pause,  passively  distended.  At  this  moment  a  contraction  wave 
begins  on  the  bases  of  the  venae  cavse  and,  running  down  from  the  walls  of 
the  veins,  passes  to  the  muscular  walls  of  the  auricle.  The  contraction  of  the 
auricles,  the  right  and  left  contracting  at  the  same  time,  forces  the  blood 
into  the  ventricles. 

The  contraction  of  the  muscular  walls  of  the  great  veins  maintains  a 
condition  of  constriction  of  these  veins  during  the  time  of  the  auricular  con- 
traction. This  hinders  the  reflux  of  blood  from  the  auricles  into  the  veins 
during  the  auricular  systole.  Any  slight  regurgitation  from  the  right  auricle 
is  limited  by  the  valves  at  the  junction  of  the  subclavian  and  internal  jugular 
veins  beyond  which  the  blood  cannot  move  backward,  and  by  the  coronary 
vein  which  is  supplied  with  a  valve  at  its  mouth.  The  force  of  the  blood 
propelled  into  the  ventricle  at  each  auricular  systole  is  transmitted  in  all 
directions,  but,  being  insufficient  to  open  the  semilunar  valves,  it  is  expended 
in  distending  the  walls  of  the  ventricle. 

Action  of  the  Ventricles.  The  dilatation  of  the  ventricles  which 
occurs  during  the  latter  part  of  the  diastole  of  the  auricles,  is  completed  by 
the  forcible  injection  of  the  contents  of  the  latter.  The  ventricles,  now  dis- 
tended with  blood,  immediately  begin  to  contract.  The  tricuspid  valves 
are  closed  by  the  initial  reflux  of  blood,  or  possibly  by  the  currents  of  blood 
formed  by  the  sudden  injection  of  the  ventricles  by  the  auricular  contraction. 
The  ventricular  systole  follows  the  auricular  systole  so  closely  that  it  seems 
continuous  with  it.  As  a  result  of  the  ventricular  systole  sufficient  pressure 
is  produced  on  its  contents  to  overcome  the  pressure  against  the  semilunar 
valves  of  the  aorta,  and  the  pulmonary  artery  and  the  ventricles  are  thus 
emptied  completely.  After  the  whole  of  the  blood  has  be~n  expelled  from 
the  ventricles,  the  walls  remain  contracted  for  a  brief  period. 


156  the   circulation   of   the   blood 

The  form  and  position  of  the  fleshy  columns  on  the  internal  walls  of  the 
ventricles  no  doubt  help  to  produce  the  obliteration  of  the  ventricular  cavity 
during  contraction.  The  completeness  of  the  closure  may  often  be  observed 
on  making  a  transverse  section  of  a  heart  shortly  after  death  in  any  case  in 
which  rigor  mortis  is  very  marked,  figure  137.  In  such  a  case  only  a  central 
fissure  may  be  discernible  to  the  eye  in  the  place  of  the  cavity  of  each  ventricle. 
The  arrangement  of  the  muscles  of  the  heart,  as  described  on  page  148,  is 
such  as  to  expend  the  whole  force  of  the  contraction  in  diminishing  the  cavity 
of  the  ventricle,  or,  in  other  words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  diastole  begins.  The 
muscular  walls  relax  and,  by  virtue  of  their  elasticity,  a  slight  negative  press- 
ure is  set  up.  This  negative  or  suctional  pressure  on  the  left  side  of  the 
he:ixt  is  of  importance  in  helping  the  pulmonary  circulation.  It  is  some- 
what inconstant  in  appearance,  but  has  been  found  to  be  equal  to  as  much  as  20 
mm.  of  mercury,  and  is  said  to  be  quite  independent  of  the  aspiratory  power 
of  the  thorax  itself,  which  will  be  described  in  a  later  chapter.  The  ventricles 
now  remain  in  a  state  of  relaxation  or  rest  until  the  next  systole  begins. 

The  duration  of  the  ventricular  systole  and  diastole  has  been  variously 
estimated.  A  computation  of  the  time  of  these  two  phases,  for  man,  in 
figure  153,  reproduced  from  Hurthle,  gives  for  the  systole  0.38  of  a  second, 
and  for  the  diastole  0.4  of  a  second,  with  a  total  of  0.78  of  a  second.  This 
is  equivalent  to  a  rate  of  77  per  minute.  Variations  in  the  time  of  the  systole 
and  the  diastole  of  the  ventricle  falls  chiefly  on  the  pause  of  the  diastole. 

The  ventricles  undergo  little  or  no  change  of  shape  in  the  unopened  chest. 
At  the  moment  in  the  systole  when  the  ventricles  begin  to  discharge  their 
contents  into  the  aorta  and  pulmonary  arteries,  respectively,  there  is  a  sharp 
decrease  in  size  of  the  ventricles.     This  decrease  takes  place  in  all  dimensions. 

Action  of  the  Valves.  The  Auriculo-ventricular  Valves.  Dur- 
ing the  diastole  of  both  auricles  and  ventricles  blood  flows  directly  through 
the  auricles  into  the  ventricles,  the  auricles  during  this  period  acting  as 
continuations  of  the  large  veins  which  empty  into  them.  At  the  end  of 
the  period  the  ventricle  on  each  side  has  already  been  filled  and  distended 
by  the  pressure  of  blood  from  the  veins.  The  systole  of  the  auricle  com- 
pletes this  filling  and  slightly  overdistends  the  ventricle.  When  the  force 
of  the  auricular  contraction  is  spent,  the  ventricular  walls  rebound  slightly 
toward  their  former  position  and  in  so  doing  exert  some  pressure  upon  the 
ventricular  side  of  the  auriculo-ventricular  valves  which  floats  them  upward 
toward  the  auricle.  In  this  connection  another  force  comes  into  play,  viz., 
vortex  or  back  currents  resulting  from  the  flow  of  blood  into  the  ventricle 
under  the  pressure  of  the  auricular  systole.  These  currents  aid  in  floating 
the  valve  leaflets  into  apposition.  Thus,  the  auriculo-ventricular  openings 
are  closed  at  the  end  of  the  auricular  systole,  i.e.,  the  end  of  the  ventricular 
diastole.     The  ventricular  systole  which  follows  simply  serves  to  place  the 


ACTION     OF    THE    VALVES 


157 


valves  under  greater  tension,  thus  closing  them  still  more  firmly.  It  should 
be  recollected  that  the  diminution  in  the  breadth  of  the  base  of  the  heart  in 
its  transverse  diameters  during  the  ventricular  systole  is  especially  marked 
in  the  neighborhood  of  the  auriculo-ventricular  rings,  and  this  aids  in  render- 
ing the  auriculo-ventricular  valves  competent  to  close  the  openings  by  greatly 
diminishing  the  diameter.  The  cusps  of  the  auriculo-ventricular  valves 
meet  not  by  their  edges  only,  but  by  the  opposed  surfaces  of  their  thin  outer 
borders.  The  margins  of  the  valves  are  still  more  secured  in  apposition 
with  one  another  by  the  simultaneous  contraction  of  the  muscular  papillae, 


Fig.  152. — The  Tricuspid  Valves  of  the  Ox,  Closed.    Vertical  section.     (Krehl.) 


whose  chordae  tendineas  have  a  special  mode  of  attachment  for  this  very 
object.  They  compensate  for  the  shortening  of  the  ventricular  walls  and 
thus  prevent  the  valves  from  being  everted  into  the  auricle,  an  event  that 
does  occur  in  certain  valvular  lesions. 

The  actions  of  the  tricuspid  and  mitral  valves  on  the  right  and  left 
sides  of  the  heart  are  essentially  the  same. 

The  Semilunar  Valves.  The  commencement  of  the  ventricular  systole 
precedes  the  opening  of  the  semilunar  valves  by  a  fraction  of  a  second.  The 
intraventricular  pressure  increases  with  the  progress  of  the  systole  until 
there  is  a  distinct  increase  over  the  arterial  pressure,  then  the  opening  of  the 
valves  takes  place  at  once.  They  remain  open  as  long  as  this  difference 
continues.  When  the  diastole  of  the  ventricle  begins  and  the  arterial  blood 
pressure  exceeds  the  intraventricular  pressure,  there  is  an  initial  reflux  of 
blood  toward  the  heart  which  closes  the  semilunar  valves. 


158  THE    CIRCULATION    OF    THE    BLOOD 

The  dilatation  of  the  arteries  is  peculiarly  adapted  to  bring  this  about. 
The  lower  borders  of  the  semilunar  valves  are  attached  to  the  inner  surface 
of  the  tendinous  ring  which  bounds  the  orifice  of  the  artery.  The  tissue  of 
this  ring  is  tough  and  inelastic  and  the  valves  are  equally  inextensible,  being 
formed  mainly  of  tough  fibrous  tissue  with  strong  interwoven  cords.  The 
effect,  therefore,  of  each  propulsion  of  blood  from  the  ventricle  is  to  dilate 
the  wall  of  the  first  portion  of  the  artery  in  the  three  pouches  behind  the 
valves,  while  the  free  margins  of  the  valves  are  drawn  inward  toward  its  center. 
This  position  of  the  valves  and  arterial  walls  is  maintained  while  the  ventricle 
continues  in  contraction;  but  as  soon  as  it  relaxes,  and  the  dilated  arterial 
walls  can  recoil  by  their  elasticity,  the  blood  is  forced  backward  toward  the 
ventricles  and  onward  in  the  course  of  the  circulation.  Part  of  the  blood 
thus  forced  back  lies  in  the  pouches  (sinuses  of  Valsalva)  between  the  valves 
and  the  arterial  walls;  and  the  valves  are  pressed  together  till  their  thin 
lunated  margins  meet  in  three  lines  radiating  from  the  center  to  the  circum- 
ference of  the  artery,  7  and  8,  figure  136.  The  corpora  Arantii  at  the  middle 
of  the  free  margins  insure  a  more  effective  closure. 

The  Sounds  of  the  Heart.  When  the  ear  is  placed  over  the  region 
of  the  heart,  two  sounds  may  be  heard  at  every  beat.  They  follow  in  quick 
succession,  and  are  succeeded  by  a  pause  or  period  of  silence.  The  first 
sound  is  dull  and  prolonged;  its  commencement  coincides  with  the  impulse 
of  the  heart  against  the  chest  wall,  and  just  precedes  the  pulse  at  the  wrist. 


Fig.  153. — Simultaneous  Tracings  of  the  Cardiac  Impact,  or  Cardiogram  (lower),  and  the 
Heart  Tones  (upper),  of  Man.  The  cross  strokes  at  the  beginning  of  the  cardiac  sound  tracing 
and  on  the  cardiogram  mark  the  synchronous  events.      (Hiirthle.) 

The  second  is  shorter  and  sharper,  with  a  somewhat  flapping  character. 
The  periods  of  time  occupied  respectively  by  the  two  sounds  taken  together 
and  by  the  pause  between  the  second  and  the  first  are  unequal.  According 
to  Foster,  the  interval  of  time  between  the  beginning  of  the  first  sound  and 
the  second  sound  is  0.3  of  a  second,  while  between  the  second  and  the  suc- 
ceeding first  it  is  nearly  0.5  of  a  second,  see  figures  153,  154,  and  158.  The 
relative  length  of  time  occupied  by  each  sound,  as  compared  with  the  other, 
may  be  best  appreciated  by  considering  the  different  forces  concerned  in 
the  production  of  the  two  sounds.  In  one  case  there  is  a  strong,  compara- 
tively slow  contraction  of  a  large  mass  of  muscular  fibers,  urging  forward 


THE     SOUNDS    OF    THE     HEART 


159 


a  certain  quantity  of  fluid  against  considerable  resistance;  while  in  the  other 
it  is  a  strong  but  shorter  and  sharper  recoil  of  the  elastic  coat  of  the  large 
arteries — shorter  because  there  is  no  resistance  to  the  flapping  back  of  the 
semilunar  valves  as  there  was  to  their  opening.  The  sounds  may  be  ex- 
pressed by  the  words  lubb — diip.  The  beginning  of  the  first  sound  cor- 
responds in  time  with  the  beginning  of  the  contraction  of  the  ventricles,  the 
closure  of  the  auriculo-ventricular  valves,  and  the  first  part  cf  the  dilatation 
of  the  auricles.  The  sound  continues  through  a  somewhat  longer  interval 
than  the  second  sound.     The  second  sound,  in  point  of  time,  immediately 


o/¥ts     f\ 


Fig.  154. — Simultaneous  Tracings  of  the  Heart  Tone  and  Pulse  of  the  Carotid  in  the  Dog. 
At  and  ,4 2,  First  and  second  sounds;  P,  pulse;  5,  time  in  tenths  and  fiftieths  of  a  second.  (Ein- 
thoven  and  Geluk.) 


follows  the  cessation  of  the  ventricular  contraction,  and  corresponds  with 
the  commencing  dilatation  of  the  ventricles  and  the  opening  of  the  auriculo- 
ventricular  valves,  figure  154. 

The  exact  cause  of  the  first  sound  of  the  heart  is  not  known.  Two  factors 
probably  enter  into  it.  First,  the  vibration  of  the  auriculo-ventricular  valves 
and  of  the  chordae  tendineae.  Second,  the  vibration  of  the  muscular  mass 
of  the  ventricles  themselves.  The  same  mechanical  conditions  produce 
equal  tension  on  the  ventricular  muscle  itself  and,  according  to  the  second 
view,  this  is  sufficient  to  account  for  the  first  sound.  Looking  upon  the 
contraction  of  the  heart  as  a  simple  contraction  and  not  as  a  series  of  con- 
tractions, or  tetanus,  it  is  at  first  sight  difficult  to  see  why  there  should  be 
any  muscular  sound  when  the  heart  contracts. 

The  cause  of  the  second  sound  is  more  simple  and  definite  than  that  of 
the  first.  It  is  entirely  due  to  the  vibration  consequent  on  the  sudden  closure 
of  the  semilunar  valves  when  they  are  pressed  down  across  the  orifices  of 
the  aorta  and  pulmonary  artery.  The  influence  of  these  valves  in  producing 
the  sound  was  first  demonstrated  by  Hope  who  experimented  with  the  hearts 
of  calves.  In  these  experiments  two  delicate  curved  needles  were  inserted, 
one  into  the  aorta,  and  another  into  the  pulmonary  artery  below  the  line  of 


100 


THE     CIRCULATION     OF    THE     KLOOD 


attachment  of  the  semilunar  valves.  After  being  carried  upward  about 
half  an  inch  the  needles  were  brought  out  again  through  the  coats  of  the 
respective  vessels,  so  that  in  each  vessel  one  valve  was  held  back  against 
the  arterial  walls.  Upon  applying  the  stethoscope  to  the  vessels  it  was  found 
that  after  such  an  operation  the  second  sound  had  ceased  to  be  audible. 


Tube  to  communicate 
with  the  tambour 


Ivory     Tape  to  attach 
knob       instrument  to  the  chest 


Tympanum 
Fig.  155. — Cardiograph.      (Sanderson's.) 


Disease  of  these  valves,  when  sufficient  to  interfere  with  their  efficient  action, 
also  demonstrates  the  same  fact  by  modifying  the  second  sound  cr  destroying 
its  distinctness. 

The  Cardiac  Impulse.     The  heart  may  be  telt  to  beat  with  a  slight 
shock  or  impulse  against  the  walls  of  the  chert,  at  the  level  of  the  fifth  inter- 
Screw  to  adjust  the  lever 


Writing  lever 


Tambour 


Tube  to  the  cardiograph 


Fig.  156. — Marey's  Tambour,  to  which  the  Movement  of  the  Column  of  Air  in  the  Cardiograph 
is  Conducted  by  a  Tube,  and  from  which  it  is  Communicated  by  the  Lever  to  a  Revolving  Cylinder 
so  that  the  tracing  of  the  movement  of  the  cardiac  impulse  is  obtained. 

costal  space  on  the  left  side.  Its  extent  and  character  vary  in  different 
individuals,  a  factor  of  considerable  clinical  significance,  and  therefore  es- 
pecially discussed  in  works  on  clinical  diagnosis.  The  cause  of  the  cardiac 
impulse  has  been  variously  described.     It  will  be  remembered  that  during 


THE     CARDIAC     IMPULSE 


161 


the  period  which  precedes  the  ventricular  systole  the  quiet  heart  rests  with  its 
apex  against  the  wall  of  the  chest.  When  the  ventricles  contract,  their  walls 
suddenly  become  firm  and  tense.  Being  firmly  attached  at  the  base  the  effect 
of  the  movement  is  to  press  the  hardened  ventricle  against  the  chest  wall. 
The  discharge  of  the  contents  of  the  ventricle  into  the  curved  aorta  intensi- 
fies this  pressure  by  its  mechanical  effect  in  tending  to  straighten  the  curve 
of  that  vessel  and  thus  holds  the  ventricle  in  firm  contact  with  the  chest. 
It  is  this  sudden  pressure  of  the  contracting  heart  against  the  chest  wall  that 
is  felt  on  the  outside.  The  impact  or  shock  is  possibly  more  distinct  because 
of  the  partial  rotation  of  the  whole  heart  toward  the  right  and  front  along 
its  long  axis.  The  movement  of  the  chest  wall  produced  by  the  ventricular 
contraction  against  it  may  be  registered  by  means  of  an  instrument  called 
the  cardiograph;  and  the  record  or  tracing,  called  a  cardiogram,  corresponds 


Fig.  157. — Typical  Cardiogram  (upper  trace)  from  the  Dog.  Taken  simultaneously  with  the 
aortic  pressure  (middle)  and  intraventricular  pressure  (lower)  tracings.  Time  in  0.0 1  of  a  second. 
(Hiirthle.) 

almost  exactly  with  a  tracing  obtained  by  an  instrument  applied  over  the 
contracting  ventricle  itself. 

The  cardiograph,  figure  156,  consists  of  a  cup-shaped  metal  box  over 
the  open  front  of  which  is  stretched  an  elastic  India-rubber  membrane  upon 
which  is  fixed  a  small  knob  of  hard  wood  or  ivory.  This  knob,  however, 
may  be  attached,  as  in  the  figure,  to  the  side  of  the  box  by  means  of  a  spring, 
and  may  be  made  to  act  upon  a  metal  disc  attached  to  the  elastic  membrane. 

The  knob  is  for  application  to  the  chest  wall  over  the  place  of  the  greatest 
impulse  of  the  heart.  The  box  or  tambour  communicates  by  means  of  an 
air-tight  tube  with  the  interior  of  a  second  or  recording  tambour  supplied 
with  a  long  and  light  writing  lever.  The  shock  of  the  heart's  impulse  being 
communicated  to  the  ivory  knob,  and  through  it  to  the  first  tambour,  the 
effect  is,  of  course,  at  once  transmitted  by  the  column  of  air  in  the  elastic 
11 


162 


THE    CIRCULATION     OF     THE     BLOOD 


tube  to  the  interior  of  the  second  recording  tambour,  also  closed,  and  through 
the  elastic  and  movable  disc  of  the  latter  to  the  writing  lever  which  is  ad- 
justed to  a  registering  apparatus.  This  latter  generally  consists  of  a  cylinder 
or  drum  covered  with  smoked  paper  and  revolving  by  clock-work  with  a 
definite  velocity.  The  point  of  the  lever  writing  upon  the  paper  produces 
a  tracing  of  the  heart's  impulse  or  cardiogram. 

Endocardiac   Pressure.     The   effect   of  the    muscular  contractions 
and  relaxations  of  the  walls  of  the  heart  durinEr  its  svstole  and  diastole  is  to 


Fig.  158. — Double  Cardiac  Sound  for  Simultaneous  Registration  of  the  Blood  Pressure  in  the 
Right  Auricle  and  Ventricle,  or  in  the  Aorta  and  Left  Ventricle.      (Hiirthle.) 

produce  varying  changes  of  pressure  on  its  content  of  blood.  When  this 
pressure  is  measured  by  the  proper  instrument  it  is  found  that  the  pressure 
in  the  left  ventricle  varies  between  wide  ranges.  With  the  beginning  of 
the  muscular  contraction,  the  pressure  rises  till  it  slightly  exceeds  that  of 
the  pressure  of  the  aorta,  remains  high  for  a  brief  interval  of  time,  then  slowly 
and  quietly  decreases  to  less  than  that  of  atmospheric  pressure  and  remains 
low  until  the  beginning  of  the  next  systole.  For  the  right  ventricle  the  events 
and  variations  are  relatively  the  same. 


ENDOCARDIAC     PRESSURE 


163 


In  order  to  determine  the  endocardiac  pressure  communication  must 
be  established  with  the  cavities  of  the  heart.  This  is  accomplished  by  a 
tube  known  as  a  sound,  which  is  introduced  into  the  left  ventricle  by  passing 


Fig.  159. — Simultaneous  Registration  of  Curves  of  the  Left  Intraventricular  Pressure  (lower), 
the  Aortic  Pressure  (middle),  and  the  Cardiac  Impact  (upper).     Time  0.01  of  a  second.     (Hiirthle.) 


Systole 


Diastole/ . 


_  Fig.  160. — Schematic  Cardiogram  I,  and  Intraventricular  Pressure  Curves  from  the  Dog. 
(Hiirthle.)  The  ventricular  pressure  curve  of  the  descending  type  is  represented  by  the  dotted  line. 
Pressure  in  millimeters  of  mercury,  time  in  tenths  of  a  second. 


it  down  the  common  carotid  artery,  or  into  the  right  auricle  and  ventricle 
through  the  jugular  vein.  When  such  tubes  are  introduced  and  connected 
with  some  form  of  pressure-recording  apparatus,  accurate  tracings  of  the 
variations  in  pressure  during  the  heart-beat  are  obtained. 


164 


THE    CIRCULATION    OF    THE     BLOOD 


Chauveau  and  Marey  have  been  able  to  record  and  measure  with  much 
accuracy  the  variations  of  the  endocardiac  pressure  and  the  comparative 
duration  of  the  contractions  of  the  auricles  and  ventricles.  They  placed 
three  small  India-rubber  air-bags  or  sounds  in  the  interior,  respectively,  of 
the  right  auricle,  the  right  ventricle,  and  in  an  intercostal  space  in  front  of 


Fig.  161. — Apparatus  of  MM.  Chauveau  and  Marey  for  Estimating  the  Variations  of  Endo- 
cardiac Pressure,  and  Production  of  the  Impulse  of  the  Heart. 

the  heart  of  living  animals — the  horse.  These  bags  were  connected  by 
means  of  long  narrow  tubes  with  three  levers  arranged  one  over  the  other 
in  connection  with  a  registering  apparatus,  figure  161.  The  synchronism 
of  the  impulse  with  the  contraction  of  the  ventricles  is  also  well  shown  by 


Fig.  162. — Tracings  of  1,  Intra-auricular;   2,  Intraventricular  Pressures;  and  3,  of  the  Cardiac 
Impulse  of  the  Heart.     To  be  read  from  left  to  right.     Obtained  by  Chauveau  and  Marey. 


means  of  the  same  apparatus,  and  the  causes  of  the  several  vibrations  of 
which  it  is  really  composed  have  been  demonstrated. 

In  the  tracing,  figure  162,  the  intervals  between  the  vertical  lines  rep- 
resent periods  of  a  tenth  of  a  second.  The  parts  on  which  any  given  vertical 
line  falls  represent  simultaneous  events.     It  will  be  nees  that  the  contraction 


ENDOCARDIAL     PRESSURE 


165 


of  the  auricle,  indicated  by  the  marked  curve  at  A  in  the  first  tracing,  causes 
a  slight  increase  of  pressure  in  the  ventricle  which  is  shown  at  A'  in  the  second 
tracing,  and  produces  also  a  slight  impulse,  which  is  indicated  by  A"  in  the 
third  tracing.  The  closure  of  the  semilunar  valves  causes  a  momentarily 
increased  pressure  in  the  ventricle  at  Dr,  affects  the  pressure  in  the  auricle  D, 
and  is  also  shown  in  the  tracing  of  the  cardiac  impulse  D". 

The  large  curve  of  the  ventricular  and  the  impulse  tracings,  between 
A'  and  D',  and  A"  and  D",  are  caused  by  the  ventricular  contraction,  while 
the  smaller  undulations,  between  B  and  C,  B'  and  C,  B"  and  C",  are  caused 


Fig.  163. — Apparatus  for  Recording  the  Endocardiac  Pressure.      (Rolleston.) 

by  the  vibrations  consequent  on  the  tightening  and  closure  of  the  auriculo- 
ventricular  valves. 

It  seems  by  no  means  certain  that  Marey's  curves  properly  represent 
the  variations  in  intraventricular  pressure.  Objection  has  been  taken  to 
his  method  of  investigation:  First,  because  his  tambour  arrangement  does 
not  admit  of  both  positive  and  negative  pressure  being  simultaneously  re- 
corded; second,  because  the  method  is  applicable  only  to  large  animals, 
such  as  the  horse;  third,  because  the  intraventricular  changes  of  pressure 
are  communicated  to  the  recording  tambour  by  a  long  elastic  column  of  air; 
and  fourth,  because  the  tambour  arrangement  has  a  tendency  to  record 
inertia  vibrations.  H.  D.  Rolleston,  who  has  pointed  out  the  above  im- 
perfections of  Marey's  method,  has  reinvestigated  the  subject  with  a  more 
suitable  apparatus. 


Kit; 


THE     CIRCULATION     OF     THE     BLOOD 


The  method  adopted  by  Rolleston  is  as  follows: 

A  window  is  made  in  the  chest  of  an  anesthetized  and  curarized  animal,  and  an  appro- 
priately curved  glass  cannula  introduced  through  an  opening  in  the  auricular  appendix. 
The  cannula  is  then  passed  through  the  auriculo-ventricular  orifice  without  causing  any 
appreciable  regurgitation,  into  the  auricle,  or  it  may  be  introduced  into  the  cavity  of  the 
right  or  left  ventricle  by  an  opening  made  in  the  apex  of  the  heart.  In  some  experiments 
the  trocar  is  pushed  through  the  chest  wall  into  the  ventricular  cavity.     His  apparatus 


Fig.  164. — Endocardiac  Pressure  Curve  from  the  Left  Ventricle  of  the  Dog.  The  thorax  was 
opened  and  a  cannula  introduced  through  the  apex  of  the  ventricle;  the  abscissa  is  the  line  of  at- 
mospheric pressure.  5  to  D  represents  the  ventricular  contraction;  from  D  to  the  next  rise  at  G 
represents  the  ventricular  diastole.  The  notch,  at  the  top  of  which  is  F,  is  a  post- ventricular  rise 
in  pressure  from  below  that  of  the  atmosphere,  and  not  a  presystolic  or  auricular  rise  in  pressure. 

is  filled  with  a  solution  of  leech  extract  in  0.75  per  cent  saline  solution,  or  with  a  solution 
of  sodium  bicarbonate  of  specific  gravity  1083. 

The  animals  employed  were  chiefly  dogs.  The  movement  of  the  column  of  blood  is 
communicated  to  the  writing  lever  by  means  of  a  vulcanite  piston  which  moves  with  little 
friction  in  a  brass  tube  connected  with  a  glass  cannula  by  means  of  a  short  connecting 
tube. 

When  the  lower  part  of  the  tube,  A,  is  placed  in  communication  with  one  of  the  cavities 
of  the  heart,  the  movements  of  the  piston  are  recorded  by  means  of  the  lever,  C.  Attached 
to  the  lever  is  a  section  of  a  pulley,  H,  the  axis  of  which  coincides  with  that  of  the  steel  rib- 


Fig.  165. — Curve  with  a  Dicrotic  Summit  from  the  Left  Ventricle;   the  Abscissa  Shows  the  At- 
mospheric Pressure. 

bon,  E ;  while,  firmly  fixed  to  the  piston,  is  the  curved  steel  piston  rod,  /,  from  the  top  of 
which  a  strong  silk  thread,  J,  passes  downward  into  the  groove  on  the  pulley. 

This  thread,  J,  after  being  twisted  several  times  round  a  small  pin  at  the  side  of  the  lever, 
enters  the  groove  in  the  pulley  from  above  downward,  and  then  passes  to  be  fixed  to  the 
lower  part  of  the  curve  on  the  piston  rod  as  shown  in  the  smaller  figure. 

The  movement  of  the  lever,  C,  is  controlled  by  the  resistance  to  torsion  of  the  steel 
ribbon,  E,  to  the  middle  of  which  one  end  of  the  lever  is  securely  fixed  by  a  light  screw 
clamp,  F.     At  some  distance  from  this  clamp,  the  distance  varying  with  the  degree  of  re- 


ENDOCARDIAL'     PRESSURE 


167 


sistancc  which  it  is  desired  to  give  to  the  movements  of  the  lever,  are  two  holders,  G,  G', 
which  securely  clamp  the  steel  ribbon. 

As  the  torsion  of  a  steel  wire  or  strip  follows  Hooke's  law,  the  torsion  being  proportional 
to  the  twisting  force,  the  movements  of  the  lever  point  are  proportional  to  the  force  em- 
ployed to  twist  the  steel  strip  of  ribbon — in  other  words  to  the  pressures  which  act  on  the 
piston,  B.  To  make  it  possible  to  record  satisfactorily  the  very  varying  ventricular  and 
auricular  pressures,  the  resistance  to  torsion  of  a  steel  ribbon  adapts  itself  very  conven- 
iently. 

This  resistance  can  be  varied  in  two  ways,  ist,  by  using  one  or  more  pieces  of  steel 
ribbon  or  by  using  strips  of  different  thicknesses;  or,  2d,  by  varying  the  distance  between 
the  holders,  G,  G",  and  the  central  part  of  the  steel  ribbon  to  which  the  lever  is  attached. 

Rolleston's  conclusions  are:  That  there  is  no  distinct  and  separate 
auricular  contraction  marked  in  the  pressure  curves  obtained  from  the  right 
or  the  left  ventricle,  the  auricular  and  ventricular  rises  of  pressure  being 
merged  into  one  continuous  rise.     He  concludes  that  the  auriculo-ventricular 


Fig.  166. — Hiirthle's  Spring  Manometer.     .4,  Viewed  from  the  side;  B,  viewed  from  the  top. 


valves  are  closed  before  any  great  rise  of  pressure  within  the  ventricle  above 
that  which  results  from  the  auricular  systole,  a,  figure  165.  The  closure  of 
the  valve  occurs  probably  in  the  lower  third  of  the  rise  AB,  figure  165,  and 
does  not  produce  any  notch  or  wave.  It  is  shown  that  the  semilunar  valves 
open  at  the  point  in  the  ventricular  systole,  situated  at  C,  about  or  a  little 
above  the  junction  of  the  middle  and  upper  thirds  of  the  ascending  line  .  1  B, 
and  the  closure  about  or  a  little  before  the  shoulder,  D.  The  figures  show, 
.  finally,  that  the  minimum  pressure  in  the  ventricle  may  fall  below  that  of  the 
atmosphere,  but  that  the  amount  varies  considerably. 

On  the  whole,  the  most  satisfactory  recording  instrument  for  the  measure- 
ment of  endocardiac  pressures  is  the  membrane  manometer  devised  by 
Hiirthle.  This  instrument  avoids  mechanical  errors  in  a  most  satisfactory 
manner.  By  simultaneous  tracings  of  the  pressure  in  the  ventricle  and  in 
the  aorta  by  Hiirthle's  differential  manometer,   the  exact  moment  of  the 


168 


THE    CIRCULATION    OF    THE     BLOOD 


opening  and  closing  of  the  semilunar  valves  has  been  determined.  By 
similar  methods  we  have  been  able  to  fix  synchronism  between  other  events 
occurring  during  the  beat.  These  we  will  summarize  in  the  following  section. 
Cardiac  Cycle.  The  entire  series  of  occurrences  in  a  single  heart- 
beat is  called  the  Cardiac  Cycle.  If  the  condition  of  the  heart  is  considered 
at  that  moment  when  its  muscular  walls  are  at  rest  it  will  be  found  that  the 
auriculo-ventricular  valves  are  open,  that  the  blood  is  flowing  from  the  great 


impulse 


Fig.  167. — Diagrammatic  Representation  of  the  Events  of  the  Cardiac  Cycle.  For  events 
which  occur  in  sequence,  read  in  the  direction  of  the  curved  arrow;  for  synchronous  events,  read 
from  the  center  to  the  periphery  in  any  direction.      (Coleman.) 


veins  into  the  auricle  and  ventricle,  which  form  a  continuous  cavity,  and 
that  the  pressure  is  about  that  of  the  atmosphere,  but  slowly  rising.  Now  a 
wave  of  contraction  begins  on  the  great  veins  and  extends  toward  the  auri- 
cles, which  immediately  contract  and  discharge  their  blood  into  the  ventri- 
cles, somewhat  distending  their  walls.  At  this  moment  the  ventricular 
systole  begins,  the  tricuspid  (and  mitral)  valves  are  closed,  the  flow  of  blood 
into  the  ventricles  is  checked,  and  the  first  heart  sound  is  heard.  The  con- 
traction of  the  ventricles  produces  a  rapidly  rising  pressure  on  the  enclosed 


CARDIAC     CYCLE  169 

contents  until  the  pressure  exceeds  that  in  the  pulmonary  artery  (and  aorta), 
the  semilunar  valves  open,  and  the  blood  is  discharged  into  the  arteries. 
The  ventricles  ordinarily  remain  contracted  for  a  brief  moment  after  their 
contents  are  emptied. 

The  ventricular  diastole  begins  next  and  with  the  initial  relaxation,  and 
the  first  slight  fall  of  the  intraventricular  pressure  below  that  of  the  aorta, 
the  semilunar  valves  close  and  the  second  sound  is  heard.  The  relaxation 
rapidly  proceeds  and  the  intraventricular  pressure  drops  to  below  atmos- 
pheric pressure,  the  auriculo-ventricular  valves  fall  open,  the  blood  that  has 
been  accumulating  in  the  auricles  flows  into  the  ventricles,  and  the  whole 
heart  is  in  the  state  of  pause  described  as  the  point  of  beginning. 

The  duration  of  the  cardiac  cycle  varies  with  the  heart  rate.  With  a 
rate  of  75  per  minute,  the  cardiac  cycle  will  take  0.8  of  a  second.  In  round 
numbers  the  systole  of  the  auricle  takes  0.1  of  a  second  with  a  diastole  of 
0.7  of  a  second,  0.6  of  which  is  in  the  pause  or  rest  period.  The  ventricle 
requires  about  0.3  of  a  second  for  the  systole,  0.5  of  a  second  for  the  dias- 
tole, with  0.2  to  0.3  of  this  for  the  pause.  It  is  evident  that  the  whole  heart 
is  at  rest  at  the  same  instant  for  from  0.1  to  0.2  of  a  second. 

The  relations  of  the  cardiac  sounds  to  the  systole  and  the  diastole  have 
been  graphically  recorded  by  Hiirthle,  figure  153,  page  158,  and  by  Einthoven 
and  Geluk,  figure  154,  page  159.  The  former  found  that  in  a  heart-beat  last- 
ing 0.76  of  a  second  the  interval  of  time  between  the  beginning  of  the  first 
and  second  sounds  was  0.25  of  a  second,  and  that  the  sounds  occur  just  at  the 
beginning  of  the  ventricular  systole  and  diastole  respectively. 

During  the  cardiac  cycle  the  ventricles  are  completely  closed  from  the 
moment  of  the  beginning  of  the  ventricular  systole  until  the  pressure  amounts 
to  a  little  greater  than  the  pressure  in  the  corresponding  arteries,  which 
takes  about  0.2  of  a  second.  From  the  opening  of  the  semilunar  valves 
until  the  closure  of  those  valves,  about  0.15  of  a  second,  the  ventricular  cavity 
is  in  open  communication  with  the  arteries.  There  is,  during  the  diastole, 
a  second  moment  of  complete  closure  of  the  ventricles,  from  the  time  of  the 
closing  of  the  semilunar  valves  until  the  ventricular  pressure  falls  below  the 
auricular  pressure  which  permits  the  auriculo-ventricular  valves  to  open. 

The  Force  of  the  Cardiac  Action.  In  estimating  the  amount  of 
work  done  by  a  machine  it  is  usual  to  express  it  in  terms  of  work  units.  A 
convenient  work  unit  for  this  purpose  is  the  amount  of  energy  required  to 
lift  a  unit  of  weight,  i.e.,  1  gram  or  1  kilogram,  through  a  unit  of  height,  i.e., 
1  centimeter  or  1  meter,  the  work  required  being  1  gramcentimeter  for  small 
units,  and  1  kilogrammeter  for  large  units,  respectively.  The  average  work 
done  by  the  heart  at  each  contraction  can  be  readily  computed  by  multi- 
plying the  weight  of  blood  expelled  by  the  ventricle  by  the  height  through 
which  it  would  have  to  be  lifted  to  overcome  the  resistance  to  its  discharge 
from  the  cavities  into  the  arteries. 


170  THE    CIRCULATION     OF    THE     BLOOD 

The  quantity  of  blood  expelled  and  the  pressure  of  the  arteries  can  only 
be  estimated  for  man.  But  the  computations  from  indirect  observations 
on  other  mammals  indicate  that  the  quantity  of  blood  discharged  from  each 
ventricle  at  a  single  contraction  is  from  80  to  100  c.c.  The  pressure  of  the 
aorta,  see  page  192,  is  an  average  of  say  150  mm.  of  mercury,  or  200  cm.  of 
blood.  The  pressure  in  the  pulmonary  artery  is  much  less,  say  30  mm.  (20 
to  40),  of  mercury  or  40  cm.  of  blood.  Collecting  these  facts  we  have  the 
following  computation: 

Against 

Pressure  Work  in 

Blood  Column  of  Gramcenti- 

Discharged.  Blood.  meters. 

The  left  ventricle    90  c.c.  200  cm.  18,000 

The  right  ventricle go  c.c.  40  cm.  3,600 

Total 90  c.c.  240  cm.  21,600 

This  computation  shows  that  each  heart-beat  expends  21,600  gramcenti- 
meters  (21.6  grammeters)  of  work.  The  amount  of  energy  developed  in  the 
contractions  of  the  auricles  may  be  ignored  in  this  calculation,  which  is  at 
best  only  of  relative  value.  Calculations  based  on  the  determinations  of 
Vierordt,  also  other  earlier  determinations,  give  much  higher  figures  than 
are  presented  here. 

The  Properties  of  the  Heart  Muscle.  It  is  evident  that  if  we  are 
to  arrive  at  any  adequate  explanation  of  the  action  of  the  heart,  one  of  the 
first  questions  that  must  be  considered  is,  what  are  the  fundamental  properties 
of  heart  muscle,  as  such? 

It  has  already  been  shown,  page  61,  that  the  muscular  fibers  of  the 
heart  differ  in  structure  from  skeletal  muscle  fibers  on  the  one  hand,  and 
from  unstriped  muscle  on  the  other,  occupying  an  intermediate  position 
between  the  two  varieties.  The  heart  muscle,  however,  possesses  a  property 
which  is  not  possessed  by  skeletal  muscle,  or  by  unstriped  muscle  to  such  a 
degree,  namely,  the  property  of  contracting  rhythmically. 

Rhythmkity.  The  property  of  rhythmic  contraction  is  shown  by  the 
action  of  the  heart  within  the  body;  its  systole  is  followed  by  its  diastole  in 
regular  sequence  throughout  the  life  of  the  individual.  The  force  and  fre- 
quency of  the  systole  may  vary  from  time  to  time  as  occasion  requires,  but 
there  is  no  interruption  to  the  action  of  the  normal  heart  or  any  interference 
with  its  rhythmical  contractions.  Further,  in  an  animal  rapidly  bled  to 
death,  the  heart  continues  to  beat  for  a  time,  varying  in  duration  with  the 
kind  of  animal  experimentally  dealt  with  and  depending  on  whether  or  not 
there  is  entire  absence  of  blood  within  the  heart  chambers.  Furthermore, 
if  the  heart  of  an  animal  be  removed  from  the  body,  it  still  continues,  for  a 
varying  time,  its  alternate  systolic  and  diastolic  movements.  Thus  we  see 
that  the  power  of  rhythmic  contraction  depends  neither  upon  connection 
with  the  central  nervous  system  nor  yet  upon  the  stimulation  produced  by 


THE    PROPERTIES     OF    THE     HEART    MUSCLE 


171 


the  presence  of  blood  within  its  chambers.  Whether  or  not  rhythmicity  is 
a  property  of  heart  muscle,  as  such,  was  conclusively  settled  by  Gaskell  and 
by  numerous  later  investigators  by  a  very  simple  process.     Gaskell  cut  thin 


Fig.  169. 


Fig.  168. — The  Heart  of  a  Frog  (Rana  esculenta),  from  the  Front.  V,  Ventricle;  Ad,  right 
auricle;   .4s.  left  auricle;    B,  bulbus  arteriosus,  dividing  into  right  and  left  aorta?.      (Ecker.) 

Fig.  169. — The  Heart  of  a  Frog  (Rana  esculenta),  from  the  Back.  5.  v.,  Sinus  venosus  opened; 
c.  s.  s.,  left  vena  cava  superior;  c.  t.  d.,  right  vena  cava  superior;  c.  i.,  vena  cava  inferior;  v.  p., 
vena  pulmonales;  .4.  d.,  right  auricle;  A.  s.  left  auricle;  .4.  p.,  opening  of  communication  between 
the  right  auricle  and  the  sinus  venosus.      X  2^-3.      (Ecker.) 

strips  of  the  apex  of  the  ventricle  of  the  terrapin,  which  is  free  from  the  nerve 
cells,  at  least  nerve  ganglia,  and  found  that  they  contracted  rhythmically 
for  hours.     This  experiment  has  become  a  classic  one  for  the  study  of  the  car- 


FlG.  170. — Automatic  Contractions  of  Sinus  Muscle  from  the  Terrapin's  Heart  in  0.7  per  cent 
Sodium  Chloride.     Time  in  minutes.      (New  figure  by  L.  Frazier.) 


diac  muscular  tissue.  Strips  of  cardiac  muscle  cut  from  the  auricle  and 
from  the  contractile  walls  of  the  venae  cavae,  or  sinus  venosus,  of  the  terra- 
pin also  contract  rhythmically.  If  the  strips  of  muscle  are  kept  moist  with  the 
same  blood  or  serum,  then  the  rhythm  of  the  sinus  is  greater  than  that  of  the 


175 


THE     CIKCUIiATION     OF    TFFK     HUH)  I") 


auricle,  and  that  of  the  auricle  greater  than  that  of  the  ventricle,  a  difference 
that  is  based  on  a  physiological  differentiation  of  the  tissue.     The  sinus 
muscle  is  also  more  delicately  responsive  to  stim- 
uli than  is  the  ventricular  muscle,  i.e.,  it  is  more 
irritable. 

Porter  has  performed  the  more  difficult  ex- 
periment of  isolating  a  small  disc  of  muscle  from 
the  ventricle  of  the  dog,  leaving  only  the  delicate 
nutrient  artery  through  which  the  muscle  was 
fed  with  defibrinated  blood.  This  isolated  small 
piece  of  ventricle  contracted  vigorously  for  many 
minutes.  We  may  conclude,  then,  that  the 
mammalian  heart  muscle  is  also  automatically 
rhythmic. 

Tonicity.  Cardiac  muscle  is  characterized  by 
its  maintaining  a  constant  degree  of  partial  con- 
traction described  as  muscle  tone,  or  tonicity. 
This  property  is  possessed  by  all  parts  of  the 
heart.  In  the  auricle,  however,  and  especially  in 
the  muscular  walls  of  the  sinus  and  veins,  there  is 
considerable  variation  in  tonicity.  Botazzi  showed 
that  in  the  auricle  of  the  toad  the  variations  of 
tone  were  wave-like  and  periodic,  even  though  the 
auricle  were  contracting  with  its  ordinary  funda- 
mental rhythm.  Howell  has  published  numerous 
experiments  showing  tone  waves  in  auricular  and 
sinus  muscle  of  the  terrapin,  in  which  muscle  there 
may  or  may  not  be  occurring  at  the  same  time 
the  ordinary  fundamental  rhythmic  contractions, 
figure  170. 

Irritability  0}  Heart  Muscle.  Mention  was 
made  above  of  the  difference  in  irritability  of  heart 
muscle  chosen  from  different  parts  of  the  heart. 
The  irritability  of  the  muscle  of  each  part  also 
varies  during  the  different  stages  of  the  contrac- 
tion. When  a  contraction  occurs,  experiment 
shows  that  the  muscle  is  not  irritable  to  a  special 
stimulus  applied  at  any  time  from  the  beginning 
of  the  contraction  until  the  summit  of  the  con- 
traction is  reached.  This  is  called  the  refractory 
period.  From  the  summit,  through  the  relaxation 
and  succeeding  pause,  the  irritability  rapidly  in- 
creases until  the  beginning  of  the  next  contraction. 


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THE    PROPERTIES     OF    THE     HEART     MUSCLE 


173 


Considering  the  automatically  contracting  muscle,  the  point  in  which  the 
automatic  contraction  is  released,  i.e.,  begins,  is  the  point  of  maximal  irri- 
tability. It  is  the  moment  when  the  irritability  is  so  great  that  the  muscular 
equilibrium  is  no  longer  stable,  and  the  physiological  contraction  results. 


0.03  y0/rcl 


Fig.  172. — Automatic  Contractions  of  a  Strip  of  Ventricular  Muscle  from  the  Apex  of  the 
Terrapin's  Heart  contracting  in  0.7  percent  Sodium  Chloride;  from  +  to  +  0.03  per  cent  Potassium 
Chloride  is  added  to  the  Sodium  Chloride.  The  rhythm  is  recovered  very  slowly  when  the  muscle 
isreturnedto  0.7-per-cent  sodium  chloride.  Time  in  minutes  (upper)  and  seconds  (lower  stroke). 
(New  figure  by  VVatkins  and  Elliott.) 

The  irritability  of  heart  muscle  is  very  sharply  influenced  by  its  condition 
of  nutrition,  especially  by  the  inorganic  salts  present  in  the  blood  and  lymph, 
see  page  178.  The  salt  content  of  the  blood  comprises  about  0.7  per  cent  sodium 


Fig.  173. — Automatic  Contractions  of  a  Strip  of  Ventricular  Muscle  from  the  Apex  of  the 
Terrapin's  Heart,  a,  Contracting  in  0.7  per  cent  sodium  chloride;  b,  when  0.03  per. cent  calcium- 
chloride  solution  is  added.     Time  in  minutes.      (New  figure  by  L.  Frazier.) 


chloride,  0.03  per  cent  potassium  chloride,  and  0.025  to  0.03  per  cent  cal- 
cium (phosphate  probably),  as  well  as  traces  of  other  metal  bases.  The 
heart  muscle  has  been  shown  by  numerous  investigators  to  be  delicately 


174  THE    CIRCULATION     OF    THE     HLOOB 

responsive  to  the  proportions  of  these  salts  in  the  blood,  or  in  any  artificial 
solution  which  may  be  substituted  for  blood.  If  the  rhythm  is  to  be  taken 
as  an  index  of  the  irritability,  then  an  increase  of  sodium  and  calcium  salts 
increases  the  irritability  (rhythm),  while  the  influence  of  an  increase  in  potas- 
sium is  to  depress  the  irritability  (rhythm). 

Cardiac  Contractions  Always  Maximal.  The  heart  muscle  exhibits 
another  property  which  distinguishes  it  from  ordinary  skeletal  muscle,  viz.,  the 
way  in  which  it  reacts  to  stimuli.  The  latter,  Chapter  XIII,  reacts  slightly 
to  a  stimulus  little  above  the  minimal,  and  with  an  increase  of  the  strength 
of  the  stimulus  will  give  contractions  of  increasing  amplitude  until  the  maxi- 
mum contraction  is  reached.     In  the  case  of  the  heart-beats  this  is  not  so, 


Fig.  174. — Refractory  Period  in  the  Ventricular  Strip  of  the  Terrapin. 

since  the  minimal  stimulus  which  has  any  effect  is  followed  by  the  maximum 
contraction ;  in  other  words,  the  weakest  effectual  stimulus  brings  out  as 
great  a  contraction  as  the  strongest.  If  a  contraction  is  induced  earlier  than 
it  would  automatically  occur,  then  the  succeeding  pause  is  longer,  i.e.,  there 
is  a  compensatory  pause.  Also  the  contraction  induced  is  smaller  and  the 
one  following  the  compensatory  pause  is  proportionately  larger.  This  ob- 
servation can  easily  be  demonstrated  on  the  heart  strip,  see  figure  174,  or  on 
the  whole  ventricle  of  the  frog,  which  was  originally  used  by  Bowditch. 

Nerve  influence,  nutrition,  temperature,  etc.,  will  of  course  affect 
the  extent  of  the  contractions,  but  under  a  given  set  of  conditions  it  is  held 
that  the  contractions  which  occur  are  maximal  for  the  particular  state.  This 
is  more  readily  understood  when  taken  in  connection  with  the  fact  that  when 
a  contraction  originates  in  a  cardiac  cell  it  is  conducted  throughout  the  ex- 
tent of  all  the  cells  of  the  muscular  mass. 

Theories  of  the  Heart-Beat.  The  cause  of  the  rhythmic  power 
of  the  heart  as  a  whole  has  been  the  subject  of  much  discussion  and  experi- 
mental   observation.     Two   leading   hypotheses    have   given   inspiration   to 


THEORIES    OF    THE     HEART-BEAT 


175 


investigators,  and  now  one,  now  the  other  theory  has  attracted  followers 
as  new  facts  have  been  discovered.  The  hypotheses  that  have  been  ad- 
vanced to  explain  the  heart-beat  are  known  as  the  neurogenic  theory  and  the 
myogenic  theory,  respectively. 

The  heart  has  long  been  known  to  have  the  power  of  rhythmic  contrac- 
tions after  removal  from  the  body  and  after  all  connection  with  the  central 
nervous  system  has  been  destroyed.  The  isolated  heart,  even  of  man,  will 
contract  with  good  rhythm  when  kept  at  the  proper  temperature  and  given 
the  proper  nutritive  fluid. 

The  Neurogenic  Theory.  The  neurogenic  theory  attributes  the  remark- 
able power  of  the  heart  to  continue  its  contractions  after  removal  from  the 
body,  and  presumably  while  in  the  body,  to  the  presence  of  the  local  collec- 
tions of  nerve  cells.     The  local  nervous  mechanism  in  the  frog  consists  of 


Fig.  X75. — Course  of  the  Nerves  in  the  Auricular  Partition,  Heart  of  a  Frog,     d,  Wall  of  the 
dorsal  branch;   v,  ventral  branch.     (Ecker.) 

three  chief  groups  of  cells  or  ganglia.  The  first  group  is  situated  in  the 
wall  of  the  sinus  venosus  at  the  junction  of  the  sinus  with  the  right  auricle, 
Remak's  ganglia;  the  second  group  is  placed  near  the  junction  between 
the  auricles  and  ventricles,  Bidder's  ganglia;  and  the  third  in  the  septum 
between  the  auricles,  von  Bezold's  ganglia.  Small  ganglia  have  been  de- 
scribed for  the  base  of  the  ventricle,  but  no  ganglia  are  present  in  the  apical 
part  of  the  ventricles,  though  isolated  cells  have  been  found.  The  nerve- 
cells  of  which  these  ganglia  are  composed  are  generally  unipolar,  seldom 
bipolar.  Sometimes  two  cells  are  said  to  exist  in  the  same  envelope,  con- 
stituting the  twin  cells  of  Dogiel.  The  cells  are  large,  and  have  very  large 
round  nuclei  and  nucleoli,  figure  176.  As  regards  the  automatic  move- 
ments of  the  heart  when  removed  from  the  body,  our  knowledge  has  been 
derived  from  the  study  of  the  hearts  of  the  frog,  tortoise,  dog,  cat,  and  rabbit. 


170 


THE    CIRCULATION     OP    THE     BLOOD 


If  removed  from  the  body  entire,  the  frog's  or  terrapin's  heart  will  con- 
tinue to  contract  for  many  hours  and  even  days,  and  the  contraction  has  no 
apparent  difference  from  the  contraction  of  the  heart  before  removal;  it 
will  take  place,  as  we  have  mentioned,  without  the  presence  of  blood  or 
other  fluid  within  its  chambers.  Not  only  is  this  the  case,  but  the  auricles 
and  ventricle  may  be  cut  off  from  the  sinus,  and  both  parts  continue  to  pul- 
sate; and,  further,  the  auricles  may  be  divided  from  the  ventricle,  with  the 
same  result.  If  the  heart  be  divided  lengthwise,  its  parts  will  continue  to 
pulsate  rhythmically.  The  ventricle  remains  comparatively  quiet,  contrac- 
tions occurring  at  longer  intervals,  if  at  all.  However,  the  ventricle  remains 
irritable  so  long  as  bathed  in  blood,  and  will  contract  upon  receiving  a  slight 
stimulus;  in  fact  a  single  stimulus  will  often  call  forth  a  series  of  contractions 
of  the  ventricle.     The  frog's  ventricle,  when  its  muscular  and  nervous  con- 


Fic.  176. — Isolated  Nerve  Cells  from  the  Frog's  Heart.      /,  Usual  form;     //,  twin  cell;     C, 
capsule;    N,  nucleus;    P,  process.     (From  Ecker.) 


nections  with  the  auricle  are  physiologically  severed,  as  by  crushing,  will 
remain  quiet  when  fed  by  its  own  blood,  but  contracts  rhythmically  when 
fed  with  physiological  salt-solution. 

It  will  be  thus  seen  that  the  rhythmical  movements  appear  to  be  more 
marked  in  the  parts  supplied  by  the  ganglia,  that  ventricular  pieces  con- 
tract when  still  connected  with  the  auricles,  and  that  rhythmic  contractions 
of  the  ventricles  do  not  readily  occur  in  the  ordinary  condition  when  irri- 
gated with  blood.  These  are  regarded  as  facts  peculiarly  in  favor  of  the 
neurogenic  theory. 

The  Myogenic  Theory.  In  the  myogenic  theory  the  heart's  rhythmical 
contractions  are  explained  as  due  to  the  inherent  property  of  the  cardiac 
muscle  itself.  Most  convincing  facts  in  support  of  this  theory  have  been 
arrived  at  by  a  study  of  cardiac  muscle,  as  such,  and  by  studies  on  the 
whole  heart,  particularly  by  Gaskell's  method  of  blocking.  The  term 
blocking  is  explained  as  follows:  It  will  be  remembered  that  under  normal 
conditions  the  wave  of  the  contractions  in  the  heart  starts  at  the  sinus  and 
travels  down  over  the  auricles  to  the  ventricles,  the  irritability  of  the  muscle 


THEORIES    OF    THE    HEART-BEAT  177 

and  its  power  of  rhythmic  contractions  being  greatest  in  the  sinus,  less  in 
the  auricles,  and  least  in  the  ventricles.  By  an  arrangement  of  ligatures 
or  by  a  system  of  clamps,  one  part  of  the  heart  may  be  more  or  less  isolated 
from  any  other  portion.  With  such  a  clamp  the  contraction  waves  can  be 
more  or  less  completely  interrupted  in  their  passage  from  the  sinus  end  of 
the  heart  past  the  clamp  toward  the  ventricular  end.  If  the  clamp  is  com- 
plete, so  as  to  interrupt  the  physiological  continuity  between  the  parts,  then 
any  contractions  in  the  apical  portion  will  be  entirely  independent  of  those 
in  the  sino-auricular  portion.  If  the  blocking  is  partial  only,  then  the  ventric- 
ular end  of  the  heart  always  contracts  in  unison  with  the  sino-auricular, 
although  its  rate  may  be  as  i  to  i,  i  to  2,  1  to  3,  etc.  In  other  words,  only 
every  second  or  every  third  sino-auricular  contraction  will  be  able  to  pass 
the  block. 

The  effects  of  blocking  are  due  to  the  interruption  of  muscle  continuity 
rather  than  nerve  continuity.  This  is  beautifully  demonstrated  by  an  experi- 
ment of  zigzag  cutting  of  the  ventricle  in  the  terrapin,  since  it  cannot  be 
supposed  that  any  nerves  would  pass  through  the  ventricular  mass  by  such 
a  zigzag  course.  In  this  experiment  the  contraction  wave  passes  down 
over  the  muscle  and  around  the  end  of  the  cuts  until  it  reaches  the  apex, 
and  the  apex  contracts  in  sequence  with  the  auricle  and  base  of  the  ventricle. 
If  the  zigzag  cuts  are  made  almost  complete  so  as  to  reduce  to  a  minimum 
the  muscular  tissue  which  bridges  from  one  cut  to  the  next,  then  it  happens 
that  occasional  contractions  will  be  unable  to  pass  and  the  apex  contracts 
in  the  ratio  of  1  to  2,  or  1  to  3,  etc.,  as  described  above.  Thus,  division  of 
the  muscle  has  the  same  effect  as  partial  clamping  in  the  same  position. 

It  was  thought  for  a  long  time  that  in  the  mammal  there  is  no  mus- 
cular continuity  between  the  auricles  and  ventricles  to  conduct  the  contrac- 
tion wave,  but  a  well-marked  muscular  bridge,  the  bundle  of  His,  has  been 
shown  to  pass  between  these  two  parts.  This  fact  has  proven  to  be  of  strongest 
support  to  the  myogenic  theory.  Erlanger  has  recently  shown,  by  an  in- 
genious device  for  partially  clamping  this  muscular  band,  that  even  the 
mammalian  ventricle  exhibits  the  phenomenon  of  heart  block.  In  his  experi- 
ments the  ventricle  contracts  in  unison  with  every  auricular  contraction,  or 
only  every  second  or  every  third,  according  to  the  degree  of  blocking. 

It  was  shown  long  ago  that  the  isolated  apex  of  the  ventricle  of  the  frog 
remains  quiet  when  filled  with  blood,  but  readily  gives  good  rhythmic  con- 
tractions in  physiological  saline  and  other  artificial  solutions.  The  inac- 
tivity in  blood  is  not  necessarily,  therefore,  due  to  nervous  isolation  from 
the  ganglionated  parts  of  the  heart.  Contractions  occur  in  the  small  bits 
of  ventricular  muscle  as  isolated  by  Gaskell,  and  these  may  continue  for 
hours.  It  is  well  known  also  that  the  embryonic  heart  contracts  rhythmically 
before  nerve  cells  have  reached  the  organ. 

The  phenomena  of  heart  block,  the  contractions  of  the  ventricular  apex 
12 


178  THE    CIRCULATION     OF     THE    BLOOD 

when  physiologically  isolated  from  the  parts  of  the  heart  which  contain  the 
ganglia,  the  behavior  of  isolated  strips  of  the  heart,  especially  of  the  ventricle, 
and  the  rhythm  of  the  embryonic  heart  are  all  held  to  be  in  favor  of  the  myo- 
genic theory. 

Automaticity  of  the  Heart.  Whether  one  adopts  the  neurogenic 
or  myogenic  theory  of  the  heart's  beat,  he  has  still  to  explain  the  origin  of 
the  heart's  rhythm.  In  the  former  case  one  must  look  to  the  nervous 
apparatus  for  the  origin  of  the  rhythm;  in  the  latter  case,  the  muscular  ap- 
paratus, a  fact  to  which  Brown-Sequard  long  ago  called  attention.  In  the 
former  view  the  problem  is  to  explain  not  only  the  periodic  origin  of  the 
nerve  discharges  from  local  cardiac  ganglia,  but  also  to  explain  the  orderly 
discharge  of  nerve  impulses  which  maintains  the  proper  sequence  between 
sinus,  auricle,  and  ventricle. 

To  perhaps  the  majority  of  physiologists  the  facts  are  best  explained 
by  the  myogenic  theory.  The  origin  of  the  rhythm  is  here  supposed  to  be 
due  to  the  automatic  property  of  the  muscle  itself.  The  sequence  is  ex- 
plained on  the  observed  facts,  first,  that  muscular  contraction  in  cardiac 
muscle  is  conducted  throughout  the  continuity  of  the  mass,  and  second, 
the  most  highly  rhythmic  part  of  the  muscular  tissue  of  the  heart,  the  sinus, 
sets  the  rhythm  for  the  entire  heart. 

The  function  of  the  nervous  system,  by  this  view,  is  not  to  originate  the 
rhythm,  but  to  regulate  it,  the  detail  of  which  will  be  discussed  below. 

Relation  of  Rhythm  to  Nutrition.  The  whole  heart,  like  the 
muscular  parts  of  which  it  is  composed,  responds  delicately  to  its  condition 
of  nutrition.  In  the  frog's  and  turtle's  hearts  the  muscular  fibers  are  brought 
in  intimate  contact  with  the  blood  contained  within  its  cavities.  In  the 
mammalian  heart,  on  the  other  hand,  a  distinct  system  of  vessels,  the  coronary 
vessels  and  the  vessels  of  Thebesius,  supply  blood  to  the  organ.  If  the  heart 
is  supplied  with  nutrient  fluid  similar  to  its  normal  blood,  and  with  proper 
aeration  to  insure  plenty  of  oxygen,  it  contracts  with  a  strong  rhythm  for 
many  hours.  This  rhythm,  however,  responds  quickly  to  changes  in  the 
composition  of  the  nutrient  fluid.  An  abundant  supply  of  oxygen  is  absolutely 
necessary  to  the  maintenance  of  rhythm  in  the  mammalian  heart,  though  the 
heart,  especially  a  cold-blooded  heart,  will  contract  for  a  time  in  an  atmos- 
phere of  hydrogen.  No  doubt  the  organic  constituents  of  blood  are  very 
essential  to  the  prolonged  maintenance  of  rhythm  in  the  heart,  but  the  heart 
is  not  dependent  on  these  ingredients  for  its  immediate  reactions.  The  in- 
organic salts  seem  to  be  peculiarly  closely  related  to  the  development  and 
character  of  the  cardiac  rhythm,  figures  172  and  173.  Both  the  cold- 
blooded heart  and  the  mammalian  heart  respond  very  quickly  to  the  influ- 
ence of  these  salts.  The  details  of  this  influence  have  been  discussed  on 
page  173.  It  is  somewhat  surprising,  however,  that  the  highly  organfeed 
mammalian  heart  will  contract  rhythmically  for  hours  on  purely  inorganic 


INFLUENCE     OF    THE     CENTRAL    NERVOUS    SYSTEM 


179 


nutrient    fluid,    provided    only  that   the   oxygen   be   supplied   in   sufficient 
quantity  and  under  high  enough  tension. 

THE   REGULATIVE   INFLUENCE   OF   THE  CENTRAL  NERVOUS 
SYSTEM  ON  THE  HEART. 

The  heart  is  capable  of  automatic  rhythmic  movement,  yet  while  in  the 
body  its  beats  are  under  the  constant  control  of  the  central  nervous  system. 
The  influence  which  is  exerted  by  the  central  nervous  system  is  of  two  kinds: 
first,  in  the  direction  of  slowing  or  inhibiting  the  beats,  and,  second,  in  the 
direction  of  accelerating  or  augmenting  the  beats.  The  influence  of  the 
first  kind  is  brought  to  bear  upon  the  heart  through  the  fibers  of  the  pneumo- 
gastric  or  vagus  nerves,  and  that  of  the  second  kind  through  the  sympathetic 
nerves. 

The  Inhibitory  Nerves.  It  has  long  been  known,  indeed  ever 
since  the  experiments  of  the  Weber  brothers  in  1845,  that  stimulation  of  one 
or  both  vagi  produces  slowing  of  the  rhythm  of  the  heart.     It  has  since  been 


Fig.  177. — Effect  on  the  Heart  Rate  and  on  the  Arterial  Blood  Pressure  of  Stimulating  the 
Right  Vagus  of  the  Dog.  Stimulus  applied  at  the  mark  "on"  and  removed  at  "  off."  Pressure  in 
millimeters  of  mercury  shown  by  the  scale  to  the  left.  Time  in  seconds.  (New  figure  by  Hill  and 
Chilton.) 

shown,  in  all  of  the  higher  vertebrate  animals  experimented  with,  that  this 
is  the  normal  reaction  to  vagus  stimulation.  Moreover,  a  section  of  one 
vagus,  or  at  any  rate  of  both  vagi,  produces  acceleration  of  the  pulse;  and 
stimulation  of  the  distal  or  peripheral  end  of  the  divided  nerve  normally 
produces  slowing  or  stopping  of  the  heart's  beats. 


180 


THE    CIRCULATION     OF    THE     BLOOD 


It  appears  that  any  kind  of  stimulus,  either  chemical,  mechanical,  elec- 
trical, or  thermal,  produces  the  same  effect,  but  that  of  these  the  most  potent 
is  a  rapidly  interrupted  induction  current.  A  certain  amount  of  confusion 
has  arisen  as  to  the  effects  of  vagus  stimulation  in  consequence  of  the  fact 
that  fibers  of  the  sympathetic  nerve  run  within  the  trunk  of  the  vagus  nerves 
of  some  animals. 

The  result  of  stimulation  also  depends,  to  some  extent,  upon  the  exact 
position  of  the  application  of  the  stimulus.     Speaking  generally,  however, 


Fig.  178. — Tracing  Showing  Actions  of  the  Vagus  on  the  Heart  of  the  Frog.  Aur,  Auricular; 
vent,  ventricular  tracing.  The  part  between  perpendicular  lines  indicates  a  period  of  vagus  stimu- 
lation. C.  8  indicates  that  the  secondary  coil  was  8  cm.  from  the  primary.  The  part  of  tracing 
to  the  left  shows  the  regular  contractions  of  moderate  height  before  stimulation.  During  stimu- 
lation, and  for  some  time  after,  the  beats  of  auricle  and  ventricle  are  arrested.  After  they  com- 
mence again  they  are  single  at  first,  but  soon  acquire  a  much  greater  amplitude  than  before  the 
application  of  the  stimulus.      (After  Gaskell.) 

excitation  of  any  part  of  the  trunk  of  the  vagus  produces  inhibition,  the 
stimulus  being  particularly  potent  if  applied  to  the  points  where  the  nerves 
enter  the  substance  of  the  heart  at  the  situation  of  the  sinus  ganglia.  The 
stimulus  may  be  applied  to  either  vagus  with  like  effect. 

The  effect  of  the  stimulus  of  the  vagus  is  twofold — to  slow  the  rate,  or 
even  to  bring  the  heart  to  a  complete  standstill,  and  to  produce  a  decrease 


joMii»mi|i-Ulw 


Fig.  179. — Tracing  Showing  Diminished  Amplitude  and  Slowing  of  the  Pulsations  of  the  Auricle 
and  Ventricle  without  Complete  Stoppage  during  Stimulation  of  the  Vagus.      (After  Gaskell.) 

in  the  amplitude.  The  slowing  does  not  take  place  until  after  the  lapse  of 
a  short  latent  period  during  which  one  or  more  contractions  may  occur. 
The  stoppage  may  be  due  either  to  prolongation  of  the  diastole  or  to  diminu- 
tion of  the  systole.  Vagus  stimulation  inhibits  the  spontaneous  beats  of 
the  heart  only,  it  does  not  entirely  suppress  the  irritability  of  the  heart-muscle, 


THE    INHIBITORY    NERVES 


181 


since  mechanical  stimulation  may  bring  out  a  beat  during  the  pause  caused 
by  vagus  stimulation.  The  inhibition  of  the  beats  varies  in  duration  accord- 
ing to  the  strength  of  the  stimulus  and  the  animal  stimulated.  The  heart 
of  the  terrapin  can  be  completely  inhibited  for  hours  with  a  strong  stimulus. 
The  heart  of  a  dog  escapes  from  inhibition  in  a  few  seconds.  When  the 
beats  reappear,  the  first  few  are  usually  feeble,  and  may  be  auricular  only; 
after  a  time  the  contractions  become  more  and  more  strong,  and  very  soon 
exceed  both  in  amplitude  and  frequency  those  which  occurred  before  the 
application  of  the  stimulus.  This  phenomenon  is  shown  in  figure  178, 
which  illustrates  the  action  of  the  vagus  on  the  frog's  heart. 

The  inhibitory  fibers  have  their  origin  in  nerve  cells  in  the  motor  nucleus 
of  the  vagus  and  of  the  glosso-pharyngeal  located  in  the  floor  of  the  fourth 
ventricle.     These  cells  have  not  been  exactly  identified,  but  the  center  is 


_                                                            i_r                         —    '      — ■ -      ■■  - 

—=m                                                  ,,                              /?ate  13? 
-§  Rote,  w                             a/»WVV\aa/J^/V,   /JVWwia  /AW*  J^Vuu 

Aa^aAAAaa/\aAA     aAAAaaA/V^                       ^^ 

-=^**              \  a/v 

— =^zt               \\ 

=100 

n  m  »  n  )  m  m  n  n  m  m  m  >  i  n  1  m  >  n  1  1 1  r  n  rri 

Fig.  180. — Arterial  Blood  Pressure  of  the  Dog,  Showing  the  Effect  on  the  Heart  Rate  of  Cutting 
both  Vagus  Nerves  as  marked.  The  scale  to  the  left  shows  the  pressure  in  millimeters  of  mercury. 
Time  in  seconds.  The  momentary  inhibition  just  before  the  nerves  were  cut  is  probably  due  to 
mechanical  stimulation  of  the  nerves.      (New  figure  by   Hill  and  Chilton.) 


called  the  cardio-inhibitory  center.  The  center  is  a  bilateral  one  and  the 
fibers  from  it  pass  into  the  great  vagus  trunk  to  be  distributed  to  the  heart 
through  superior  and  inferior  cardiac  branches  which  help  to  form  the  cardiac 
plexus.  Within  the  heart  the  inhibitory  fibers  form  synapses  with  cells  whose 
axones  reach  the  cardiac  muscle  cells.  The  cardiac-inhibitory  center  is  in 
constant  tonic  activity,  and  the  tonic  influence  is  eliminated  when  both  nerves 
are  cut,  figure  180. 

The  center  is  also  influenced  by  afferent  impulses  which  may  reach  it 
from  the  heart  itself,  by  the  depressor  nerve,  or  from  other  parts  of  the  body. 
These  reflex  stimulations  of  the  heart  through  the  vagus  center  are  constantly 
occurring  during  our  daily  life  and  are  the  most  potent  factor  in  the  coordi- 
nations going  on  between  the  heart  and  the  rest  of  the  body. 

Rhythmical  alterations  of  the  heart  rate  occur  in  association  with  the 
effects  of  the  mechanical  variations  of  pressure  of  the  thorax  on  the  heart 
and  blood-vessels.     Apparently  the  cardio-inhibitory  center    is    stimulated 


182 


THE    CIRCULATION     OF    THE    BLOOD 


during  the  fall  of  blood  pressure.  The  activity  of  the  center  produces  a 
slower  rate  of  the  heart  during  expiration,  shown  in  figure  241.  This  vari- 
ation in  heart  rate  disappears  when  the  vagi  are  cut  off  from  the  center. 


Fig.  181. — Diagrammatic  Representation  of  the  Origin  and  Course  of  the  Cardiac  Nerves  in 
the  Dog.  Vag.  Syn,  Vago-sympathetic  nerve;  Dl,  D&,  first  to  fifth  dorsal  spinal  nerves.  In- 
hibitory fibers  in  red,  accelerators  in  black.    (Modified  from  Moret.) 


The  Accelerator  Nerves.  The  influence  of  the  accelerator  nerves 
reaching  the  heart  through  the  sympathetic  is  the  reverse  of  that  of  the  vagus. 
Stimulation  of  the  sympathetic,  even  of  one  side,  produces  acceleration  of 
the  rate  of  the  heart-beats,  and,  according  to  certain  observers,  section  of  the 
nerve  produces  slowing.  The  acceleration  produced  by  stimulation  of  the 
sympathetic  fibers  is  accompanied  by  increased  force,  and  so  the  action  of 
the  nerve  is  more  properly  termed  angmentor.  The  sympathetic  differs 
from  the  vagus  in  several  particulars  other  than  the  augmentation  which  it 
produces;    first,  the  stimulus  required  to  produce  any  effect  must  be  more 


THE     ACCELERATOR    NERVES  183 

powerful  than  is  the  case  with  the  vagus  stimulation;  second,  a  longer  time 
elapses  before  the  effect  is  manifest;  and  third,  the  augmentation  is  followed 
by  exhaustion,  the  beats  being  after  a  time  feeble  and  less  frequent.  The 
stimulation  of  the  vago-sympathetic  in  the  frog,  which  usually  produces 
inhibition,  will  occasionally  produce  acceleration,  especially  if  the  heart  is 
beating  feebly  at  the  time  of  the  stimulation. 

The  fibers  of  the  sympathetic  system,  which  influence  the  heart-beat  in 
the  frog,  leave  the  spinal  cord  by  the  anterior  root  of  the  third  spinal  nerve. 
They  pass  by  the  ramus  communicans  to  the  third  sympathetic  ganglion, 
thence  to  the  second  ganglion,  the  annulus  of  Vieussens  (around  the 
subclavian  artery),  through  the  first  ganglion,  and  along  the  main  trunk 
of  the  sympathetic  to  near  the  exit  of  the  vagus  from  the  cranium.  There 
the  two  nerves  join  and  run  down  to  the  heart  within  a  common  sheath, 
forming  the  vago-sympathetic  trunk. 

In  the  dog  the  augmentor  fibers  leave  the  cord  by  the  anterior  roots  of 
the  second  and  third  dorsal  nerves,  and  possibly  also  by  the  first,  fourth, 
and  fifth  dorsal  nerves.  They  pass  by  the  rami  communicantes  to  the  gan- 
glion stellatum,  or  first  thoracic  ganglion,  around  the  annulus  of  Vieussens 
to  the  inferior  cervical  ganglion  of  the  sympathetic.  Fibers  from  the  annulus 
or  from  the  inferior  cervical  ganglion  proceed  to  the  heart,  figure  181.  The 
course  of  the  augmentor  fibers  in  the  spinal  cord  is  not  so  well  known  except 
that  they  originate  in  an  augmentor  center  in  the  medulla.  The  circulation 
of  venous  blood  appears  to  stimulate  the  augmentor  center,  and  of  highly 
oxygenated  blood  the  inhibitory  center. 

The  accelerator  center,  like  the  inhibitory,  is  in  constant  tonic  activity; 
and  the  cardiac  acceleration  on  cutting  the  vagi,  shown  in  figure  180,  is  in 
part  to  be  ascribed  to  this  tone.  When  both  nerves  are  stimulated  together, 
the  resulting  rate  is  the  algebraic  sum  of  the  opposed  influences,  according 
to  Hunt.  The  accelerator  center  is  influenced  by  afferent  impulses  arising 
throughout  the  body,  and  these  reflexes  contribute  to  the  general  coordina- 
tion of  the  chest  with  the  activities  of  the  body. 

In  addition  to  direct  and  reflex  stimulation,  impulses  passing  down  from 
the  cerebrum  may  have  a  similar  effect. 

Other  Influences  Which  Affect  the  Heart.  A  great  variety  of  spe- 
cial conditions  influence  the  heart's  action  in  the  normal  body,  conditions 
that  are  not  discussed  directly  under  any  of  the  categories  treated  above. 
Of  these  may  be  mentioned  the  coronary  circulation,  temperature,  mechanical 
tension,  age,  sex,  etc. 

The  Coronary  Circulation.  The  contractions  of  the  heart  cannot  long 
be  maintained  without  a  due  supply  of  blood  or  other  nutrient  fluid.  The 
nutrient  fluid  for  the  heart  of  man  and  the  mammals  is  supplied  from  the 
coronary  arteries  and  the  vessels  of  Thebesius.  The  coronary  arteries  arise 
from  the  base  of  the  aorta,  where  they  receive  the  benefit  of  the  highest  arterial 


184  THE    CIRCULATION    OF    THE    BLOOD 

pressure.  The  coronary  arteries  are  terminal  arteries;  that  is,  they  do  not 
permit  the  establishment  of  a  collateral  circulation  when  one  of  their  branches 
is  blocked.  If  the  block  be  complete,  that  portion  of  the  heart  wall  supplied 
by  the  branch  dies.  The  immediate  effect  of  the  closure  of  a  large  coronary 
branch,  in  the  dog,  may  be  occasional  and  transient  irregularity,  or  arrest 
of  the  ventricular  contractions  preceded  by  irregularities  in  the  force  of  the 
contractions  and  a  diminution  in  the  amount  of  work  performed.  The 
force,  rather  than  the  rate,  of  the  ventricular  contractions  is  closely  dependent 
upon  the  blood  supply  to  the  coronary  arteries.  Porter  and  others  have 
shown  that  the  pressure  in  the  coronary  vessels  follows  closely  the  pressure 
in  the  aorta  and  that  there  is  not,  as  formerly  claimed,  a  closure  of  these 
vessels  by  the  pressure  of  the  systole  of  the  ventricle. 

The  vessels  of  Thebesius,  which  have  been  demonstrated  to  open  both 
into  the  auricular  and  ventricular  cavities,  must  now  be  looked  upon,  ac- 
cording to  the  investigations  of  Pratt,  as  an  important  source  of  cardiac 
nutrition.  Blood  may  pass  through  them  by  way  of  connecting  branches 
to  the  coronary  arteries  and  veins.  Pratt  succeeded  in  maintaining  cardiac 
contractions  for  several  hours  when  the  only  source  of  nutrition  was  from 
these  vessels.  This  source  of  nutrition  may  account  for  the  survival  of 
hearts  for  years  where  pronounced  arterio-sclerosis  of  the  coronary  arteries 
exists. 

Alteration  oj  Temperature.  The  effect  of  cold  is  to  slow  the  rate  of  the 
heart-beat,  and  if  the  heart  of  a  frog  be  cooled  down  to  o°  C.  it  will  stop  beat- 
ing. It  is  said  that  the  frog's  heart  may  be  frozen,  and  when  thawed  will 
renew  its  spontaneous  beats.  The  effect  of  heat  is  to  quicken  and  shorten 
the  heart-beats,  but  at  a  moderate  temperature,  200  C,  the  contractions  are 
increased  in  force. 

The  isolated  mammalian  heart  is  influenced  by  temperature  variations 
in  much  the  same  way  as  that  of  the  frog.  It  will  contract  slowly  in  a  low 
temperature  and  rapidly  in  a  temperature  higher  than  that  normal  to  the 
body.  The  very  rapid  heart  in  some  high  fevers  is  in  part  due  to  the  in- 
crease in  temperatures  which  affects  the  heart  directly. 

Mechanical  Tension.  The  mechanical  factors  produced  by  the  heart 
beat  are  so  prominent  that  it  would  be  surprising  indeed  if  there  were  no 
reaction  of  these  mechanical  conditions  on  the  heart  itself.  The  isolated 
cardiac  muscle  responds  very  quickly  to  variations  in  tension.  Beginning 
with  a  low  tension  the  activity  of  heart  muscle  is  increased  up  to  a  certain 
optimum  tension,  after  which  further  increase  is  unfavorable  to  the  develop- 
ment of  automatic  rhythm.     A  quite  strong  stretching  will  paralyze  the  muscle. 

Tension  on  the  whole  heart  influences  its  activity,  not  only  through  the 
effects  on  the  muscle,  but  indirectly  through  the  nervous  mechanism.  High 
tension,  such  as  contracting  against  a  high  aortic  pressure,  stimulates  sensory 
nerves  of  the  heart  which,  acting  through  the  depressor  nerve  on  the  inhibitory 


OTHER     INFLUENCES    WHICH    AFFECT    THE     HEART  185 

center,  produce  reflex  slowing  of  the  heart,  as  well  as  reflex  vaso-dilatation, 
both  of  which  relieve  the  high  tension.  This  nerve  reaction  takes  place  with 
a  tension  which  still  mechanically  stimulates  the  cardiac-muscle  substance, 
and  the  inhibitory  effects  must  therefore  first  overcome  the  direct  stimulating 
effect  of  the  tension  on  the  muscle  fibers. 

Age,  Sex,  etc.  The  average  heart  rate  for  the  normal  adult  man  is  72 
times  a  minute,  but  this  rate  will  vary  much  in  different  individuals  accord- 
ing to  the  age,  sex,  size,  and  personal  equation.  The  frequency  of  the  heart's 
action  gradually  diminishes  from  the  commencement  to  near  the  end  of  life, 
but  is  said  to  increase  again  somewhat  in  extreme  old  age,  thus: 

Before  birth  the  average  number  of  pulsations  per  minute  is 150 

Just  after  birth 130  to  140 

During  the  first  year 115  to  130 

During  the  second  year 100  to  1 15 

During  the  third  year 90  to  100 

About  the  seventh  year 85  to  90 

About  the  fourteenth  year 80  to  85 

In  adult  age 70  to  80 

In  old  age 60  to  70 

In  decrepitude 65  to  75 

The  heart  rate  is  greater  in  woman  than  in  man.  It  is  also  greater  in 
small  than  in  large  individuals.  The  rate  varies  from  the  type  in  certain 
individuals  where  no  cause  can  be  assigned  other  than  personal  equation. 

Poisons  and  Other  Chemical  Substances.  A  large  number  of  chemical 
substances  have  a  distinct  effect  upon  the  cardiac  contractions.  Of  these 
the  most  important  are  atropine,  muscarine,  digitalis,  barium,  etc. 


J8C 


/40 
/20 
100 

80 


Fig.  182. — The  Effect  of  an  Intravenous  Injection  of  Atropine  on  the  Dog's  Heart  Rate  Meas- 
ured by  Means  of  a  Blood-Pressure  Curve.     (New  figure  by  Doolev.) 

Atropine  produces  considerable  augmentation  of  the  heart-rate,  and 
when  acting  upon  the  heart  prevents  inhibition  by  vagus  stimulation.  Its 
effects  are  produced  by  poisoning  the  nerve  endings  of  the  vagus  within 


186  THE    CIRCULATION    OF    THE    BLOOD 

the  heart.  With  these  endings  poisoned,  stimuli  arising  in  the  inhibitory 
center  of  the  medulla  (tonic  activity),  or  artifically  applied  to  the  vagus, 
cannot  reach  the  heart  muscle,  and  inhibition  is  impossible. 

Muscarine,  which  is  obtained  from  various  species  of  poisonous  fungi, 
produces  marked  slowing  of  the  heart-beats,  and,  in  larger  doses,  stoppage 
of  the  heart.  It  produces  an  effect  similar  to  that  of  prolonged  vagus  stimu- 
lation. The  effect  can  be  removed  by  the  action  of  atropine,  hence  is 
supposed  to  stimulate  the  nerve  endings  of  the  vagus. 

Digitalis  slows  the  heart  by  stimulating  the  vagi  at  their  origin  in  the 
inhibitory  center  in  the  medulla.  The  heart  muscle  itself  is  also  rendered 
more  excitable. 

Veratrine  and  aconitine  have  a  somewhat  similar  effect. 

THE  CIRCULATION  THROUGH  THE  BLOOD-VESSELS. 

Blood  Pressure.  The  subject  of  blood  pressure  has  been  already 
incidentally  mentioned  more  than  once  in  the  preceding  pages;  the  time  has 
now  arrived  for  it  to  receive  more  detailed  consideration. 

That  the  blood  exercises  pressure  upon  the  walls  of  the  vessels  containing 
it  is  due  to  the  following  facts: 

The  heart  at  each  contraction  forcibly  injects  a  considerable  amount  of 
blood,  80  to  100  c.c,  suddenly  and  quickly  into  the  arteries. 

The  arteries  are  highly  distensible  and  stretch  to  accommodate  the  extra 
amount  of  blood  forced  into  them.  The  arteries  are  already  full  of  blood 
at  the  commencement  of  the  ventricular  systole,  since  there  is  not  sufficient 
time  between  the  heart-beats  for  the  blood  to  pass  into  the  veins. 

There  is  a  distinct  resistance  interposed  to  the  passage  of  the  blood  from 
the  arteries  into  the  veins  by  the  enormous  number  of  minute  vessels,  small 
arteries  (arterioles)  and  capillaries,  into  which  the  main  artery  has  been 
ultimately  broken  up.  The  sectional  area  of  the  capillaries  is  several  hundred 
times  that  of  the  aorta,  and  the  friction  generated  by  the  passage  of  the  blood 
through  these  minute  channels  opposes  a  considerable  hindrance  or  resistance 
in  its  course.  The  resistance  thus  set  up  is  called  peripheral  resistance. 
The  friction  is  greater  in  the  arterioles,  where  the  current  is  comparatively 
rapid,  than  in  the  capillaries,  where  it  is  slow. 

The  interaction  of  these  factors — heart-beat,  elastic  vessels,  and  periph- 
eral resistance — is  sufficient  to  maintain  a  continuous  flow  of  blood  through 
the  entire  circulatory  system.  It  is  the  interrelation  of  these  factors  which 
maintains  an  even  and  steady  flow  through  the  capillaries  and  past  the  tissues, 
where  it  is  desirable  that  the  conditions  of  blood  flow  should  be  most  con- 
stant. In  fact,  we  shall  find  that  it  is  through  the  interaction  of  this  same 
group  of  factors,  together  with  the  possibility  of  variations  through  the  regu- 
lation of  their  nerve-motor  mechanisms,  that  we  have  the  great  variations 


ARTERIAL     BLOOD     PRESSURE  187 

and  adjustments  of  blood  pressure,  speed  of  flow,  volume  of  flow,  and  the 
regulation  of  volume  in  particular  parts  of  the  body. 

Arterial  Blood  Pressure.  That  the  blood  exerts  considerable  pres- 
sure upon  the  arterial  walls  in  keeping  them  in  a  stretched  or  distended 
condition  may  be  readily  shown  by  puncturing  any  artery;  the  blood  is 
instantly  projected  with  great  force  through  the  opening,  and  the  jet  rises  to 
a  considerable  height,  the  exact  level  of  which  varies  with  the  size  of  the  artery 
experimented  upon.  If  a  large  artery  be  punctured  the  blood  may  be  pro- 
jected upward  for  several  feet,  whereas  if  it  is  a  small  artery  the  jet  does  not 
rise  so  high.  Another  characteristic  of  the  jet  of  blood  from  a  cut  artery, 
particularly  well  marked  if  the  vessel  be  a  large  one  and  near  the  heart,  is  the 
intermittent  character  of  the  outflow.  If  the  artery  be  cut  across,  the  jet 
issues  with  force,  chiefly  from  the  central  end.  If  there  is  considerable 
anastomosis  of  vessels  in  the  neighborhood  the  jet  from  the  peripheral  end 
may  be  as  forcible  and  as  intermittent  as  that  from  the  central  end.  The 
intermittent  flow  in  the  arteries  which  is  due  to  the  action  of  the  heart,  and 
which  represents  the  systolic  and  diastolic  alterations  of  blood  pressure, 
may  be  felt  if  the  finger  be  placed  upon  a  sufficiently  superficial  artery.  The 
finger  is  apparently  raised  and  lowered  by  the  intermittent  distention  of  the 
vessel  occurring  at  each  heart-beat.  This  intermittent  distention  of  the 
artery  is  what  is  known  as  the  Pulse,  to  the  further  consideration  of  which 
we  shall  presently  return,  but  we  may  say  here  that  in  the  normal  condition 
the  pulse  is  a  characteristic  of  the  arterial,  and  is  absent  from  the  venous,  flow. 

At  the  same  time  it  must  be  recollected  that  in  the  veins  also  the  blood 
exercises  a  pressure  on  its  containing  vessel  which  is  small  when  compared 
with  the  arterial  pressure.  As  might  be  expected,  therefore,  the  blood  is 
not  expelled  with  so  much  force  if  a  vein  be  punctured  or  cut.  The  flow 
from  the  cut  vein  is  continuous  and  not  intermittent,  and  the  greater  amount 
of  blood  comes  from  the  peripheral  and  not  from  the  central  end,  as  is  the 
case  when  an  artery  is  severed. 

Methods  of  Measuring  Arterial  Blood  Pressure.  The  pressure  in 
an  artery  may  be  measured  by  cutting  the  vessel  and  introducing  into  it  a 
glass  tube  which  has  a  tall  vertical  limb.  A  column  of  blood  will  rise  in  the 
tube  at  once  to  the  height  that  can  be  supported  by  the  pressure  in  that  par- 
ticular vessel.  If  the  vessel  be  an  artery,  the  blood  will  rise  several  feet, 
according  to  the  distance  of  the  vessel  from  the  heart,  and  when  it  has  reached 
its  highest  point  it  will  be  seen  to  oscillate  with  the  heart-beats.  This  ex- 
periment shows  that  the  pressure  which  the  blood  exerts  upon  the  walls  of 
the  contained  artery  equals  the  pressure  of  a  column  of  blood  of  a  certain 
height.  In  the  case  of  the  rabbit's  carotid  it  is  equal  to  90  to  120  cm.  of  blood, 
or  rather  more  than  the  same  height  of  water.  In  the  case  of  the  vein,  if  a 
similar  experiment  be  performed,  blood  will  rise  in  the  tube  only  for  8  or 
10  cm.  or  less. 


188  THE     CIRCULATION     OF    THE    BLOOD 

The  usual  method  of  estimating  the  amount  of  blood  pressure  differs 
somewhat  from  the  foregoing  simple  experiment.  Instead  of  a  simple  straight 
tube  of  glass  inserted  into  the  vessel,  a  U-shaped  tube  containing  mercury, 
the  mercurial  manometer,  is  employed.  The  artery  is  connected  with  the 
manometer  by  means  of  a  small  cannula  which  is  inserted  into  the  vessel, 
an  arrangement  being  made  whereby  the  cannula,  tubes,  etc.,  are  filled  with 
a  saturated  saline  solution  to  prevent  the  clotting  of  blood  when  it  is  allowed 


Fig.  183. — Diagram  of  Ludwig's  Kymograph  and  Mercurial  Manometer.  A,  Revolving  cylin- 
der, worked  by  a  clock-work  arrangement  contained  in  the  box  (S),  the  speed  being  regulated  by  a 
fan  above  the  box;  cylinder  supported  by  an  upright  (b),  and  capable  of  being  raised  or  lowered 
by  a  screw  (a),  by  a  handle  attached  to  it;  D,  C,  E,  represent  a  mercurial  manometer,  a  somewhat 
different  form  of  which  is  shown  in  the  next  figure. 

to  pass  from  the  artery  into  the  apparatus.  The  loss  of  blood  is  prevented 
during  the  preparation  of  the  details  of  the  experiment  by  a  clamp  or  bull- 
dog forceps.  The  free  end  of  the  U-tube  of  mercury  contains  a  very  fine 
glass  or  metal  rod  with  a  bulb  which  floats  upon  the  surface  of  the  mercury 
and  oscillates  with  the  oscillations  of  the  mercury.  As  soon  as  there  is  free 
communication  between  the  artery  and  the  tube  of  mercury,  the  blood  rushes 
out  and  pushes  before  it  the  column  of  mercury.  The  mercury  will  there- 
fore rise  in  the  free  limb  of  the  tube,  and  will  continue  to  do  so  until  a  point 
is  reached  which  corresponds  to  the  mean  pressure  of  the  blood-vessel  used. 
The  blood  pressure  is  thus  communicated  to  one  limb  of  the  mercurial  column; 


METHODS     OF     MEASURING     ARTERIAL     BLOOD     PRESSURE 


189 


and  the  depth  to  which  the  latter  sinks,  added  to  the  height  to  which  it  rises 
in  the  other  limb,  the  weight  of  the  saline  solution  being  substracted,  will 
give  the  height  of  the  mercurial  column  which  the  blood  pressure  balances. 
For  the  estimation  of  the  amount  of  blood  pressure  at  any  given  moment, 
no  further  apparatus  than  this  is  necessary;  but  for  accurately  noting  the 
variations  of  pressure  in  the  arterial  system,  as  well  as  its  absolute  amount, 
the  instrument  is  usually  combined  with  a  recording  apparatus,  called  a 
kymograph,  figure  183,  and  permanent  records  are  made  of  the  observations. 
The  recording  apparatus  consists  of  a  revolving  cylinder,  figure  183,  A, 
which  is  moved  by  clock-work,  and  the  speed  of  which  is  capable  of  regula- 
tion. The  cylinder  is  covered  with  glazed  paper,  blackened  in  the  flame 
of  a  lamp,  and  the  mercurial  manometer  is  so  fixed,  figure  183,  D,  that  its 


Fig.  184. — Ludwig's  Mercury  Manometer.  The  manometer  is  shown  in  figure  183,  D,  C,  E. 
The  mercury  which  partially  fills  the  tube  supports  a  float  in  the  form  of  a  piston,  nearly  filling  the 
tube;  a  wire  is  fixed  to  the  float,  and  the  writing  style  or  pen  is  guided  by  passing  through  the  brass 
cap  of  the  manometer  tube ;  the  pressure  is  communicated  to  the  mercury  by  means  of  a  flexible 
metal  tube  filled  with  fluid. 


float,  provided  with  a  style,  writes  on  the  cylinder  as  it  revolves.  There  are 
many  ways  in  which  the  mercurial  manometer  may  be  varied;  in  figure  184 
is  seen  a  form  which  is  known  as  Ludwig's.  In  order  to  obviate  the  necessity 
of  a  large  quantity  of  blood  entering  the  tube  of  the  apparatus,  it  is  usual  to 
have  some  arrangement  by  means  of  which  the  mercury  may  be  made  to 
rise  in  the  tube  of  the  manometer  to  the  level  corresponding  to  approxi- 
mately the  mean  pressure  of  the  artery  experimented  with,  so  that  the  writing 
style  simply  records  the  variations  of  the  blood  pressure  above  and  below 
the  mean  pressure.  This  is  done  by  causing  the  saline  solution,  generally 
a  saturated  solution  of  sodium  carbonate  or  a  10  per  cent  magnesium  sul- 


190 


THE     CIRCULATION    OF    THE     BLOOD 


phate,  to  till  the  apparatus  from  a  bottle  suspended  at  a  height  about  that 
of  the  pressure  to  be  measured,  and  capable  of  being  raised  or  lowered  as 
required  for  the  purpose.  The  cannula  inserted  and  tied  into  the  artery 
may  be  of  several  different  kinds.     A  glass  T-tube  with  the  end  drawn  out 


Fig.  185. — Arterial  Cannula.     T-form  for  convenience  in  washing  out  clots. 

and  cut  so  that  it  is  oblique,  and  provided  with  a  slightly  constricted  neck 
to  prevent  its  coming  out  of  the  artery  easily,  is  a  very  convenient  form, 
figure  185.  Of  the  two  free  ends  of  the  T-cannula  one  is  connected  with  the 
manometer,  the  other  with  the  pressure  bottle.     The  peripheral  end  of  the 


"t*i«iiitt*ttiti**iiit-ttt  *  t*-*-*  t-*-*  *  i  t  **  ft-*-* 

Fig.  186. — Tracing  of  Normal  Arterial  Pressure  in  the  Dog,  Obtained  with  the  Mercurial  Man- 
ometer. The  smaller  undulations  correspond  with  the  heart-beats;  the  larger  curves  with  the  re- 
spiratory movements.  Pressure  is  in  millimeters  of  mercury  as  shown  by  the  scale  to  the  left. 
Time  in  seconds.     (New  figure  by  March  and  Nugent.) 

cut  artery  is  tied  to  obviate  the  escape  of  blood.  By  this  means,  the  pressure 
communicated  to  the  column  of  mercury  is  the  forward,  and  not  the  lateral, 
pressure  of  blood,  but  there  is  very  little  difference. 

As  soon  as  the  experiment  is  begun,  the  writing  float  is  seen  to  oscillate 


METHODS     OF    MEASURING     ARTERIAL     BLOOD     PRESSURE 


191 


in  a  regular  manner,  and  a  curve  of  blood  pressure  is  traced  upon  the  smoked 
paper  by  the  style  (or,  if  a  continuous  roll  of  unsmoked  paper  be  used,  the 
trace  is  made  by  an  inked  pen)  when  a  figure  similar  to  figure  186  will  be 
obtained.  This  indicates  two  main  variations  of  the  blood  pressure.  The 
smaller  excursions  of  the  lever  correspond  with  the  systole  and  diastole  of  the 
heart,  and  the  larger  curves  correspond  with  the  respirations,  being  called 
the  respiratory  undulations  of  blood  pressure,  to  which  attention  will  be  directed 
in  the  next  chapter.  Of  course,  the  undulations  spoken  of  are  seen  only  in 
records  of  arterial  blood  pressure.  They  are  more  clearly  marked  in  the  ar- 
teries nearer  the  heart  than  in  those  more  remote.  The  amount  of  the 
pressure  in  the  smaller  arteries  as  well  as  the  indication  of  the  systolic  rise 
of  pressure  is,  comparatively  speaking,  small. 

In  order  to  record  the  details  of  the  undulations  of  arterial  pressure,  it  is 
better  for  some  purposes  to  use  the  Hiirthle  membrane  manometer  than  the 
mercurial  manometer.     Two  views  of  this  instrument  are  shown  in  figure  166. 


Fig.  187. — Tracing  of  Normal  Arterial  Pressure  Taken  from  the  Rabbit  with  a  Hiirthle  Manom- 
eter.    The  horizontal  lines  show  zero  pressure.     Time  in  seconds.     (Dreyer.) 


The  instrument  consists  of  a  hollow  tube  and  cup  covered  with  rubber  sheet 
against  which  a  disc  supported  by  a  metal  spring  is  adjusted.  The  apparatus 
is  filled  with  fluid,  the  interior  of  which  is  connected  with  the  artery  by  means 
of  a  metal  tube  and  cannula.  The  pressure  transmitted  to  the  apparatus 
tends  to  stretch  the  rubber  and  bend  the  spring,  and  the  movement  thus 
produced  is  communicated  by  means  of  a  lever  to  a  writing  style  and  so  to 
a  recording  apparatus.  This  instrument  obviates  the  errors  which  might 
be  caused  by  the  inertia  of  the  mercury  in  the  mercurial  manometer;  it  also 
shows  in  more  detail  the  variations  of  the  blood  pressure  in  the  vessel  during 
and  after  each  individual  beat  of  the  heart. 

As  regards  the  actual  amount  of  blood  pressure,  from  observations  which 
have  been  made  by  means  of  the  mercurial  manometer,  it  has  been  found 


192 


THE     CIRCULATION     OF    THE     BLOOD 


that  the  pressure  of  blood  in  the  carotid  of  a  rabbit  is  capable  of  supporting 
a  column  of  90  to  120  mm.  of  mercury;  in  the  dog  100  to  175  mm.;  in  the 
horse  152  to  200  mm.;  and  in  man  the  pressure  is  estimated  to  be  about  the 
same  as  in  the  horse.  To  measure  the  absolute  amount  of  this  pressure 
in  any  artery  multiply  the  area  of  its  transverse  section  by  the  height 
of  the  column  of  mercury  which  is  already  known  to  be  supported 
by  the  blood  pressure  in  any  part  of  the  arterial  system.  The  weight  of  a 
column  of  mercury  thus  found  will  represent  the  absolute  pressure  of  the 
blood.  Calculated  in  this  way,  the  blood  pressure  in  the  human  aorta  is 
equal  to  1.93  kilogrammeters;  that  in  the  aorta  of  the  horse  being  5.2  kilo- 
grammeters;  and  that  in  the  radial  artery  at  the  human  wrist  only  0.08 
kilogrammeter.  Supposing  the  muscular  power  of  the  right  ventricle  to  be 
only  one-fourth  that  of  the  left,  the  blood  pressure  in  the  pulmonary  artery 
will  be  only  0.5  kilogrammeter.  The  amounts  above  stated  represent  the 
arterial  tension  at  the  time  of  the  ventricular  contraction. 

The  arterial  pressure  is  greatest  at  the  beginning  of  the  aorta,  and  de- 
creases toward  the  capillaries.  It  is  greatest  in  the  arteries  at  the  period  of 
the  ventricular  systole,  and  least  during  the  diastole.  The  blood  pressure 
gradually  lessens  as  we  proceed  from  the  arteries  near  the  heart  to  those  more 
remote,  and  again  from  these  to  the  capillaries,  as  it  does,  also,  from  the 
capillaries  along  the  veins  to  the  right  auricle. 

Arterial  Blood  Pressure  Measurements  in  Man.  A  number  of 
instruments  have  been  devised  for  estimating  blood  pressure  in  man  for 


Fig.  188. — Riva-Rocci  Apparatus  (schematic)  for  Determining  Blood  Pressure  in  Man. 


PRESSURE     MEASUREMENTS     IN     MAN 


103 


clinical  purposes.  Some  of  these,  though  excellent  in  principle,  are  too  com- 
plicated for  general  use.  The  first  simple  and  approximately  accurate  form 
of  apparatus  was  that  devised  by  Riva-Rocci  in  1896.     This  has  been  modi- 


Fig.  189. — Erlanger's  Sphygmomanometer,  Shown  with  the  Rubber  Bag  Attached  to  the  Arm. 
The  picture  is  taken  at  the  end  of  an  experiment  after  the  pressure  in  the  instrument  is  run  up  again 
to  above  the  systolic  pressure.  The  upper  part  of  the  cylinder  shows  a  sphygmogram  taken  with 
the  instrument.     (Experiment  and  photo  by  Hill  and  Watkins.) 

fied  and  improved  in  minor  points  since,  but  the  principles  of  the  original 
instrument  remain  practically  the  same. 

In  brief,  the  apparatus,  figure  188,  consists  of  an  elastic  tube  ending  in 
a  rubber  bag  which  can  be  adjusted  about  the  arm  or  forearm,  and  a  mercury 
manometer  connected  with  this  tube  and  also  with  some  form  of  air  pump 
used  for  inflating  the  tube  about  the  arm  and  thus  exerting  pressure  upon 
its  blood-vessels.  The  elastic  tube  is  covered  by  some  inelastic  tissue,  usually 
a  leather  cuff,  in  order  that  the  inflation  of  the  bag  may  cause  the  full  increase 
of  pressure  to  be  exerted  upon  the  encased  arm.  By  inflating  the  bag  until 
the  pulse  at  the  wrist  just  disappears,  and  reading  the  height  of  the  column 
of  mercury  in  the  manometer,  the  maximum  or  systolic  pressure  is  obtained 
13 


194  The   circulation   of   the   blood 

in  millimeters  of  mercury.  If  now  the  pressure  on  the  arm  is  reduced  until 
the  widest  oscillations  of  the  mercury  column  are  obtained,  the  lowest  position 
of  the  mercury  meniscus  represents  the  diastolic  pressure. 

The  apparatus  depends  on  the  principle  that  an  external  pressure  just 
equal  to  the  maximal  pressure  within  an  artery  will  hold  the  vessel  in  the 
collapsed  condition,  a  fact  that  has  been  proven  for  vessels  that  are  exposed. 
An  external  pressure  that  will  just  equal  the  minimal  or  diastolic  pressure 
will  cause  a  complete  collapse  of  a  vessel  during  diastole  and  will  allow  a 
complete  expansion  of  an  artery  to  it;  maximal  limits  during  the  systolic 
period  of  pressure.  In  other  words,  the  mercury  of  the  manometer  will 
oscillate  to  its  maximal.  If  the  pressure  is  reduced  to  a  still  lower  point,  it 
will  not  be  sufficient  to  compress  the  artery  completely,  and  the  mercury 
oscillations  will  again  become  smaller.     In  applying  the  instrument  to  the 


Fig.  190. — Tracing  taken  with  Erlanger's  Sphygmomanometer.  The  figures  indicate  pres- 
sure in  millimeters  of  mercury.   Systolic  pressure,  160;  diastolic  pressure,  120.   (New  figure  by  Hill.) 

brachial  artery,  one  must,  of  course,  deal  with  a  vessel  deeply  buried  in  mus- 
cular and  other  tissues.  These  latter  tissues  probably  consume  a  certain 
small  percentage  of  the  pressure,  an  error  which  may  be  ignored  for  all  com- 
parative purposes. 

Erlanger  has  perfected  a  form  of  sphygmomanometer  which  contains  a 
very  ingenious  and  compactly  arranged  recording  device,  figure  189.  This 
instrument  has  a  mercury  manometer  from  which  the  pressures  are  read  off 
directly.  On  a  side  limb  of  the  manometer  there  is  a  rubber  bag  enclosed 
in  a  glass  bell.  The  cavity  of  the  bell  outside  of  the  rubber  bag  is  connected 
with  a  recording  tambour,  the  entire  apparatus  being  fully  supplied  with 
the  necessary  valves  and  adjusting  devices  which  make  it  mechanically  very 
perfect.  The  instrument  is  mounted  on  a  stand  with  a  small  clock  and 
recording  cylinder  adapting  it  to  convenient  clinical  use. 

The  brachial  arterial  pressure  of  man  when  taken  by  this  form  of  appara- 
tus has  been  found  to  vary  greatly,  but  Erlanger  gives  no  mm.  of  mercury 
as  the  average  of  observations  on  voung  adults  in  the  determination  of  the 


VENOUS    BLOOD     PRESSURE    AND    CAPILLARY    PRESSURE  195 

systolic  pressure,  i.e.,  the  maximal  arterial  pressure.  He  gives  for  the  dias- 
tolic pressure  40  to  45  mm.  of  mercury  below  the  systolic  pressure.  Other 
observers  using  the  same  method  find  a  somewhat  higher  average  pressure, 
see  figure  190,  which  represents  a  fair  type  of  observation. 

The  Venous  Blood  Pressure  and  Capillary  Pressure.  The  blood 
pressure  in  the  veins  is  nowhere  very  great,  but  is  greatest  in  the  small  veins, 
while  in  the  large  veins  near  the  heart  the  pressure  may  become  negative,  or, 
in  other  words,  when  a  vein  is  put  in  connection  with  a  mercurial  manom- 
eter the  mercury  may  fall  in  the  arm  farthest  away  from  the  vein  and  will 
rise  in  the  arm  nearest  the  vein,  the  action  being  that  of  suction  rather  than 
pressure.  In  the  large  veins  of  the  neck  the  tendency  to  suck  in  air  is  es- 
pecially marked,  and  is  the  cause  of  death  in  some  accidents  or  operations  in 
that  region.  The  amount  of  pressure  in  the  brachial  vein  is  said  to  support 
9  mm.  of  mercury,  whereas  the  pressure  in  the  veins  of  the  neck  may  fall  to 
a  negative  pressure  of  from  —  3  to  —  8  mm. 

The  variations  of  venous  pressure  during  systole  and  diastole  of  the 
heart  are  very  slight,  and  a  distinct  pulse  is  never  seen  in  veins  except  under 
extraordinary  circumstances.  In  certain  forms  of  cardiac  valvular  insuffi- 
ciency there  may  be  considerable  regurgitation  of  the  blood  with  a  strong 
venous  pulse. 

Careful  observations  upon  the  web  of  the  frog's  foot,  the  tongue  and  mesen- 
tery of  the  frog,  the  tails  of  newts  and  small  fishes,  and  upon  the  skin  of  the 
finger  behind  the  nail  (von  Kries) ;  as  well  as  estimations  of  the  amount  of 
pressure  required  to  empty  the  vessels  of  blood  under  various  conditions, 
all  indicate  that  the  capillary  blood  pressure  is  subject  to  very  great  varia- 
tions. Apparently  the  variations  follow  the  variations  of  pressure  in  the 
arteries,  though  the  measurements  of  the  capillary  pressure  of  the  skin 
in  man  indicate  that  it  is  occasionally  markedly  influenced  by  the  venous 
pressure  variations. 

The  pulse  in  the  arterioles,  capillaries,  and  venules  becomes  more  and 
more  evident  as  the  extravascular  pressure  is  increased.  The  pressure  in 
the  web  of  the  frog's  foot  has  been  found  to  be  equal  to  about  14  to  20  mm.  of 
mercury;  in  other  capillary  regions  the  pressure  is  found  to  be  equal  to  from 
one-fifth  to  one-half  of  the  ordinary  arterial  pressure. 

General  Variations  in  Blood  Pressure.  The  arterial  blood  pressure 
may  be  made  to  vary  by  alterations  in  either  of  the  chief  factors  upon  which 
the  pressure  in  the  vessels  depends,  but  primarily  by  the  cardiac  contrac- 
tions and  the  peripheral  resistance.  Thus,  increase  of  blood  pressure  may 
be  brought  about  by  either,  1,  a  more  frequent  or  more  forcible  action  of 
the  heart,  or,  2,  by  an  increase  of  the  peripheral  resistance.  On  the  other 
hand,  diminution  of  the  blood  pressure  may  be  produced,  either  by  a,  a 
diminished  force  or  frequency  of  the  contractions  of  the  heart,  or  by  b,  a 
diminished  peripheral  resistance.     These  different  factors,  however,  although 


196 


THE     CIRCULATION    OF    THE     HLOOD 


varying  constantly,  are  so  combined  that  the  general  arterial  pressure  re- 
mains fairly  constant.  For  example,  the  heart  may,  by  increased  force  or 
frequency  of  its  contractions,  distinctly  increase  the  blood  pressure,  but  this 
increased  action  is  almost  certainly  followed  by  diminished  peripheral  re- 
sistance, and  thus  the  two  altered  conditions  may  balance,  with  the  result 
of  bringing  back  the  blood  pressure  to  what  it  was  before  the  heart  began 
to  beat  more  rapidly  or  more  forcibly. 

It  will  be  clearly  seen  that  the  circulation  of  the  blood  within  the  blood 
vessels  must  depend  upon  the  diminution  of  the  pressure  from  the  heart 
to  the  capillaries,  and  from  the  capillaries  to  the  veins,  the  blood  flowing  in 


Fig.  191. — Schema  Showing  the  Relation  between  Blood  Pressure,  Velocity  of  Flow,  and 
Vascular  Area,  in  the  Arteries,  Capillaries,  and  Veins.  Ordinates  represent  height  of  pressure  and 
speed  of  flow.  The  abscissa,  b-c,  represents  zero  pressure  and  speed.  Space  between  lines  a-b  and 
d-e  represents  arterial  system;  between  d-e  and  f-g,  capillary  system,  and  between  j-g  and  h-i,  the 
venous  system.  Line  A-B  equals  pressure;  line  C-D,  speed  of  flow;  and  line  E-F,  vascular  area. 
(Modified  from  Gad.) 


the  direction  of  least  resistance.  We  shall  presently  see  further  that  the 
local  flow  also  depends  upon  the  relations  between  the  heart's  action  and 
the  peripheral  resistance  both  general  and  local. 

The  Arterial  Flow.  The  character  of  the  flow  of  blood  through 
the  arterial  system  depends  to  a  very  considerable  extent  upon  the  structure 
of  the  arterial  walls,  and  particularly  upon  the  elastic  tissue  which  is  so  highly 
developed  in  them. 

The  elastic  tissue  of  the  arteries,  first  of  all,  guards  them  from  the  sud- 
denly exerted  pressure  to  which  they  are  subjected  at  each  contraction  of  the 
ventricles.  In  every  such  contraction,  as  is  above  seen,  the  contents  of  the 
ventricles  are  forced  into  the  arteries  more  quickly  than  they  are  discharged 
through  the  capillaries.  The  blood,  therefore,  being  for  an  instant  resisted 
in  its  onward  course,  a  part  of  the  force  with  which  it  is  impelled  is  directed 
against  the  sides  of  the  arteries;    under  this  force  their  elastic  walls  dilate, 


THE     ARTERIAL     FLOW 


197 


stretching  enough  to  receive  the  blood,  and  becoming  more  tense  and  more 
resisting  as  they  stretch.  Thus  by  yielding  they  break  the  shock  of  the 
force  impelling  the  blood.  On  the  subsidence  of  the  pressure,  should  the 
ventricles  cease  contracting,  the  arteries  are  able  by  the  same  elasticity  to 
resume  their  former  caliber. 

The  elastic  tissue  in  the  same  way  equalizes  the  current  of  blood  by  main- 
taining pressure  on  it  in  the  arteries  during  the  ueriod  at  which  the  ventri- 


Fig.  192. — Cross  Section  of  the  Aorta  to  Show  Elastic  Tissue;  e,  elastic  elements.    (Bailey.) 


cles  are  at  rest  or  are  dilating.  If  the  arteries  were  rigid  tubes,  the  blood, 
instead  of  flowing  as  it  does  in  a  constant  stream,  would  be  propelled  through 
the  arterial  system  in  a  series  of  spurts  corresponding  in  time  to  the  ventric- 
ular contractions  and  with  intervals  of  almost  complete  rest  during  the  in- 
action of  the  ventricles.  But  in  the  actual  condition  of  the  vessels,  the  force 
of  the  successive  contractions  of  the  ventricles  is  expended  partly  in  the 
direct  propulsion  of  the  blood,  and  partly  in  the  dilatation  of  the  elastic  ar- 
teries; and  in  the  intervals  between  the  contractions  of  the  ventricles,  the 
force  of  the  recoil  is  employed  in  continuing  the  flow  onward.  Of  course 
the  pressure  exercised  is  equally  diffused  in  every  direction,  and  the  blood 


1!)K  THE    CIRCULATION    OF    THE    BLOOD 

tends  to  move  backward  as  well  as  onward.  All  movement  backward, 
however,  is  prevented  by  the  closure  of  the  semilunar  valves,  which  takes 
place  at  the  very  commencement  of  the  recoil  of  the  arterial  walls. 

The  Arterial  Flow  is  Rhythmic.  By  the  exercise  of  the  elasticity 
of  the  arteries,  all  the  force  of  the  ventricles  is  expended  upon  the  circulation. 
That  part  of  the  force  which  is  used  up  or  rendered  potential  in  dilating  the 
arteries  is  restored  or  made  active  or  kinetic  when  they  recoil.  There  is  no 
loss  of  force,  neither  is  there  any  gain;  for  the  elastic  walls  of  the  artery 
cannot  originate  any  force  for  the  propulsion  of  the  blood;  they  only  restore 
that  which  they  receive  from  the  ventricles. 

Since  the  ventricular  discharge  is  intermittent,  there  will  be  intermittent 
accessions  of  pressure,  and  therefore  the  flow  of  blood  in  the  arteries  will 
be  periodically  accelerated.  The  volume  of  blood  discharged  from  a  cut 
artery  increases  and  decreases  with  the  systole  and  diastole  of  the  ventricles, 
or  with  the  systolic  and  diastolic  pressures  of  the  arteries  themselves,  see 
page  187. 

This  equalizing  influence  of  the  resistance  of  the  successive  arterial 
branches  reacts  so  that  at  length  the  intermittent  accelerations  produced 
in  the  arterial  flow  by  the  discharge  of  the  heart  cease  to  be  observable,  and 
the  jetting  stream  is  converted  into  the  continuous  and  even  movement  of 
the  blood  which  we  see  in  the  capillaries  and  veins.  In  the  production  of  a 
continuous  stream  of  blood  in  the  smaller  arteries  and  capillaries,  the  resist- 
ance which  is  offered  to  the  blood  stream  in  these  vessels  is  a  necessary  agent. 
Were  there  no  greater  obstacle  to  the  escape  of  blood  from  the  larger  arteries 
than  exists  to  its  entrance  into  them  from  the  heart,  the  stream  would  be 
intermittent,  notwithstanding  the  elasticity  of  the  walls  of  the  arteries. 

The  muscular  element  of  the  middle  coat  cooperates  with  the  elastic  in 
adapting  the  caliber  of  the  vessels  to  the  quantity  of  blood  which  they  contain; 
for  the  amount  of  fluid  in  the  blood-vessels  varies  quite  considerably  even 
from  hour  to  hour,  and  can  never  be  quite  constant;  and  were  the  elastic 
tissue  only  present,  the  pressure  exercised  by  the  walls  of  the  containing 
vessels  on  the  contained  blood  would  be  sometimes  very  small,  and  some- 
times inordinately  great.  The  presence  of  a  muscular  element,  however, 
provides  for  a  certain  uniformity  in  the  amount  of  pressure  exercised;  and 
it  is  by  this  adaptive,  uniform,  gentle  muscular  contraction  that  the  normal 
tone  of  the  blood-vessels  is  maintained.  Deficiency  of  this  tone  is  the  cause 
of  the  soft  and  yielding  arterial  pulse,  and  the  sluggish  blood  flow  through 
the  arterioles. 

Incidentally  it  may  be  mentioned  that  the  elastic  and  muscular  contrac- 
tion of  an  artery  may  also  be  regarded  as  fulfilling  a  natural  purpose  when, 
the  artery  being  cut,  the  sudden  contraction  at  first  limits,  and  then,  in  con- 
junction with  the  coagulated  fibrin,  completely  arrests,  the  flow  of  blood. 
It  is  only  in  consequence  of  such  contraction  and  coagulation  that  we  are 


THE  VELOCITY  OF  THE  ARTERIAL  BLOOD  FLOW        199 

free  from  danger  through  even  very  slight  wounds;  for  it  is  only  when  the 
artery  is  closed  that  the  processes  for  the  more  permanent  and  secure  pre- 
vention of  bleeding  are  established. 

The  Velocity  of  the  Arterial  Blood  Flow.  The  velocity  of  the 
blood  current  at  any  given  point  in  the  various  divisions  of  the  circulatory 
system  is  inversely  proportional  to  their  united  sectional  area  at  that  point. 
If  the  united  sectional  area  of  all  the  branches  of  a  vessel  were  always  the  same 
as  that  of  the  vessel  from  which  they  arise,  and  if  the  aggregate  sectional 
area  of  the  capillary  vessels  were  equal  to  that  of  the  aorta,  the  mean  rapidity 
of  the  blood's  motion  in  the  small  arteries  and  in  the  capillaries  would  be  the 
same  as  in  the  aorta.  If  a  similar  correspondence  of  capacity  existed  in  the 
veins  there  would  be  an  equal  correspondence  in  the  rapidity  of  the  circula- 
tion in  them.  But  the  arterial  and  venous  systems  may  be  represented  by 
two  truncated  cones  with  their  apices  directed  toward  the  heart;  the  area  of 
their  united  bases,  the  sectional  area  of  the  capillaries,  being  four  hundred 
to  eight  hundred  times  as  great  as  that  of  the  truncated  apex  representing 
the  aorta.  Thus  the  velocity  of  blood  in  the  smallest  arterioles  and  the 
capillaries  is  not  more  than  one -four-hundredth  of  that  in  the  aorta. 

The  velocity  of  the  stream  of  blood  is  greatest  in  the  neighborhood  of 
the  heart.  The  rate  of  movement  is  greatest  during  the  ventricular  systole 
and  diminishes  during  the  diastole.  The  rate  of  flow  also  decreases  along 
the  arterial  system,  becoming  least  in  the  parts  of  the  system  most  distant 
from  the  heart.  Chauveau  has  estimated  the  rapidity  of  the  blood  stream 
in  the  carotid  of  the  horse  at  over  20  inches  per  second  during  the  heart's 
systole,  and  nearly  6  inches  during  the  diastole  (520-150  mm.),  see  figure  191. 

The  Capillary  Flow.  It  is  in  the  capillaries  that  the  chief  resistance 
is  offered  to  the  progress  of  the  blood;  for  in  them  the  friction  of  the  blood 
is  greatly  increased  by  the  enormous  multiplication  of  the  surface  with  which 
it  is  brought  in  contact. 

When  the  capillary  circulation  is  examined  in  any  transparent  part  of  a 
full-grown  living  animal  by  means  of  the  microscope,  figures  193,  194,  the 
blood  is  seen  to  flow  with  a  constant  equable  motion;  the  red  blood-corpus- 
cles moving  along,  mostly  in  single  file,  and  bending  in  various  ways  to  ac- 
commodate themselves  to  the  tortuous  course  of  the  capillary,  but  instantly 
recovering  their  normal  outline  on  reaching  a  wider  vessel, 

At  the  circumference  of  the  stream  and  adhering  to  the  walls  of  the  larger 
capillaries,  but  especially  well  marked  in  the  small  arteries  and  veins,  there 
is  a  layer  of  plasma  which  appears  to  be  motionless.  The  existence  of  this 
still  layer,  as  it  is  termed,  is  inferred  both  from  the  general  fact  that  such  a 
one  exists  in  all  fine  tubes  traversed  by  fluid,  and  from  what  can  be  seen  in 
watching  the  movements  of  the  blood-corpuscles.  The  red  corpuscles  occupy 
the  middle  of  the  stream  and  move  with  comparative  rapidity;  the  color- 
less corpuscles  run  much  more  slowly  by  the  walls  of  the  vessels;   while  next 


200 


THE    CIRCULATION     OF    THE     BLOOD 


to  the  wall  there  is  a  transparent  space  in  which  the  fluid  appears  to  be  at 
rest;  for  if  any  of  the  corpuscles  happen  to  be  forced  within  it,  they  move 
more  slowly  than  before,  rolling  lazily  along  the  side  of  the  vessel,  and  often 
adhering  to  its  wall,  figure  194.  Part  of  this  slow  movement  of  the  colorless 
corpuscles  and  their  occasional  stoppage  may  be  due  to  their  having  a  tend- 
ency to  adhere  to  the  walls  of  the  vessels.  Sometimes,  indeed,  when  the 
motion  of  the  blood  is  not  strong,  many  of  the  white  corpuscles  collect 
in  a  capillary  vessel,  and  for  a  time  entirely  prevent  the  passage  of  the  red 
corpuscles. 

When  the  peripheral  resistance  is  greatly  diminished  by  the  dilatation  of 
the  small  arteries  and  capillaries,  so  much  blood  passes  on  from  the  arteries 
into  the  capillaries  at  each  stroke  of  the  heart  that  there  is  not  sufficient 
remaining  in  the  arteries  to  distend  them.  Thus,  the  intermittent  current 
of  the  ventricular  systole  is  not  always  converted  into  a  continuous  stream 
by  the  elasticity  of  the  arteries  before  the  capillaries  are  reached;  and  so 
intermittency  of  the  (low  occurs  both  in  capillaries  and  veins  and  a  venous 
pulse  is  produced.     The  same  phenomenon  may  occur  when  the  arteries 


Fig.  193. — Capillary  Network  from  Human  Pia  Mater,  Showing  also  an  Arteriole  in  "  Optical 
Section  ";  and  a  Small  Vein.  X  350.  A,  Vein;  B,  arteriole;  C,  large  capillary;  D,  small  capillaries. 
(Bailey.) 


become  rigid  from  disease,  and  when  the  beat  of  the  heart  is  so  slow  or  so 
feeble  that  the  blood  at  each  cardiac  systole  has  time  to  pass  on  to  the  capil- 
laries before  the  next  stroke  occurs;  the  amount  of  blood  sent  at  each  stroke 
being  insufficient  properly  to  distend  the  elastic  arteries. 

It  was  formerly  supposed  that  the  occurrence  of  any  transudation  from 
the  interior  of  the  capillaries  into  the  midst  of  the  surrounding  tissues  was 
confined,  in  the  absence  of  injury,  strictly  to  the  fluid  part  of  the  blood;   in 


THE     CAPILLARY     FLOW 


^01 


other  words,  that  the  corpuscles  could  not  escape  from  the  circulating  stream, 
unless  the  wall  of  the  containing  blood-vessel  was  ruptured.     It  is  true  that 
the  English  physiologist  Augustus  Waller  affirmed  in  1846  that  he  had  seen 
blood-corpuscles,    both   red   and   white,   pass  bodily 
through   the   wall   of    the  capillary  vessel    in  which 
they    were    contained    (thus    confirming   what    had 
been   stated   a   short   time   previously   by  Addison), 
and  that  as  no  opening  could  be  seen  before  their 
escape,    so   none   could    be    observed  afterward,    so 
rapidly  was  the  part  healed.     But  these  observations 
did  not  attract   much   notice    until  the  phenomenon 
of   escape  of   the    blood-corpuscles  from    the   capil- 
laries and  minute  veins,  apart  from  mechanical  injury, 
was  rediscovered  by  Cohnheim  in  1867. 

Cohnheim's  experiment  demonstrating  the  pas- 
sage of  the  corpuscles  through  the  wall  of  the  blood- 
vessel is  performed  in  the  following  manner:  A  frog 
is  curarized,  that  is  to  say  paralysis  is  produced  by 
injecting  under  the  skin  a  minute  quantity  of  the 
poison  called  curari.  The  abdomen  is  then  opened, 
a  portion  of  the  small  intestine  is  drawn  out,  and  its 
transparent  mesentery  spread  out  under  a  microscope. 
After  a  variable  time,  occupied  by  dilatation  following 
contraction  of  the  minute  vessels  and  the  accom- 
panying quickening  of  the  blood  stream,  there  ensues  a  retardation  of  the 
current  and  the  red  and  white  blood-corpuscles  begin  to  make  their  way 
through  the  capillaries  and  small  veins. 

The  white  corpuscles  pass  through  the  capillary  wall  chiefly  by  the  ame- 
boid movement  with  which  they  are  endowed.  This  migration  occurs  to  a 
limited  extent  in  health,  but  in  inflammatory  conditions  is  much  increased. 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs  under  cir- 
cumstances of  impeded  venous  circulation,  and  consequently  increased 
blood  pressure,  resembles  closely  the  migration  of  the  leucocytes,  with  the 
exception  that  they  are  squeezed  through  the  wall  of  the  vessel,  and  do  not, 
like  the  leucocytes,  work  their  way  through  by  ameboid  movement. 

Various  explanations  of  these  remarkable  phenomena  have  been  sug- 
gested. Some  believe  that  pseudo-stomata  between  contiguous  endothelial 
cells  provide  the  means  of  escape  for  the  blood-corpuscles.  But  the  chief 
share  in  the  process  is  probably  due  to  mobility  and  contraction  of  the  parts 
concerned,  both  of  the  corpuscles  and  of  the  capillary  wall  itself. 

The  Speed  of  the  Blood  in  the  Capillaries.  The  velocity  of  the 
blood  through  the  capillaries  must,  of  necessity,  be  largely  influenced  by 
that  which  occurs  in  the  vessels  on  both  sides  of  them,  in  the  arteries  and 


Fig.  194. — A  Large  Cap- 
illary from  the  Frog's 
Mesentery  Eight  Hours 
after  Irritation  had  been 
set  up,  Showing  Emigra- 
tion of  Leucocytes.  a. 
Cells  in  the  act  of  travers- 
ing the  capillary  wall;  b, 
some  already  escaped. 
(Frey.) 


202  THE     CIRCULATION     OF    THE     BLOOD 

the  veins,  their  intermediate  position  causing  them  to  respond  at  once  to  any 
alteration  in  the  size  or  rate  of  the  arterial  or  venous  blood  stream.  Thus,  the 
apparent  contraction  of  the  capillaries,  on  the  application  of  certain  irritating 
substances  or  during  certain  mental  states,  and  their  dilatation  in  blushing 
may  be  referred  primarily  to  the  corresponding  action  of  the  small  arteries. 

The  Measurement  0}  Velocity  in  the  Capillaries.  The  observation  of 
Hales,  E.  H.  Weber,  and  Valentin  agree  very  closely  as  to  the  rate  of  the 
blood  current  in  the  capillaries  of  the  frog;  and  the  mean  of  their  estimates 
gives  the  velocity  of  the  systemic  capillary  circulation  at  about  0.5  mm.  per 
second.  The  velocity  in  the  capillaries  of  warm-blooded  animals  is  greater, 
in  the  dog  0.5  to  0.75  mm.  per  second.  This  may  seem  inconsistent  with  the 
facts,  which  show  that  the  whole  circulation  is  accomplished  in  about  half 
a  minute.  But  the  whole  length  of  capillary  vessels,  through  which  any 
given  portion  of  blood  has  to  pass,  probably  does  not  exceed  0.5  mm.  There- 
fore the  time  required  for  each  quantity  of  blood  to  traverse  its  own  appointed 
portion  of  the  general  capillary  system  will  scarcely  amount  to  more  than  a 
second.  This  comparatively  slow  velocity  is  evidently  favorable  to  the 
nutritive  interchanges  that  go  on  through  these  thin-walled  vessels  between 
the  blood  within  the  capillaries  and  the  outside  active  tissues. 

The  Venous  Flow.  The  blood  current  in  the  veins  is  maintained, 
a,  primarily  by  the  contractions  of  the  left  ventricle;  but  very  effectual  assist- 
ance to  the  flow  is  afforded,  b,  by  the  action  of  the  muscles  capable  of  pressing 
on  the  veins  with  valves,  and  c,  by  the  aspiration  of  the  thorax  and  possibly, 
d,  by  the  aspiration  of  the  heart  itself. 

The  effect  of  muscular  pressure  upon  the  circulation  may  be  thus  ex- 
plained: When  pressure  is  applied  to  any  part  of  a  vein,  and  the  current  of 
blood  in  it  is  obstructed,  the  portion  behind  the  seat  of  pressure  becomes 
swollen  and  distended  as  far  back  as  the  next  pair  of  valves,  which  are  in 
consequence  closed.  Thus,  whatever  force  is  exercised  by  the  external 
pressure  of  the  muscles  on  the  veins,  is  distributed  partly  in  pressing  the  blood 
onward  in  the  proper  course  of  the  circulation,  and  partly  in  pressing  it 
backward  and  closing  the  valves  behind. 

The  circulation  might  lose  as  much  as  it  gains  by  such  an  action,  if  it 
were  not  for  the  numerous  communications,  or  venous  anastomoses;  for  owing 
to  these  anastomoses  the  closing  up  of  the  venous  channel  by  the  backward 
pressure  is  prevented  from  being  any  serious  hindrance  to  the  circulation, 
since  the  blood  which  is  arrested  in  its  onward  course  by  the  closed  valves 
can  at  once  pass  through  some  anastomosing  channel,  and  proceed  on  its 
way  by  another  vein.  Thus  the  effect  of  muscular  pressure  upon  veins 
which  have  valves  is  turned  almost  entirely  to  the  advantage  of  the  circula- 
tion; the  pressure  of  the  blood  onward  is  all  advantageous,  and  the  pressure 
of  the  blood  backward  is  prevented  from  being  a  hindrance  by  the  closure 
of  the  valves  and  of  the  anastomoses  of  the  veins. 


THE     VELOCITY     IN     THE     VEINS  203 

The  venous  flow  is  also  assisted  by  the  aspiration  of  the  thorax  and  to 
some  extent  by  that  of  the  heart,  since  at  some  time  during  every  cardiac 
cycle  the  intraauricular  and  intraventricular  pressure  falls  below  that  of 
the  atmosphere.  This  activity  will  be  considered  more  fully  in  the  chapter 
on  Respiration.  In  this  connection  it  may  be  said,  however,  that  the  pressure 
in  the  great  veins  falls  during  inspiration  and  rises  during  expiration. 

The  Velocity  in  the  Veins.  The  velocity  of  the  blood  is  greater 
in  the  veins  than  in  the  capillaries,  but  less  than  in  the  arteries;  this  fact 
depending  upon  the  relative  capacities  of  the  arterial  and  venous  systems. 
If  an  accurate  estimate  of  the  proportionate  areas  of  arteries  and  the  veins 
corresponding  to  them  could  be  made,  we  might,  from  the  velocity  of  the 
arterial  current,  calculate  that  of  the  venous.  The  usual  estimate  is  that 
the  capacity  of  the  veins  is  about  two  or  three  times  as  great  as  that  of  the 
arteries,  and  that  the  velocity  of  the  blood's  motion  is,  therefore,  about  one-half 
or  one-third  as  great  in  the  veins  as  in  the  arteries,  i.e.,  200  mm.  a  second. 
The  rate  at  which  the  blood  moves  in  the  smallest  venules  is  only  slightly 
greater  than  that  in  the  capillaries,  but  the  speed  of  flow  gradually  increases 
the  nearer  the  vessel  approaches  to  the  heart,  for  the  sectional  area  of  the 
venous  trunks,  compared  with  that  of  the  branches  opening  into  them,  be- 
comes gradually  smaller  as  the  trunks  advance  toward  the  heart,  figure  191. 

The  Velocity  of  the  Circulation  as  a  Whole.  It  would  appear 
that  a  portion  of  blood  can  traverse  the  entire  course  of  the  circulation,  in 
the  horse,  in  half  a  minute.  Of  course  it  would  require  longer  to  traverse 
the  vessels  of  the  most  distant  part  of  the  extremities  than  to  go  through 
those  of  the  neck,  but  taking  an  average  length  of  the  vessels  to  be  traversed 
it  may  be  concluded  that  half  a  minute  represents  the  average  rate.  Stewart 
estimated  that  the  circulation  time  in  man  is  probably  not  less  than  twelve 
nor  more  than  fifteen  seconds. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results  of  experi- 
ments to  ascertain  the  rapidity  with  which  chemicals  introduced  into  the  blood 
are  transmitted  from  one  part  of  the  vascular  system  to  another.  The  time 
required  for  the  passage  of  solutions  of  potassium  ferrocyanide,  mixed  with 
the  blood,  from  one  jugular  vein,  through  the  right  side  of  the  heart,  the 
pulmonary  vessels,  the  left  cavities  of  the  heart,  and  the  general  circulation, 
to  the  jugular  vein  of  the  opposite  side,  varies  from  twenty  to  thirty  seconds 
in  the  dog.  The  same  substance  is  transmitted  from  the  jugular  vein  to  the 
great  saphenous  vein  in  twenty  seconds;  from  the  jugular  vein  to  the  mes- 
enteric artery  in  between  fifteen  and  thirty  seconds;  to  the  facial  artery, 
in  one  experiment,  in  between  ten  and  fifteen  seconds;  in  another  experi- 
ment, in  between  twenty  and  twenty-five  seconds;  in  its  transit  from  the 
jugular  vein  to  the  metatarsal  artery,  it  occupies  between  twenty  and  thirty 
seconds.  The  result  is  said  to  be  nearly  the  same  whatever  the  rate  of  the 
heart's  action.     In  more  recent  methods  some  innocuous  dye  like  methylene 


2()4  THE    CIRCULATION    OF    THE     BLOOD 

blue  is  used,  since  it  permits  the  determination  without  the  loss  of  blood, 
the  change  in  color  being  visible  through  the  walls  of  the  blood-vessels. 

Stewart  has  made  most  accurate  measurements  of  the  circulation  time 
by  the  electrical-resistance  method.  Strong  salt  solutions  injected  into  the 
jugular  vein  on  one  side  when  they  reach  the  other  jugular  (or  any  other 
vessel)  are  instantly  detected  by  a  decrease  in  the  electrical  resistance  through 
the  vessel  when  it  is  laid  between  the  poles  of  the  proper  conductivity 
apparatus. 

In  all  these  experiments  it  is  assumed  that  the  substance  injected  moves 
with  the  blood  and  at  the  same  rate,  and  does  not  move  from  one  part  of 
the  organs  of  circulation  to  another  by  diffusing  itself  through  the  blood  or 
tissues  more  quickly  than  the  blood  moves.  The  assumption  may  be  ac- 
cepted that  the  times  above  mentioned  as  occupied  in  the  passage  of  the  in- 
jected substances  are  the  times  in  which  the  portion  of  blood  itself  is  carried 
from  one  part  to  another  of  the  vascular  system. 

Another  mode  of  estimating  the  general  velocity  of  the  circulating  blood 
is  by  calculating  it  from  the  quantity  of  blood  supposed  to  be  contained  in 
the  body,  and  from  the  quantity  which  can  pass  through  the  heart  in  each 
of  its  contractions.  But  the  conclusions  arrived  at  by  this  method  are  less 
satisfactory.  For  the  total  quantity  of  blood,  and  the  capacity  of  the  cavities 
of  the  heart,  have  as  yet  been  only  approximately  ascertained.  Still  the  most 
careful  of  the  estimates  thus  made  accord  very  nearly  with  those  already 
mentioned;  and  it  may  be  assumed  that  the  blood  may  all  pass  through 
the  heart  in  about  twenty-five  seconds. 

THE    PULSE. 

The  most  characteristic  feature  of  the  arterial  pressure  and  blood  flow 
is  its  intermittency,  and  this  intermittent  flow  is  seen  or  felt  as  waves  of  change 
in  diameter  of  the  arteries,  known  as  the  Pulse. 

The  pulse  is  generally  described  as  a  wave-like  expansion  of  the  artery 
produced  by  the  injection  of  blood  at  each  ventricular  systole  into  the  already 
full  aorta.  The  force  of  the  left  ventricle  is  expended  in  pressing  the  blood 
forward  and  in  dilating  the  aorta.  With  the  injection  of  each  new  quantity 
of  blood  into  the  aorta  there  is  a  wave  of  dilatation  which  passes  on,  expanding 
the  arteries  as  it  goes,  running  as  it  were  over  the  more  slowly  traveling  blood 
contained  in  them,  and  producing  the  pulse  as  it  proceeds.  A  sharp  dis- 
tinction must  be  made  between  the  passage  of  the  pulse  wave  along  an  artery 
and  the  rate  of  flow  of  the  blood  in  the  vessel.  The  pulse  produced  by  any 
given  beat  of  the  heart  is  not  felt  at  the  same  moment  in  all  parts  of  the  body. 
Thus,  it  can  be  felt  in  the  carotid  a  short  time  before  it  is  perceptible  in  the 
radial  arterv,  and  in  this  vessel  before  it  occurs  in  the  dorsal  artery  of  the 
foot.     Careful  measurements  of  the  intervals  between  the  time  of  the  pulse 


THK    SPHYGMOGRAPH 


205 


at  the  carotid  and  at  the  wrist  shows  that  the  delay  in  the  beat  is  in  proportion 
to  the  distance  of  the  artery  from  the  heart.  The  difference  in  time  between 
the  pulse  of  any  two  arteries  probably  never  exceeds  one-sixth  to  one-eighth 
of  a  second.  The  rate  at  which  the  pulse  travels  in  the  arteries  is  from  five  to 
ten  meters  per  second. 

The  distention  of  each  artery  increases  both  its  length  and  its  diameter. 
In  their  elongation  the  arteries  change  their  form,  the  straight  ones  becoming 
slightly  curved,  and  those  already  curved  becoming  more  so;  but  they  re- 
cover their  previous  form  as  well  as  their  diameter  when  the  ventricular 
contraction  ceases,  and  their  elastic  walls  recoil.  The  increase  of  their 
curves  which  accompanies  the  distention  of  arteries,  and  the  succeeding 
recoil,  may  be  well  seen  in  the  prominent  temporal  artery  of  an  old  person. 
In  feeling  the  pulse,  the  finger  cannot  distinguish  the  sensation  produced 
by  the  dilatation  from  that  produced  by  the  elongation  and  curving.  That 
which  it  perceives  most  plainly,  however,  is  the  dilatation  and  return  more 
or  less  to  the  cylindrical  form  of  the  artery,  which  has  been  partially  flattened 
by  the  finger. 

The  Sphygmograph.  Much  light  has  been  thrown  on  what  may 
be  called  the  form  of  the  pulse  wave  by  an  instrument  called  the  sphygmo- 


Fig.  195. — Diagram  of  the  Lever  of  the  Sphygmograph. 


graph,  figures  195  and  196.  The  principle  on  which  it  acts  will  be  seen 
on  reference  to  the  figures. 

A  small  button  replaces  the  finger  in  the  act  of  taking  the  pulse.  This 
button  is  made  to  rest  lightly  on  the  artery  the  pulsations  of  which  it  is  de- 
sired to  investigate.  The  up-and-down  movement  of  the  button  is  com- 
municated to  the  lever,  to  the  hinder  end  of  which  is  attached  a  light  spring. 
The  spring  is  adjusted  to  the  proper  tension  to  follow  the  movements  of  the 
artery  wall  during  the  pulse  wave.  The  sphygmograph  is  bound  on  the 
wrist  while  taking  a  record. 

It  is  evident  that  the  beating  of  the  pulse  will  cause  an  up-and-down 
movement  of  the  lever,  the  pen  of  which  will  write  the  effect  on  a  smoked 
card  moved  by  the  clock-work  of  the  instrument. 


£06 


THE     CIRCULATION     OF    THE     BLOOD 


Thus  a  tracing  of  the  pulse  is  obtained,  and  in  this  way  much  more  deli- 
cate changes  can  be  seen  than  can  be  felt  by  the  mere  application  of  the  finger. 

The  principle  of  the  sphygmometer  of  Roy  and  Adami  is  shown  in  the  diagram,  figure 
197. 

The  apparatus  consists  of  a  box,  a,  which  is  moulded  to  fit  over  the  end  of  the  radius 
so  as  to  DriQge  over  the  radial  artery.  Within  this  is  a  flexible  bag,  b,  filled  with  water, 
and  connected  by  a  T-tube  with  a  rubber  bag,  h,  and  mercurial  manometer.  The  fluid 
in  the  box  may  be  raised  to  any  desired  pressure,  and  may  then  be  shut  off  by  tap,  c-  At 
the  upper  part  of  the  box  is  a  circular  opening,  and  resting  upon  b  is  a  flat  button,  d, 
which  by  means  of  a  short  light  rod,  e,  communicates  the  movement  of  b  to  the  lever,  /. 
At  the  axis  of  rotation  of  this  lever  is  a  spiral  watch-spring,  g,  which  can  be  tightened  at 
will,  so  that  the  lever  can  be  made  to  take  a  vertical  position  at  any  desired  hydrostatic 


Fig.  196. — Dudgeon's  Sphygmograph. 

pressure  within  the  box.  The  movements  of  the  lever  are  recorded  upon  a  piece  of  black- 
ened glazed  paper  made  to  move  in  a  vertical  direction  past  it.  When  in  use,  the  box 
is  fixed  upon  the  wrist  by  an  appropriate  holder,  and  the  pressure  is  raised  to  any  desired 
height  to  which  the  lever  is  adapted  by  tightening  or  slackening  the  spring;  the  tap,  c,  is 
then  closed.  The  pressure  within  the  box  acts  in  all  directions,  and  is  correctly  indicated 
by  the  manometer. 

Sphygmogram.  The  tracing  of  the  pulse  obtained  by  the  use  of 
the  sphygmograph,  called  a  sphygmogram,  differs  somewhat  according  to 
the  artery  from  which  it  is  taken,  but  its  general  characters  are  much  the 
same  in  all  cases.  It  consists  of  a  sudden  upstroke,  or  anacrotic  limb,  figure 
198,^,  which  is  somewhat  higher  and  more  abrupt  in  the  pulse  of  the  carotid 
and  of  other  arteries  near  the  heart  than  in  the  radial  and  other  arteries 
more  remote;  and  a  gradual  decline  or  catacrotic  limb,  B,  less  abrupt,  and 
taking  a  longer  time  than  A.  It  is  seldom,  however,  that  the  decline  is  an 
uninterrupted  fall;    it  is  usually  marked  about  half-way  by  a  distinct  notch, 


SPHYGMOGRAM 


207 


C,  called  the  dicrotic  notch,  followed  immediately  by  a  second  more  or  less 
marked  ascent  of  the  lever  called  the  dicrotic  wave,  D.  Not  infrequently 
there  is  also  at  the  beginning  of  the  descent  a  slight  wave  previous  to  the 
dicrotic  notch;  this  is  called  the  pre-dicrotic  wave,  and  in  addition  there 
may  be  one  or  more  slight  waves  after  the  dicrotic,  called  post-dicrotic,  E. 
The  interruptions  in  the  downstroke  are  called  the  catacrotic  waves  to  dis- 
tinguish them  from  an  interruption  in  the  upstroke,  called  the  anacrotic 
wave,  which  is  sometimes  met  with. 

The  explanation  of   these  tracings  presents  some  difficulties,  not,  how- 
ever, as  regards  the  two  primary  factors,  viz.,  the  upstroke  and  downstroke, 


To  manometer. 


Fig.  197. — Diagrammatic  Sectional  Representation  of  the  Sphygmometer,  a.  Box  by  which 
the  portion  of  the  artery  is  covered;  b,  thin- walled  india-rubber  bag  rilled  with  water,  and  com- 
municating through  tap,  c,  with  the  manometer  and  thick- walled  rubber  bag,  h  ;  d,  piston  con- 
nected by  rod,  e,  with  recording  lever,  f;  g,  spiral  spring,  attached  to  axis  of  lever,  and  by  which 
the  pressure  in  b,  against  the  piston,  d,  is  counterbalanced;  k,  skin  and  subcutaneous  tissue;  m, 
end  of  radius  seen  in  section;    n,  radial  artery  seen  in  section.      (Roy  and  Adami.) 

because  they  are  universally  taken  to  mean  the  sudden  injection  of  blood 
into  the  already  distended  arteries,  and  the  gradual  recovery  of  the  arteries 
by  their  recoil.  These  points  may  be  demonstrated  on  a  system  of  elastic 
tubes,  with  a  pump  to  inject  water  at  regular  intervals,  just  as  well  as  on  the 
radial  artery,  or  on  the  arterial  schema,  a  more  complicated  system  of  tubes 
in  which  the  heart,  the  arteries,  the  capillaries  and  veins  are  represented. 
If  we  place  two  or  more  sphygmographs  upon  such  a  system  of  tubes  at  in- 
creasing distances  from  the  pump,  we  may  demonstrate,  first,  that  the  rise 
of  the  lever  commences  earliest  in  that  nearest  the  pump,  and,  second,  that 
it  is  higher  and  more  sudden.  So  in  the  arteries  of  the  body  the  wave  gradu- 
ally gets  less  and  less  as  we  approach  the  periphery  of  the  arterial  system, 
and  is  lost  in  the  capillaries. 


208  THE     CIRCULATION     OF    THE     BLOOD 

The  origin  of  the  secondary  waves  is  to  some  extent  a  matter  of  uncer- 
tainty. The  anacrotic  wave  occurs  when  the  peripheral  resistance  is  high; 
that  is,  when,  for  some  time  during  the  systole,  the  flow  from  the  aorta  toward 
the  periphery  is  slower  than  the  flow  from  the  ventricle  into  the  aorta.  Thus 
it  is  seen  in  some  cases  of  nephritis  where  the  arteries  ase  rigid  and  the  periph- 
eral resistance  is  high. 

The  dicrotic  wave  is  the  most  important  of  the  secondary  waves,  and 
has  been  the  subject  of  much  discussion.     It  is  constantly  present  in  pulse- 


Fig.  198. — Diagram  of  Pulse  Tracing.     A,  upstroke  or  anacrotic  limb;  B,  downstroke  or  kat- 
acrotic  limb;   C,  pre-dicrotic  wave;   D,  dicrotic;  E,  post-dicrotic  wave. 

tracings,  but  varies  in  height.  In  point  of  time  the  dicrotic  wave  occurs 
immediately  after  the  closure  of  the  aortic  semilunar  valves.  In  certain 
conditions,  generally  of  disease,  it  becomes  so  marked  as  to  be  quite  plain 
to  the  unaided  finger.  Such  a  pulse  is  called  dicrotic.  The  generally  ac- 
cepted view  of  the  cause  of  the  dicrotic  wave  is  that  it  represents  a  rebound 
from  the  closed  aortic  valves.  During  systole,  as  the  blood  is  forcibly  in- 
jected into  the  aorta,  there  is  an  overdistention  of  the  artery.  The  systole 
suddenly  ends,  the  aorta  by  reason  of  its  elasticity  tends  to  recover  itself, 


Fig.  199. — Sphygmogram   from    the   Radial   Artery  Taken    with   Marey's    Sphygmograpli. 

(Langendorff.) 

the  blood  is  driven  back  against  the  semilunar  valves,  closing  them  and  at 
the  same  time  giving  rise  to  a  wave,  the  dicrotic  wave,  which  begins  at  the 
heart  and  travels  onward  toward  the  periphery  like  the  primary  wave.  Ac- 
cording to  Foster,  the  conditions  favoring  the  development  of  dicrotism  are: 
1,  a  highly  extensible  and  elastic  arterial  wall;  2,  a  comparatively  low  mean 
blood  pressure,  leaving  the  extensible  reaction  free  scope  to  act;  3,  a  vigorous 
and  rapid  stroke  of  the  ventricle  discharging  into  the  aorta  a  considerable 


PERIPHERAL    REGULATION    OF    THE    FLOW    OF    BLOOD 


209 


quantity  of  blood.  The  other  secondary  waves  are  probably  due  to  the  os- 
cillations in  the  elastic  recoil  of  the  arteries,  though  some  of  them  at  least 
may  be  due  to  the  inertia  of  the  instruments  used. 

In  the  use  of  the  sphygmograph  care  must  be  taken  in  the  regulation  of 
the  pressure  of  the  spring.     If  the  pressure  be  too  great,  the  characters  of 


B 


Fig.  200. — .4,  Normal  Pulse-Tracing  from  Radial  of  Healthy  Adult  Obtained  by  the  Sphyg- 
mometer; B,  from  same  artery,  with  the  same  extra- arterial  pressure,  taken  during  acute  nasal 
catarrh. 

the  pulse  may  be  almost  entirely  obscured,  or  the  artery  may  be  completely 
obstructed  and  no  tracing  is  obtained.  On  the  other  hand,  if  the  pressure  is 
too  slight,  a  very  small  part  of  the  characters  may  be  represented  on  the  tracing. 


THE    PERIPHERAL   REGULATION   OF   THE   FLOW  OF  BLOOD. 


The  flow  of  blood  through  the  circulatory  system  depends  on  the  inter- 
action of  several  factors  which  have  already  been  mentioned  in  another  con- 
nection: The  rate  and  volume  of  the  heart-beat,  the  elasticity  of  the  blood- 
vessels, the  resistance  of  the  microscopic  peripheral  vessels,  and  the  volume 
of  blood  in  the  body.  We  have  already  learned,  page  179,  that  both  the 
rate  and  the  volume  of  the  contractions  of  the  heart  are  under  very  minute 
and  intimate  regulation  and  control  through  the  cardiac  nervous  mechanism. 
Also  we  have  found  that  there  is  intimate  coordination  between  the  activity 
of  the  circulatory  and  the  activity  of  all  other  parts  of  the  body,  a  coordina- 
tion accomplished  through  the  nervous  system.  All  regulation  which  affects 
14 


210  THE    CIRCULATION     OF    THE     BLOOD 

the  heart  must  of  necessity  affect  the  general  blood  pressure  and,  therefore, 
not  directly  any  particular  part. 

The  general  elasticity  of  the  blood-vessels,  and  of  the  arteries  in  par- 
ticular, which  makes  the  general  arterial  pressure  possible,  is  dependent 
primarily  on  the  presence  of  a  large  amount  of  elastic  connective  tissue  in 
the  walls  of  the  vessels.  The  elasticity  of  this  tissue  is  a  purely  passive 
property  which  can  be  utilized  only  by  some  positive  source  of  energy,  in 
this  instance  the  heart. 

The  Variations  in  Peripheral  Resistance.  Certain  arteries  and 
veins,  especially  the  smallest  ones,  the  arterioles,  are  supplied  with  muscular 
tissue  in  their  walls.  The  activity  of  these  muscles  in  the  vascular  com- 
plex makes  the  peripheral  regulation  of  the  flow  of  blood  possible.  They 
supply  a  tissue  which  not  only  exhibits  a  passive  elasticity  comparable  to  that 
of  the  yellow  elastic  connective  tissue,  but  upon  the  proper  stimulation  they 
actively  contract  or  relax,  thus  securing  to  the  peripheral  resistance  an  active 
adjustment  to  the  ever-varying  dynamic  conditions  of  the  vascular  apparatus. 

The  muscular  tissue  in  the  walls  of  the  vessels  increases  relatively  in 
amount  as  the  arteries  become  smaller,  so  that  in  the  arterioles  it  is  developed 
out  of  all  proportion  to  the  other  elements.  In  fact,  in  passing  from  the 
arterioles  to  the  capillary  vessels,  made  up  as  we  have  seen  of  endothelial 
cells  with  a  supporting  ground  substance  only,  the  last  change  on  the  side 
of  the  arteries,  which  occurs  as  the  vessels  become  smaller,  is  the  disappear- 
ance of  muscular  fibers. 

The  office  of  the  muscular  coat  is  to  adjust  the  size  of  the  arterioles  and, 
therefore,  the  flow  of  the  blood,  to  regulate  the  quantity  of  blood  to  be  received 
by  each  part  or  organ,  and  to  adjust  the  quantity  to  the  requirements  of  each, 
according  to  various  circumstances,  but  chiefly  according  to  the  degree  of 
activity  which  each  organ  at  different  times  exhibits.  The  amount  of  work 
done  by  each  organ  of  the  body  constantly  varies,  and  the  variations  often 
quickly  succeed  each  other,  so  that,  as  in  the  muscles  for  example,  within 
the  same  hour  a  part  may  be  now  very  active  and  now  quite  inactive.  In 
all  its  active  exercise  of  function,  such  an  organ  requires  a  larger  supply  of 
blood  than  is  sufficient  for  it  during  the  times  when  it  is  comparatively 
inactive. 

It  is  evident  that  the  heart  cannot  regulate  the  blood  supply  to  each  part 
of  the  body  at  different  periods  independently  of  the  other  parts.  Neither 
could  this  be  regulated  by  any  general  and  uniform  contraction  of  the  arteries. 
But  it  may  be  regulated  by  the  power  which  the  arteries  of  each  part  have, 
through  their  muscular  tissue,  of  contracting  or  relaxing  so  as  to  diminish 
or  increase  the  supply  of  blood,  according  to  the  requirements  of  the  par- 
ticular part  of  the  body  to  which  the  vessels  are  distributed.  Thus,  while 
the  ventricles  of  the  heart  determine  the  total  quantity  of  blood  to  be  sent 
onward  at  each  contraction,  and  the  force  of  its  propulsion,  and  while  the 


DISCOVERY     OF    THE    VASO-MOTOR     NERVES 


211 


large  and  merely  elastic  arteries  distribute  the  blood  and  equalize  its  stream, 
the  smaller  arteries  by  means  of  their  muscular  tissue  regulate  and  deter- 
mine the  proportion  of  the  whole  quantity  of  blood  which  shall  be  distributed 
to  each  particular  organ. 

The  variation  of  the  size  of  arterioles  and,  therefore,  of  the  resistance 
to  the  flow  of  the  blood  in  them  is  secured  by  the  muscular  tissue,  but  the 
muscles  are  regulated  in  their  contraction  by  the  nervous  system.  The 
muscular  tissue  in  the  blood-vessels  of  the  different  organs  of  the  body  is  also 
coordinated  by  the  same  regulative  and  controlling  influence  of  the  nervous 
system. 

The  Discovery  of  the  Vaso-motor  Nerves.  More  than  half  a 
century  ago  it  was  shown  by  Claude  Bernard  that  if  the  cervical  sympathetic 
nerve  is  divided,  the  blood-vessels  of  the  corresponding  side  of  the  head  and 


Fig.  20  i. — Small  Artery  and  Vein  of  the  Frog's  Web.  .4,  Under  normal  conditions;  B,  upon 
stimulation  of  the  sciatic  nerve;  A-,  artery;  V,  vein.  In  this  experiment  the  vein  also  showed 
well-marked  vaso-constriction.      (New  figure  by  Greene.) 


neck  become  dilated.  This  effect  is  best  seen  in  the  ear,  which  if  held  up  to 
the  light  is  seen  to  beccme  redder,  and  the  arteries  to  become  larger.  The 
whole  ear  is  distinctly  warmer  than  the  opposite  one.  This  effect  is  pro- 
duced by  removing  the  arteries  from  the  influence  of  the  central  nervous  sys- 
tem, which  influence  normally  passes  along  the  course  of  the  divided  nerve. 

If  the  peripheral  end  of  the  divided  nerve  be  stimulated  in  its  course 
toward  the  organ,  i.e.,  that  farthest  from  the  brain,  the  arteries  which  were 
before  dilated  return  to  their  natural  size,  and  the  parts  regain  their  former 
condition.     And,  besides,  if  the  stimulus  is  very  strong  or  very  long  continued, 


212 


THE    CIRCULATION     OF    THE     BLOOD 


the  amount  of  normal  constriction  is  passed  and  the  vessels  become  much 
more  contracted  than  before.  The  natural  condition,  which  is  midway 
between  extreme  contraction  and  extreme  dilatation,  is  called  the  natural 
tone  of  an  artery.     If  this  is  not  maintained,  the  vessel  is  said  to  have  lost 


Fig.  202. — Arm  Plethysmograph.  Apparatus  for  measuring  the  change  in  volume  in  the 
arm  due  to  variation  in  the  blood  supply.  The  arm  is  enclosed  in  a  glass  cylinder  which  is  com- 
pletely filled  with  fluid,  the  opening  through  which  the  arm  is  inserted  being  closed  by  a  rubber 
sleeve ,  A .  The  cavity  of  the  glass  cylinder  communicates  through  the  tube,  F,  G,  with  the  test  tube 
M,  which  is  supported  in  the  jar,  P.  Any  variation  in  volume  in  the  arm  will  cause  water  to  flow 
out  or  into  the  test  tube,  M,  which  is  lowered  as  the  tube  fills,  and  raised  as  it  empties.  The  rise 
and  fall  of  the  test  tube,  M,  is  communicated  over  the  pulley,  L,  to  the  writing-pen,  N,  which  re- 
cords the  movements  on  the  smoked  cylinder.     Kymograph  not  shown.      (Mosso.) 


tone,  or,  if  it  is  exaggerated,  the  tone  is  said  to  be  too  great.  The  effects 
described  as  having  been  produced  by  section  of  the  cervical  sympathetic 
and  by  subsequent  stimulation  are  not  peculiar  to  that  nerve  and  the  vessels 
to  which  it  is  distributed. 

It  has  been  found  that  for  every  part  of  the  body,  except  the  brain,  there 
exists  a  nerve  the  division  of  which  produces  the  same  effects,  viz.,  dilatation 
of  the  vessels.  Such  may  be  cited  as  the  case  with  the  sciatic,  the  splanch- 
nic nerves,  and  the  nerves  of  the  brachial  plexus;  when  these  are  divided, 
dilatation  of  the  blood-vessels  in  the  parts  supplied  by  them  takes  place. 
It  appears,  therefore,  that  nerves  exist  which  have  a  distinct  control  over  the 
vascular  supply  of  every  part  of  the  body.  These  are  called  vaso-motor  or 
vaso-constrictor  nerves.     But  the  arterioles  are  also  under  the  influence  of 


VASOCONSTRICTOR    NERVES  213 

a  second  set  of  nerves,  also  discovered  by  Claude  Bernard,  which  produce 
exactly  the  opposite  influence,  i.e.,  dilatation.  These  nerves  are  called  vaso- 
dilator nerves. 

Mall  has  also  shown  that  veins,  at  least  the  portal  vein,  possess  a  vaso- 
motor nerve  supply  as  well  as  arteries. 

Vaso- constrictor  Nerves.  The  presence  of  vaso-constrictor  nerves 
can  be  shown  in  several  different  ways,  of  which  the  most  convincing  is  that 
of  direct  inspection.  If  a  vascular  membrane,  like  the  web  of  the  frog's 
foot  or  the  bat's  wing,  be  adjusted  on  the  stage  of  a  microscope  for  direct 
inspection,  and  the  smaller  arterioles  are  under  observation,  then  upon  the 
stimulation  of  the  general  nerve  supplying  the  part  these  arterioles  will  sharply 
decrease  in  size.      In  fact  the  vaso-constriction  is  often  so  great  as  com- 


Fig.  203. — Plethysmogram  of  the  Hind  Limb  of  a  Cat,  showing  Vaso-constriction  upon  Stimu- 
lating the  Sciatic  64  times  per  second.     To  be  read  from  right  to  left.      (Bowditch  and  Warren.) 

pletely  to  occlude   the  vessel.     Very  soon  after  the  stimulation  the  vessel 
again  dilates  to  its  normal  size. 

The  presence  and  course  of  the  vaso-constrictor  nerve  supply  to  the 
organs  of  the  body  have  been  demonstrated  not  by  direct  inspection,  but 
by  the  use  of  various  forms  of  the  plethysmograph.  A  plethysmograph  is  an 
instrument  designed  to  measure  the  variations  in  the  volume  of  an  organ. 
If  the  finger,  the  whole  hand,  the  spleen,  or  the  kidney  be  placed  in  such  an 
instrument  and  the  proper  steps  be  taken  to  record  the  volume  changes,  it 
will  be  found  that  the  volume  of  the  enclosed  organ  is  constantly  changing 
with  every  variation  of  the  blood  pressure.  If  the  nerves  to  the  organ  are 
stimulated  by  the  usual  rapidly  interrupted  induction  current,  for  example, 
the  splanchnics  to  the  kidney,  then  there  is  a  decrease  in  the  volume  of  the 
organ.  This  decrease  takes  place  even  when  there  is  a  simultaneous  in- 
crease of  the  arterial  blood  pressure,  a  result  that  can  be  explained  only  on 
the  assumption  of  vascular  decrease  in  the  organ.  The  decrease  in  the  flow 
of  blood  to  the  specific  organ  can  be  induced  only  by  a  great  decrease  in  the 
size  of  the  arterioles  produced  by  contractions  of  the  circular  muscles  of 
their  walls. 


214 


THE     CIRCULATION     OF    THE     BLOOD 


Vaso-motor  Tone.  Vaso-constrictor  changes  are  constantly  occur- 
ring in  the  blood-vessels  of  the  organs  of  the  body,  a  fact  that  has  been 
abundantly  demonstrated  by  the  plethysmographic  experiments  just  men- 
tioned. Direct  inspection  of  the  ear  of  an  albino  rabbit  will  show  that  the 
arteries,  and  veins  as  well,  are  now  full  and  large  and  red,  and  the  interspaces 
filled  with  blood,  and  now  pale  and  constricted,  and  the  interspaces  apparent- 
ly bloodless.  If  the  cervical  sympathetic  is  cut  as  in  Bernard's  experiment, 
then  the  ear  vessels  remain  dilated,  that  is,  they  lose  their  tone,  showing 
that  the  condition  is  dependent  primarily  on  the  constant  discharges  cf  nerve 
impulses  from  the  nervous  system.  It  is  said  that 
the  vessels  regain  their  tone  after  a  time  when  the 
nerves  are  cut.  The  regained  power  may  be  ascribed 
to  the  muscle  fibers  themselves. 

Vaso-constrictor  Center.  "When  the  tonic  in- 
fluence exerted  by  the  nerve-fibers  on  the  arterioles 
is  traced  back  into  the  central  nervous  system,  it  is 
found  to  be  associated  with  the  activity  of  certain 
groups  of  nerve-cells,  or  centers,  which  are  called 
the  vaso-constrictor  centers.  This  determination  is 
made  in  part  by  the  method  of  sectioning.  A  lesion 
of  the  cerebro-spinal  axis  below  the  corpora  quad- 
rigemina  is  followed  by  partial  or  complete  general 
dilatation  of  the  blood-vessels  and  great  fall  of  blood 
pressure.  This  is  due  to  the  isolation  of  the  vaso- 
constrictor center,  which  lies  in  the  floor  of  the  fourth 
ventricle,  a  millimeter  or  two  caudal  to  the  corpora 
quadrigemina,  and  extends  longitudinally  over  an  area 
of  about  three  millimeters.  Owsjannikow  has  shown 
that  the  center  is  composed  of  two  halves,  each  half 
lying  in  the  lateral  column  to  the  side  of  the  median 
line.  This  center  is  in  constant  action  during  life, 
and  its  discharges  are  responsible  for  the  vascular 
tone  described  in  the  previous  paragraph.  The 
vaso-constrictor  center  varies  in  its  activity,  sometimes 
producing  wave-like  contractions  with  relaxations  of 
the  arterial  walls,  producing  variations  in  the  blood 
pressure  known  as  Traube-Hering  waves.  They  are 
more  often  observed  in  mammalian  blood-pressure 
experiments  after  prolonged  operations,  when  the  center  may  be  supposed 
to  be  itself  in  a  weakened  condition. 

Secondary  vaso-motor  centers  are  present  in  the  spinal  cord  as  proven 
by  Goltz.  Under  normal  conditions  they  do  not  act  independently  of  the 
medullary  center;  but  when  the  function  of  the  latter  has  been  interrupted 


GJb.s 


ETK?— 


en.p 


Fig.  204.  —  Diagram 
Showing  the  Paths  of  the 
Vaso-constrictor  Fibers 
along  the  Cervical  Sympa- 
thetic and  the  Abdominal 
Splanchnic.  Aur,  Artery 
of  ear;  G.Cs,  superior 
cervical  ganglion;  An.  V, 
annul  us  of  Vieussens;  G.St. 
stellate  ganglion;  D.I, 
D.I  I,  D.V,  thoracic  spinal 
nerves;  .46c?.  Spl.  abdomi- 
nal splanchnic.  The  arrows 
indicate  the  direction  of 
vaso-constrictor  impulse. 


VASOCONSTRICTOR     REFLEXES  215 

by  section  of  the  cord,  then  after  a  few  days  the  spinal  cells  below  the  section 
take  on  central  functions  and  bring  about  a  re-establishment  of  the  lost 
vascular  tone.  If  these  centers  be  destroyed  by  the  destruction  of  the  cord, 
then  the  tone  of  the  vessels  immediately  disappears  but  is  regained  after  the 
lapse  of  a  much  longer  time.  This  can  be  ascribed  to  the  presence  of  possi- 
ble sympathetic  constrictor  centers  or  more  probably  to  a  fundamental  prop- 
erty of  the  muscles  themselves.  This  experiment  was  carried  out  by  Goltz 
and  Oswald,  who  found  that  after  destruction  of  the  lower  pa-rt  of  the  spinal 
cord,  the  tone  of  the  vessels  of  the  hind  limbs,  lost  as  a  result  of  the  opera- 
tion,' was  later  re-established. 

Vaso- constrictor  Reflexes.  Under  normal  conditions  the  medul- 
lary center  responds  to  afferent  stimuli  by  vaso-motor  reflexes.  The  second- 
ary vaso-motor  centers  in' the  spinal  cord,  when  removed  from  the  influence 
of  the  bulbar  center,  can  and  do  respond  to  afferent  impulses  by  similar 
vaso-motor  action. 

The  afferent  impulses  which  excite  reflex  vaso-motor  action  may  proceed 
from  the  terminations  of  sensory  nerves  in  general,  or  possibly  from  the 
blood-vessels  themselves,  and  the  constriction  which  follows  generally  occurs 
in  the  area  whence  the  impulses  arise.  Yet  the  reflex  may  appear  elsewhere. 
Impulses  proceeding  to  the  vaso-motor  center  from  the  cerebrum  may  cause 
vaso-dilatation,  as  in  blushing,  or  vaso-constriction,  as  in  the  pallor  of  fear 
or  of  anger. 

Afferent  influence  upon  the  vaso-motor  centers  is  well  shown  by  the  action 
of  the  depressor  nerve,  the  existence  of  which  was  demonstrated  by  Cyon 
and  Ludwig.  The  depressor  is  a  small  afferent  nerve  which  passes  up  to 
the  medulla  from  the  heart,  in  which  it  takes  its  origin.  It  runs  upward  in 
the  sheath  of  the  vagus  or  in  the  superior  laryngeal  branch  of  the  vagus  or 
as  an  independent  branch,  as  in  the  rabbit,  communicating  by  filaments 
with  the  inferior  cervical  ganglion  as  it  proceeds  from  the  heart.  If,  in  a 
rabbit,  this  nerve  be  divided  and  the  central  end  stimulated  during  a  blood- 
pressure  observation,  a  remarkable  fall  of  blood  pressure  takes  place,  figure  205. 

The  cause  of  the  fall  of  blood  pressure  is  found  to  proceed  primarily 
from  the  dilatation  of  the  vascular  district  within  the  abdomen  supplied  by 
the  splanchnic  nerves,  in  consequence  of  which  the  vessels  hold  a  much 
larger  quantity  of  blood  than  usual.  The  engorgement  of  the  splanchnic 
area  very  greatly  diminishes  the  amount  of  blood  in  the  vessels  elsewhere, 
and  so  materially  diminishes  the  blood  pressure.  The  function  of  the  de- 
pressor nerve  is  that  of  conveying  to  the  vaso-motor  center  afferent  nerve 
impulses  from  the  heart,  which  produces  an  inhibition  of  the  tonic  activity 
of  the  vaso-motor  center  and,  therefore,  a  diminution  of  the  tension  in  the 
blood-vessels,  thus  relieving  the  heart  from  the  overstrain  of  propelling  blood 
into  the  already  too  full  or  too  tense  arteries.  It  has  been  shown  by  Porter 
and  Beyer  that  the  fall  in  blood  pressure,  following  stimulation  of  the  depres- 


216 


THE     CIRCULATION     OF    THE     BLOOD 


sor  nerve,  will  still  occur,  even  when  the  abdominal  vaso-constriction 
is  kept  constant  by  a  simultaneous  stimulation  of  the  splanchnics.  It  is 
therefore  evident  that  the  inhibitory  effect  of  depressor-nerve  stimulation  is 
a  general  one  and  not  confined  to  the  splanchnic  area  alone. 

The  action  of  the  depressor  nerve  in  causing  an  inhibition  of  the  vaso- 
motor center  illustrates  the  more  unusual  effect  of  afferent  impulses,  that  is, 
inhibition  of  the  vaso-constrictor  tone.  As  a  rule,  the  stimulation  of  the 
central  end  of  an  afferent  nerve,  such  as  the  sciatic  or  the  internal  saphenous, 
produces  the  reverse,  i.e.,  a  pressor  effect,  and  increases  the  tonic  influence 


iff 


Mao 


i  i  J  I  J  M  I  I  I  J  J  I  i  J  III  fi  l  I  H J  J  J  J  J  1  |  i  i  I  j  M  l  l  i  i  M  I  l  J  1  J  J  l  l  l  i  Mi  I  J  I  i 

Fig.  205. — Blood- Pressure  Record  (lower)  and  Respiratory  Record  (upper)  Obtained  from  a 
Dog  upon  Stimulating  the  Central  End  of  the  Divided  Vagus,  Both  Vagi  being  Cut.  The  marked 
fall  in  blood  pressure  is  due  to  the  effect  of  stimulating  the  depressor  fibers  contained  in  the  vagus 
trunk  of  the  dog.     (New  figure  by  Dooley  and  Dandy.) 

of  the  center  which  by  causing  constriction  of  the  arterioles  raises  the  blood 
pressure.  Thus  the  effect  of  stimulating  an  afferent  nerve  may  be  either 
to  constrict  or  to  dilate  the  arteries.  These  reflexes  may  be  general  enough 
to  influence  the  general  blood  pressure,  but  the  local  effects  are  the  all-im- 
portant ones,  since  by  these  the  local  regulation  of  the  blood  flow  is  accom- 
plished. 

Traube-Hering  Curves.  The  vaso-motor  center  sends  out  rhythmi- 
cal impulses  by  which  andulations  of  blood  pressure  of  a  large  and  sweeping 
character  are  produced,  quite  independent  of  the  so-called  respiratory  un- 
dulations. The  action  of  this  center  in  producing  such  undulations  is  de- 
monstrated in  the  following  observations.  In  an  animal  under  the  influence 
of  curari  and  with  both  vagi  cut,  and  a  record  of  whose  blood  pressure  is  being 
taken,  if  artificial  respiration  be  stopped,  the  blood  pressure  rises  sharply 
at  first.  After  a  time  the  rhythmical  undulations  shown  in  figure  206 
occur.  These  variations  are  called  Traube's  or  Traube-Hering  curves. 
There  mav  be  upward  of  ten  of  the  respiratory  undulations  in  one  Traube- 


VASO-DILATOR     NERVES 


217 


Hering  curve.  They  continue  until  the  vaso-motor  center  is  asphyxiated 
and  the  heart  exhausted,  when  the  pressure  falls.  The  undulations  cannot 
depend  upon  anything  but  the  vaso-motor  center,  as  the  mechanical  effects 
of  respiration  have  been  eliminated  by  the  curari  and  by  the  cessation  of 
artificial  respiration,  and  the  effect  of  the  cardio-inhibitory  center  has  been 
removed  by  the  division  of  the  vagi.  The  rhythmic  rise  of  blood  pressure 
is  most  likely  due  to  a  rhythmic  constriction  of  the  arterioles  followed  by  a 


Fig.  206. — Traube-Hering's  Curves.  (To  be  read  from  left  to  right.)  The  curves  1,  2,  3,  4, 
and  s  are  portions  selected  from  one  continuous  tracing  forming  the  record  of  a  prolonged  observa- 
tion, so  that  the  several  curves  represent  successive  stages  of  the  same  experiment.  Each  curve 
is  placed  in  its  proper  position  relative  to  the  base  line,  which  is  omitted;  the  blood  pressure  rises 
in  stages  from  1  to  2, 3,  and  4,  but  falls  again  in  stage  5.  Curve  1  is  taken  from  a  period  when  arti- 
ficial respiration  was  being  kept  up,  but,  the  vagi  having  been  divided,  the  pulsations  on  the  ascent 
and  descent  of  the  undulations  do  not  differ;  when  artificial  respiration  ceased,  these  undulations 
for  a  while  disappeared,  and  the  blood  pressure  rose  steadily  while  the  heart-beats  became  slower. 
Soon,  as  at  2,  new  undulations  appeared;  a  little  later,  the  blood  pressure  was  still  rising,  the  heart- 
beats still  slower,  but  the  undulations  still  more  obvious  (3);  still  later  (4),  the  pressure  was  still 
higher,  but  the  heart-beats  were  quicker,  and  the  undulations  flatter;  the  pressure  then  began  to  fall 
rapidly  (5),  and  continued  to  fall  until  some  time  after  artificial  respiration  was  resumed.  (M. 
Foster.) 


rhythmic  fall  of  pressure  and  relaxation,  both  being  due  to  the  action  of  the 
vaso-motor  center.  The  vaso-motor  center,  therefore,  is  capable  of  pro- 
ducing rhythmical  undulations  of  blood  pressure. 

Vaso-dilator  Nerves.  Claude  Bernard  discovered  that  the  blood 
flow  was  increased  through  the  salivary  glands  by  stimulation  of  the  nerves 
(the  chorda  tympani  for  the  submaxillary,  and  the  tympanic  branch  of  the 
glossopharyngeal  for  the  parotid),  thus  proving  that  the  arteries  have  not 


218  THE     CIRCULATION     OF    THE     BLOOD 

only  vaso-constrictors,  but  also  vaso-dilator  nerves.  Vaso-dilator  nerves 
have  been  described  for  most  parts  of  the  body.  In  general  they  are  dis- 
tributed in  the  same  nerve  trunks  which  bear  the  vaso-constrictors. 

It  is  not  supposed  that  the  vaso-dilators  produce  widening  of  the  arterioles 
by  stimulation  to  active  muscular  contraction;  in  fact  the  circular  arrange- 
ment of  the  muscle  fibers  would  seem  to  exclude  such  a  deduction.  It  is 
probable  that  there  is  local  inhibition  of  the  tonic  contraction  of  the  muscles, 
thus  allowing  the  mechanical  factor  of  the  general  blood  pressure  to  dilate 


Fig.  207. — Plethysmogram  of  the  Hind  Limb  of  a  Cat,  Showing  Vaso-dilatation  upon  Stimulating 
the  Sciatic  Once  per  Second.     To  be  read  from  right  to  left.      (Bowditch  and  Warren.) 

the  vessels.  The  vaso-dilator  nerves  are  characterized  by  their  response 
to  slowly  developed  stimuli,  shown  by  Bowditch  and  Warren,  and  by  the 
retention  of  irritability  after  degeneration  of  the  constrictors  has  taken  place, 
see  figure  207. 

Vaso-dilator  Centers.  No  distinct  medullary  center  has  yet  been 
shown  to  regulate  the  vaso-dilator  nerve  activity.  Such  centers,  if  they 
exist,  should  be  influenced  by  isolating  them  from  their  efferent  paths,  on 
the  one  hand,  or  by  stimulation  by  afferent  channels,  on  the  other.  The 
former  method  of  study  has  revealed  nothing  that  can  be  compared  to  the 
tonic  activity  of  the  constrictor  center.  Efferent  dilator-nerve  impulses  can 
be  reflexly  produced  by  sensory  stimulation.  The  isolated  lumbar  cord  of 
a  dog  is  capable  of  reflex  vaso-dilator  activity,  since  stimulation  of  the  skin 
of  the  penis  leads  to  reflex  vaso-dilatation,  indicating  the  presence  of  local 
vaso-dilator  centers  in  this  portion  of  the  spinal  cord. 

Vaso-dilator  Reflexes.  Perhaps  the  only  unquestioned  case  of 
reflex  vaso-dilatation  is  that  of  the  lumbar  cord  just  mentioned.  It  is  true 
that  many  apparent  reflexes  can  be  noted,  for  example  the  increased  flow 
of  blood  in  the  salivary  glands  under  gustatory  reflexes,  the  blushing  of  the 
skin  on  exposure  to  sudden  warmth,  or  even  the  blushing  of  emotional  origin, 
which  on  first  thought  might  be  regarded  as  vaso-dilator  reflexes.  But  each 
of  these  instances  can  be  just  as  readily  explained  as  inhibitions  of  the  vaso- 
constrictor tonic  activity.     This  double  explanation  can,  as  a  matter  of  fact, 


VASOCONSTRICTOR  AND  VASO-DILATOR  ACTIVITY  219 

be  applied  to  the  action  of  the  depressor  nerve  described  above,  page  217. 
On  the  whole,  however,  while  we  cannot  directly  and  unquestionably  prove 
the  fact,  yet  it  is  probable  that  each  of  the  above  examples  may  be  accepted 
as  examples  of  reflex  vaso-dilatation  by  direct  action  on  a  vaso-dilator  center 
or  centers  in  the  cord. 

The  Relation  of  Vaso- constrictor  and  Vaso-dilator  Activity.  The 
distribution  of  two  sets  of  regulative  fibers  for  the  muscular  walls  of  the 
blood-vessels,  when  considered  in  connection  with  the  other  factors  of  the 
vascular  apparatus,  gives  a  wonderfully  complete  mechanism  for  the  coordi- 
nation of  the  vascular  supply  with  the  activity  of  the  different  organs.  General 
and  broadly  distributed  activity  of  the  constrictors  produces  increase  of  general 
blood  pressure,  of  the  dilators  decrease  of  pressure,  but  local  activitv  of  either 
set  will  produce  a  great  reduction  or  increase  of  blood  in  the  local  organ 
with  little  or  no  effect  on  the  general  pressure.  When  a  vaso-dilatation  is 
produced  locally  in  one  organ  and  there  is  an  accompanying  vasoconstric- 
tion in  other  regions,  as  usually  happens,  it  is  evident  that  the  result  may  be 
a  flooding  of  the  local  region.  This  is  exactly  the  thing  that  is  accomplished 
in  the  muscles  in  violent  exercise,  in  the  glands  during  secretion,  in  the 
stomach  during  digestion.  It  is  this  mechanism  that  is  utilized  to  throw  a 
large  volume  of  blood  to  the  skin  when  the  temperature  of  the  body  is  above 
the  average,  or  to  blanch  the  skin  when  the  temperature  is  low. 

Normally,  certain  regions  of  the  body  are  associated  in  that  when  vaso- 
dilatation occurs  in  one  region,  vaso-constriction  occurs  in  the  other.  This  is 
particularly  true  with  the  skin  or  surface  of  the  body  and  the  viscera  or  deeper 
organs.  The  same  relation  is  said  to  exist  between  some  of  the  visceral 
organs. 

General  Course  of  the  Vaso- constrictor  and  Vaso-dilator  Nerves. 
The  cell  bodies  forming  the  medullary  vaso-motor  center  give  off  axones, 
axis-cylinder  processes,  some  of  which  go  to  the  nuclei  of  origin  of  certain 
cranial  nerves,  while  others  pass  down  the  cord  to  end  at  different  levels 
in  contact  with  certain  cells,  probably  small  cells  in  the  anterior  horn  and 
lateral  part  of  the  gray  matter.  These  cells  constitute  the  spinal  centers. 
The  neuraxones  of  the  spinal  cells  leave  the  cord  in  certain  spinal  nerves  in 
the  anterior  roots,  pass  by  the  white  rami  to  the  sympathetic  ganglion  chain, 
where  they  end  in  physiological  connection  with  the  ganglionic  cells.  Axones 
from  these  latter  cells  pass  by  an  uninterrupted  course  to  their  terminations 
on  the  blood-vessel  walls.  The  vaso-constrictor  fibers  leave  the  central 
nervous  axis  by  the  ventral  roots  of  all  the  dorsal  nerves  and  the  first  two 
lumbar  roots,  a  comparatively  restricted  region.  The  vaso-dilators  have 
the  same  origin  with  two  exceptions,  viz.,  the  vaso-dilators  of  the  salivary 
glands  found  in  the  seventh  and  ninth  cranial  nerves,  and  the  nervi  erigentes, 
which  arise  in  the  roots  of  the  second  and  third  sacrals.  The  nerves  to  the 
viscera  pass  direct  to  their  blood-vessels,  but  the  vascular  nerves  for  the  skin, 


220  THE     CIRCULATION     OF    THE     BLOOD 

muscles,  limbs,  etc.,  rejoin  the  main  divisions  of  the  spinal  nerves  through 
the  gray  rami,  see  figures  417  and  418,  and  pass  to  the  blood-vessels  along 
with  the  general  nerves  of  the  organ  or  organs. 

VASO-CONSTRICTOR    AND    VASO-DILATOR    NERVES     FOR    IN- 
DIVIDUAL ORGANS. 

The  particular  paths  for  the  vaso-motor  nerves  has  been  pretty  definitely 
established  by  numerous  researches,  especially  by  those  of  Langley  and 
his  students. 

The  course  of  the  vaso-constrictor  and  the  vaso-dilator  nerve  fibers  has 
been  followed  satisfactorily  in  many  of  the  important  parts  of  the  body, 
though  the  supply  for  some  regions  is  yet  obscure.  This  is  particularly 
true  for  the  brain,  where  such  supply  is  apparently  absent.  The  two  groups 
of  fibers  run  the  same  course,  except  in  the  cephalic  and  sacral  regions  already 
mentioned.     They  may,  therefore,  be  described  together. 

The  Vascular  Nerve  Supply  for  the  Head.  The  vascular  nerves 
for  the  head,  face,  and  mouth  have  their  origin  in  the  cord  from  the  first  to 
the  fifth  dorsal  spinal  nerves.  They  pass  through  the  white  rami  to  sym- 
pathetic ganglia,  through  the  stellate  ganglion  and  up  the  cervical  sympa- 
thetic nerve  to  the  superior  cervical  ganglion.  From  this  ganglion  they  run 
to  their  distribution,  either  along  with  the  arteries,  as  with  the  salivary  sup- 
ply, or  with  the  sensory  nerves,  as  in  the  nerves  to  the  mucous  membrane 
of  the  mouth,  etc.  The  vascular  nerves  supplied  to  the  base  of  the  ear  follow 
the  above  course,  but  the  nerves  for  the  tip  leave  the  stellate  ganglion  in  the 
ramus  vertebralis,  run  to  the  third  cervical  nerve,  and  pass  with  its  auricular 
branch  to  the  ear,  a  circuitous  route  determined  by  Fletcher. 

The  great  exception  to  the  above  origin  is  with  the  vaso-dilator  group. 
Dilator  fibers  leave  the  base  of  the  brain  in  the  direct  path  of  the  seventh 
cranial  nerve  to  supply  the  submaxillary  and  sublingual  glands,  in  the  ninth 
cranial  nerve  to  the  parotid  gland,  and  in  both  these  to  the  tongue. 

The  Vascular  Regulation  in  the  Brain.  The  brain  requires  a  large 
and  uniform  supply  of  blood  for  the  due  performance  of  its  functions.  This 
object  is  effected  through  the  number  and  size  of  its  arteries;  the  two  internal 
carotids,  and  the  two  vertebrals.  It  is  also  desirable  that  the  force  with 
which  this  blood  is  sent  to  the  brain  should  be  subject  to  less  variation  from 
external  circumstances  than  it  is  in  other  parts,  an  effect  that  is  accomplished 
by  the  free  anastomoses  of  the  large  arteries  in  the  circle  of  Willis.  This 
arrangement  insures  that  the  supply  of  blood  will  be  uniform  even  though 
it  may  be  limited  through  operation  or  accident  to  one  or  more  of  the  four 
principal  arteries.  Uniformity  of  supply  is  further  insured  by  the  arrange- 
ment of  the  vessels  in  the  pia  mater.  Previous  to  their  distribution  to  the 
substance  of  the  brain  the  large  arteries  break  up  and  divide  into  innumer- 


VASCULAR     REGULATION     IN     THE     BRAIN 


221 


able  minute  branches.  These  capillaries  after  frequent  communication  with 
one  another  enter  the  brain  in  a  very  uniform  and  equable  distribution. 
The  arrangement  of  the  veins  within  the  cranium  is  also  peculiar.  The  large 
venous  trunks  or  sinuses  are  formed  so  as  to  be  scarcely  capable  of  change 
of  size;  and  composed,  as  they  are,  of  the  tough  tissue  of  the  dura  mater, 
and  in  some  instances  bounded  by  the  bony  cranium,  they  are  not  com- 
pressible by  any  force  which  the  fulness  of  the  arteries  might  exercise  through 


Fig.  208. — Showing  the  Origin  and  Course  of  the  Vascular  Nerves  for  the  Head.      (Modified 

from  Moret.) 

the  substance  of  the  brain.     Nor  do  they  admit  of  distention  when  the  flow 
of  venous  blood  from  the  brain  is  obstructed. 

The  mechanical  conditions  in  the  brain  and  skull  formerly  appeared 
enough  to  justify  the  opinion  that  the  quantity  of  blood  in  the  brain  must 
be  at  all  times  the  same.  But  it  was  found  that  in  animals  bled  to  death 
without  any  aperture  being  made  in  the  cranium,  the  brain  became  pale  and 
anemic  like  other  parts.  And  in  death  from  strangling  or  drowning,  there 
was  congestion  of  the  cerebral  vessels;  while  in  death  by  prussic  acid,  the 
quantity  of  blood  in  the  cavity  of  the  cranium  was  determined  by  the  position 
in  which  the  animal  was  placed  after  death,  the  cerebral  vessels  being  con- 
gested when  the  animal  was  suspended  with  its  head  downward,  and  com- 


THE    CIRCULATION     OF    THE     BLOOD 

paratively  empty  when  the  animal  was  kept  suspended  by  the  ears.  Thus 
although  the  total  volume  of  the  contents  of  the  cranium  is  probably  nearly 
always  the  same,  yet  the  quantity  of  blood  in  it  is  liable  to  variation,  its  in- 
crease or  diminution  being  accompanied  by  a  simultaneous  diminution  or 
increase  in  the  quantity  of  the  cerebro-spinal  fluid.  The  cerebro-spinal 
fluid  being  readily  removed  from  one  part  of  the  brain  and  spinal  cord  to 
another,  and  capable  of  being  rapidly  absorbed  and  as  readily  effused,  would 
serve  as  a  kind  of  supplemental  fluid  to  the  other  contents  of  the  cranium 
to  keep  it  uniformly  filled.  Although  the  arrangement  of  the  blood-vessels 
insures  to  the  brain  an  amount  of  blood  which  is  tolerably  uniform,  yet  with 
every  beat  of  the  heart,  and  every  act  of  respiration,  and  under  many  other 
circumstances,  the  quantity  of  blood  in  the  cavity  of  the  cranium  is  con- 
stantly varying. 

The  brain,  however,  is  entirely  dependent  upon  the  general  blood  pres- 
sure for  variations  in  the  quantity  of  blood  which  it  receives.  During  a 
high  blood  pressure  the  amount  of  blood  that  flows  in  a  given  unit  of  time  is 
greater  and  during  low  blood  pressure  less.  Howell  has  shown  that  in  the 
decapitated  dog's  brain  the  flow  of  blood  is  directly  proportional  to  the  differ- 
ence in  pressure.  Numerous  attempts  have  been  made  to  show  vaso-motor 
mechanisms  for  the  cerebral  arteries,  but  without  success.  Huber  has  shown 
nerve  endings  in  such  arteries  by  histological  methods.  Bayless,  Hill,  and 
Gulland  make  the  statement  that  "  no  evidence  has  been  found  of  the  exist- 
ence of  cerebral  vaso-motor  nerves,  either  by  means  of  stimulation  of  the 
vaso-motor  center  or  central  end  of  the  spinal  cord,  after  division  of  the  cord 
in  the  upper  dorsal  region,  or  by  stimulation  of  the  stellate  ganglion,  and 
that  is  to  say  the  whole  sympathetic  supply  to  the  carotid  and  vertebral 
arteries."  Vaso-motor  regulation  of  the  flow  of  blood  through  the  brain 
can  be  accomplished  only  by  the  indirect  mechanism  of  regulation  of  general 
blood  pressure  through  variations  in  the  heart's  activity,  or  through  the 
effects  of  vaso-constrictions  or  dilatations  in  large  areas  other  than  the  brain. 

The  Vascular  Nerves  for  the  Thoracic  Viscera.  Numerous  efforts 
have  been  made  to  determine  the  vaso-motor  nerve  supply  for  the  thoracic 
organs,  the  heart  and  lungs.  In  the  heart  the  observation  is  rendered  com- 
plex by  the  fact  of  the  rhythmic  contractions  which  produce  mechanical 
pressure  on  the  coronary  arteries.  Martin,  by  direct  observation  through  a 
lens,  and  Porter,  by  measuring  the  outflow  of  the  coronaries  upon  vagus 
stimulation,  came  to  exactly  opposite  views;  the  former  that  the  vagus  con- 
tained vaso-dilators,  the  latter  that  it  contained  vaso-constrictors.  Still 
other  experiments  have  been  made  to  prove  either  constrictor  or  dilator 
nerves  for  the  coronary  arteries. 

The  lesser  circulation  through  the  lungs  has  also  proven  a  difficult  situa- 
tion to  interpret  as  regards  any  nervous  regulation  of  the  pulmonary  arterioles. 
The  evidence,  while  not  conclusive,  is  that  the  vaso-constrictor  supply  to  the 


VASCULAR    NERVES    FOR    THE    ABDOMINAL    VISCERA 


223 


lungs  is  from  the  third  to  the  fifth  thoracic  nerves,  but  that  the  vasoconstric- 
tion produced  is  slight  in  comparison  with  regions  of  the  systemic  circulation. 


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The  Vascular  Nerves  for  the  Abdominal  Viscera.  The  vasocon- 
strictors and  the  vaso-dilators  for  the  organs  of  the  abdominal  cavity  have 
a  broad  origin  in  the  cord;  from  the  first  dorsal  to  the  fourth  lumbar  in 
the  dog  and  cat.     The  nerves  pass  to  the  organs  by  the  splanchnic  nerves, 


224  THE     CIRCULATION     OF    THE     BLOOD 

and  by  the  solar,  celiac,  and  mesenteric  ganglia.     The  vascular  nerves  for 
the  different  organs  may  be  given  in  tabulated  form: 

Vascular  Nerves  jor  the  Abdominal  Viscera. 

Organ.  Spinal  Origin  of  the  Vascular  Nerves.  Course  to  the  Organ. 

Stomach  and  in-  i  _        T  (  Splanchnic     nerves     and 

testine.  \  5'  6'  7'  8'  9'  IO'  "•  I2'  I3°'    lL  '  '  *  '   '(     solar  and  celiac  ganglia. 

i   Splanchnic     nerves     and 
SPIeen 3,  4,  5.  6,  7,  8,  9,  io,  ii,  12,    13  D,   iL  >     sokr  and  celiac  ganglia. 


|     solar  and  celiac  gangli; 

\  Splanchnic      nerves     a 
\     solar  and  celiac  gangli, 

4,  ^,  6,  7,  8,  9,  io,  ii,  12,  13 D,  1,  2,  3,    (  Splanchnic      and      celiac 


Splanchnic      nerves     and 
Liver 3,  4,  5,  6,  7,  8,  9,  10,  11  D -      solarandceliac  ganglia. 


•    f       4L  j  ganglia. 

Inferior  splanchi 
ferior  mesenteric  ganglia. 


1  Inferior  splanchnic  and  in- 
Pelvic   viscera .  .  .  .  1,  2,  3,  4L < 


The  Vascular  Nerves  for  the  External  Genital  Organs.  The  vaso- 
dilators for  these  organs  arise  from  the  second  and  third  sacral  nerves  and 
pass  to  the  organs  by  the  nervi  erigentes  and  the  pelvic  plexus.  They  form 
the  second  great  exception  to  the  region  of  general  outflow  of  vascular  nerves. 
The  constrictors,  on  the  other  hand,  arise  in  the  spinal  nerves  from  the  last 
dorsal  and  first  four  lumbar.  They  run  the  same  course  as  given  in  the  table 
for  the  pelvic  viscera. 

The  greatest  variations  in  the  quantity  of  blood  contained  at  different 
times  in  the  external  genital  organs  are  found  in  certain  structures  which 
contain  what  is  known  as  erectile  tissue.  These  organs,  under  ordinary  cir- 
cumstances, are  soft  and  flaccid,  but  at  certain  times  they  receive  an  un- 
usually large  quantity  of  blood,  become  distended  and  swollen  by  it,  and 
pass  into  the  state  termed  erection.  Such  structures  are  the  corpora  cavernosa 
and  corpus  spongiosum  of  the  penis  of  the  male,  and  the  clitoris  in  the  female. 
The  nipple  of  the  mammary  gland  in  both  sexes,  and,  according  to  some 
authors,  certain  nasal  membranes  contain  erectile  tissue. 

The  corpus  cavernosum  of  the  penis,  which  is  the  best  example  of  an 
erectile  structure,  has  an  external  fibrous  membrane  or  sheath.  From  the 
inner  surface  of  the  sheath  numerous  fine  lamellae  project  into  the  cavity, 
dividing  it  into  small  compartments,  like  cells  when  they  are  inflated.  Within 
these  cells  there  is  a  plexus  of  veins  upon  which  the  erectile  property  of  the 
organ  mainly  depends.  The  plexus  consists  of  short  veins  with  very  close 
interlacings  and  anastomoses  with  very  elastic  walls  admitting  of  great  varia- 
tions in  size.  They  collapse  in  the  passive  state  of  the  organ,  but  are  capable 
of  an  amount  of  dilatation  which  exceeds  beyond  comparison  that  of  the  arteries 
and  veins  which  convey  the  blood  to  and  from  them.  The  strong  fibrous 
tissue  lying  in  the  intervals  of  the  venous  plexuses,  and  the  external  fibrous 
membrane  or  sheath  with  which  it  is  connected,  limit  the  distention  of  the 
vessels  and  give  to  the  organ  its  condition  of  tension  and  firmness.  The 
same  general  condition  of  vessels  exists  in  the  corpus  spongiosum  urethra?, 


VASCULAR    NERVES    FOR   THE    TRUNK    AND    LIMBS 


225 


but  the  fibrous  tissue  around  the  urethra  is  much  weaker  than  around  the 
body  of  the  penis,  while  around  the  glans  there  is  none.  The  venous  blood 
is  returned  from  the  plexuses  by  comparatively  small  veins;  all  of  which 
are  liable  to  the  pressure  of  muscles  when  they  leave  the  penis.  The  mus- 
cles chiefly  concerned  in  this  action  are  the  erector  penis  and  accelerator 
urinae.  Erection  results  from  the  distention  of  the  venous  plexuses  by  a 
sudden  influx  of  blood  resulting  from  the  action  of  the  nervous  vascular  re- 
flexes. It  is  facilitated  by  the  special  muscular  mechanism  which  prevents 
the  outflow  of  blood. 

The  Vascular  Nerves  for  the  Trunk  and  Limbs.  The  skin  and 
muscles  of  the  trunk  receive  their  cutaneous  and  motor  nerves  by  a  seg- 
mental arrangement  in  which  the  innervation  is  by  bands  corresponding 


Fig.  210. — Plan    of    Distribution  of  Vaso-constrictor  Nerves  for    the    Fore   Limbs.     An.    vi, 
Annulus  of  Vieussens.     (Modified  from  Moret.) 


with  the  segments  of  the  cord  and  the  spinal  nerves.  It  is  much  the  same 
with  the  vascular  nerves;  they  are  distributed  to  the  skin  and  walls  of  the 
trunk  in  the  same  segment  in  which  they  arise.  Langley  says  that  the  suc- 
cessive bands  overlap  somewhat. 

In  the  fore  legs  or  arms  the  vascular  nerves  arise  from  the  first  to  the 
fifth  dorsal  spinal  nerves,  run  to  the  stellate  ganglia,  then  by  the  gray  rami 
15 


226  THE     CIRCULATION     OF    THE     BLOOD 

back  through  the  ramus  vertebralis  to  join  those  cervical  nerves  that  enter 
into  the  brachial  plexus,  figure  210. 

The  nerves  for  the  blood-vessels  of  the  lower  limbs  arise  from  the  tenth 
dorsal  to  the  second  lumbar  nerves.  These  pass  to  the  ganglionic  chain, 
and  gray  rami  are  given  off  which  join  the  lumbar  plexus  and  run  with  the 
divisions  of  that  nerve  complex  to  their  distribution  in  the  skin  and  muscles. 
Vaso-constrictors  and  vaso-dilators  have  a  common  course  to  the  lower  limbs. 

The  Vaso- constrictor  Nerves  for  the  Veins.  Mall  has  proven 
that  vaso-constrictors  are  present  for  the  portal  vein.  These  fibers  are 
present  in  the  splanchnic  nerves.  Other  evidences  have  been  observed 
which  render  the  view  probable  that  vaso-motors  for  the  veins  in  general 
exist.  Hough,  for  example,  in  an  extended  study  of  the  capillary  pressure 
found  many  variations  which  were  readily  explained  only  on  the  assump- 
tion of  veno-motor  activity,  see  figure  201. 

LABORATORY  EXPERIMENTS  ON  THE  CIRCULATION. 

1.  The  Rate  of  the  Human  Heart-beat.  Determine  the  rate  of 
the  heart-beat  per  minute  by  counting  the  radial  pulse,  using  a  watch  for 
the  time.  Make  the  determination  after  sitting  quietly  in  a  chair  for  five 
minutes.  Take  the  average  of  at  least  ten  determinations  for  your  own  case. 
Determine  the  heart-rate  under  the  same  conditions  for  as  many  different 
persons  as  you  can.  Tabulate  these  determinations  in  a  table  which  shows 
age,  sex,  weight,  and  height  of  the  different  individuals,  and  compute  a 
general  average  for  your  entire  set. 

Note  the  effect  on  the  averages  obtained  above  after  the  person  lies  down 
for  five  minutes,  after  standing  quietly  for  the  same  time,  and  after  five  minutes' 
brisk  walk.     Tabulate  as  directed. 

Count  the  heart-rate  immediately  after  two  minutes'  fast  running,  allow- 
ing the  person  immediately  to  sit  in  a  chair.  Count  the  rate  by  two  minutes 
until  there  is  a  complete  return  to  the  normal,  as  determined  above.  Tabu- 
late these  results  and  compare  the  figures  obtained  from  several  different 
individuals. 

Count  your  own  heart-rate  at  intervals  during  one  entire  day,  giving 
special  attention  to  the  rate  just  before  and  just  after  meals,  but  in  every 
case  make  the  count  after  sitting  quietly  for  five  minutes.  A  marked  diurnal 
variation  will  usually  appear.  Determine  these  rates  on  several  individuals, 
and  tabulate  as  before. 

2.  Human  Cardiogram.  Apply  a  Burdon-Sanderson  cardiograph 
to  the  thorax  over  the  point  between  the  fifth  and  sixth  ribs  of  the  left 
side,  at  which  point  the  cardiac  impulse  is  felt  most  distinctly.  Connect 
the  cardiograph  with  a  recording  tambour,  Marey's  form,  adjust  the  tension 
of  the  cardiograph  and  the  pressure  of  the  air  within  the  system,  and  take  a 


THE     FROGS     HEART 


227 


tracing  of  the  movements  of  the  lever  of  the  recording  tambour  on  the  smoked 
paper  of  the  kymograph.  The  kymograph  cylinder  should  travel  at  the  rate 
of  about  two  to  three  centimeters  per  second.  Take  the  time  of  the  move- 
ments of  the  kymograph  by  means  of  an  electric  magnet  connected  with  an 
electric  clock  beating  seconds.  After  the  record  is  secured  the  proper  de- 
scription should  be  written  with  a  pencil  on  the  smoked  paper,  and  the  paper 
removed  from  the  kymograph  carefully  and  the  whole  record  fixed  in  shellac. 

When  the  record  is  dry,  count  the  rate  of  the  heart-beat  from  the  record 
and  measure  the  time  of  the  cardiac  systole  and  diastole,  and  the  time  of 
pause  at  the  end  of  the  diastole.  If  these  facts  are  taken  from  records  secured 
under  different  conditions  of  exercise,  etc.,  as  outlined  in  the  preceding  ex- 
periment, then  they  may  be  brought  together  in  a  table  for  convenience  of 
inspection.  A  comparison  of  such  results  will  usually  show  that  with  the 
higher  heart-rates  the  decrease  of  the  time  of  the  cardiac  cycle  is  at  the  ex- 
pense of  the  time  of  the  diastole;  in  other  words,  the  time  of  the  systole  re- 
mains fairly  constant  while  the  time  of  the  diastole  increases  or  decreases 
with  the  rate,  a  fact  to  which  Hiirthle  has  drawn  attention,  figure  157. 

3.  The  Rate  and  Sequence  of  the  Contractions  of  the  Frog's 
Heart.  Destroy  the  brain  of  the  frog  and  open  the  thorax,  but  do 
not  destroy  the  pericardium.     Count  the  rate  of  the  heart  per  minute,  then 


Fig.  an. — Heart  Lever  for  Frog  or  Turtle  Hearts. 


remove  the  pericardium  and  make  a  second  determination  after  the  heart  is 
exposed  to  the  air.  The  different  parts  of  the  heart  when  exposed  are  easily 
identified  and  the  contractions  which  take  place  in  definite  sequence  can  be 
determined  without  difficulty.  Make  this  determination  for  the  ventricle, 
auricle,  and  sinus  venosus  by  direct  observation. 


THE     CIRCULATION     OF    THE     BLOOD 


Prepare  a  cardiac  lever  as  shown  in  figure  211,  taking  special  care  to  ar- 
range the  foot  so  that  it  will  not  bind  on  the  lever  when  in  motion.  Adjust 
the  foot  of  the  lever  on  the  exposed  ventricle  and  bring  its  point  to  write  on 
the  smoked  paper  of  a  recording  cylinder.  This  cylinder  should  travel  at 
the  rate  of  about  1  cm.  per  second  and  its  speed  be  determined  by  the  writing 
point  of  an  electric  magnet  which  is  connected  with  the  electric-clock  circuit 
marking  seconds.  Take  care  to  adjust  the  time  magnet  in  a  vertical  line 
with  the  writing  point  of  the  heart  lever,  placing  the  heart  lever  about  1  cm. 
above  the  magnet  lever.  The  tracing  of  the  ventricle's  movement,  or  cardio- 
gram, will  show  alternate  contraction,  relaxation,  and  pause  of  the  ventricle. 
It  will  also  enable  one  to  measure  the  exact  proportion  of  the  total  time  of  the 


Fig.  212. — Cardiogram  Showing  Contractions  of  the  Auricle,  a,  and  Ventricle,  v,  of  a  Frog.     Time  in 
seconds.     The  record  shows  the  sequence  of  the  auricle  and  ventricle.      (New  figure  by  Dooley.) 

cardiac  cycle  consumed  by  the  systole  and  diastole,  and  also  that  portion  of 
the  diastole  in  which  the  ventricle  is  wholly  at  rest. 

After  one  has  obtained  the  ventricular  tracings  and  has  learned  the  diffi- 
culties of  adjusting  the  apparatus,  a  second  heart  lever  should  be  adjusted 
so  that  its  foot  rests  upon  the  auricle,  and  the  auricular  movements  may 
therefore  be  traced  on  the  smoked  paper  of  the  recording  cylinder  at  the  same 
time  as  those  of  the  ventricle.  If  some  care  is  taken  to  adjust  these  two 
writing  points  in  a  vertical  line  a  splendid  tracing  showing  synchronism 
between  auricle  and  ventricle  is  obtained.  Measure  the  rate  and  the  time 
of  the  different  phases  of  the  contraction  of  the  auricle  and  ventricle  and 
tabulate  them  in  the  following  form,  always  expressing  fractions  in  the 
decimal  svstem: 


Rate  per 
Minute. 

Time  of  Systole 
in  Seconds. 

Time  of  Diastole 
in  Seconds. 

Time  of  Pause 
in  Seconds. 

4.  The  Contractions  of  the  Excised  Heart  of   the  Frog.     Pith   a 
frog  and  expose  the  heart,  as  described  in  the  preceding  experiment.     Re- 


INFLUENCE    OF    DIFFERENT    NUTRIENT    FLUIDS  229 

move  it  completely  from  the  body  by  first  cutting  the  arteries  at  their  branch- 
ing in  front  of  the  bulbus  arteriosus,  then  carefully  lifting  up  the  parts  of 
the  heart  and  cutting  away  the  great  veins  where  they  enter  the  sinus.  This 
will  remove  the  entire  heart,  including  all  its  contractile  parts.  The  frog's 
heart  when  thus  removed  and  still  wet  with  its  own  blood  will  continue  con- 
tracting rhythmically  and  in  its  natural  sequence  for  some  hours.  Place 
such  an  isolated  heart  in  a  watch-glass  and  take  a  record  of  its  contractions, 
by  the  apparatus  described  in  the  preceding  experiment. 

Set  this  watch-glass  on  the  metal  warming-box  supplied,  and  arrange 
for  the  circulation  of  water  of  different  temperatures  through  the  box.  Vary 
the  temperature  of  the  box,  and  therefore  of  the  heart  placed  upon  it,  by 
allowing  water  of  o°  C,  io°  C,  200  C,  300  C,  400  C.  to  flow  through  it. 
Record  the  contractions  of  the  heart  at  each  of  these  temperatures  on  the 
recording  drum  as  described  in  experiment  3  above.  The  heart  being  ex- 
posed will  not  take  the  same  absolute  temperature  as  the  box,  but  the  relative 
temperature  will  be  decreased  or  increased.  Tabulate  the  rates  at  these 
different  temperatures  by  the  plan  previously  described. 

5.  The  Influence  of  Different  Nutrient  Fluids  on  the  Excised 
Heart.  Expose  a  frog's  heart,  as  previously  described,  and  insert  a  can- 
nula into  the  ascending  vena  cava  just  where  it  enters  the  sinus.  Ligate 
the  descending  vena  cava,  introduce  a  cannula  into  one  of  the  branches  of 
the  aorta,  and  carefully  separate  the  heart  from  the  body  without  injuring  its 
cavities  within  the  points  of  ligature.  Or  the  ligatures  may  be  laid  and  the 
cannula?  inserted  without  separating  the  heart  from  the  body.  Connect 
the  venous  cannula  with  a  Mariotte's  bottle  filled  with  physiological  saline, 
0.7  per  cent  sodium  chloride.  Adjust  the  constant  level  tube  for  a  pressure 
of  6  cm.  of  fluid  and  allow  the  saline  to  flow  through  the  heart.  The  arterial 
cannula  should  be  connected  with  a  short  rubber  tube  the  mouth  of  which 
allows  the  fluid  to  flow  into  a  beaker  or  glass  tumbler.  The  outlet  of  the 
arterial  tube  should  be  about  2  cm.  above  the  level  of  the  heart  so  that  the  heart 
must  work  against  a  slight  pressure.  The  heart  will  continue  its  contractions 
in  good  sequence  and  with  a  fairly  rapid  rate.  Record  the  contractions  on 
the  smoked  paper  of  the  recording  drum,  together  with  a  time  tracing  in 
seconds,  the  drum  traveling  at  the  rate  of  about  2  to  5  mm.  per  second. 

Use  the  tracing  obtained  under  the  influence  of  physiological  saline  solution 
as  a  normal  and  compare  with  it  the  rate  and  amplitude  of  the  contractions 
when  the  heart  is  perfused  with  Ringer's  solution;  with  Locke's  solution;  with 
saline  and  potassium  in  the  proportion  found  in  Ringer's  solution;  with 
saline  and  calcium  in  the  proportion  found  in  Ringer's  solution;  with  milk 
diluted  6  vols,  with  saline;  with  normal  serum  or  blood;  with  blood  or  serum 
diluted  four  times  with  saline.  Tabulate  the  rates  and  amplitude  of  the 
heart  under  these  different  influences  by  the  method  previously  followed. 

6.  The   Heart   Volume.     Isolate  a  frog's  heart  by  the  method  de- 


230 


THE     CIRCULATION    OF    THE     BLOOD 


scribed  for  irrigating  it  with  fluid  in  the  preceding  experiment.  Connect 
it  up  in  a  Roy's  tonometer,  see  figure  213,  adjust  the  lever  of  the  tonometer 
for  a  tracing  on  the  smoked  paper  of  the  recording  cylinder.  Use  a  time- 
marker.     This  instrument  records  the  change  in  volume  with  each  heart 


Fig.  213. — Roy's  Tonometer. 

contraction.     The  influence  of  pressure,  varied  between  2  and  10  cm.,  and  of 
nutrient  fluids  on  the  heart  volume  may  be  determined. 

7.  The  Isolated  Heart  of  the  Terrapin.  The  heart  of  the  terrapin, 
being  somewhat  larger  and  somewhat  more  responsive  than  the  heart  of  the 
frog,  may  be  substituted  in  the  two  immediately  preceding  experiments. 
The  facts  obtained  from  it  will  be  essentially  the  same  as  those  obtained 
from  the  frog's  heart. 

8.  The  Isolated  Mammalian  Heart.  The  mammalian  heart 
may  be  isolated  from  the  body  and  kept  alive  and  contracting  for  many 
hours,  as  has  been  demonstrated  by  numerous  recent  observations.  It  is 
only  necessary  to  keep  the  temperature  approximately  that  of  the  normal 
body  and  to  irrigate  the  heart  through  the  coronary  circulation  with  blood, 
or  diluted  blood,  containing  sufficient  hemoglobin  to  supply  the  heart  with 
the  requisite  amount  of  oxygen.  Or,  the  heart  may  be  kept  alive  on  the  inorganic 
salt  solutions,  provided  these  are  supplied  with  oxygen  under  considerable 
tension  (Porter,  Howell).  Even  the  human  heart  has  been  isolated  and 
kept  contracting  for  seme  hours  in  the  above  manner  (Kuliabko).  The 
method  used  is  to  insert  a  supply  cannula  into  the  aorta  and  irrigate  the  heart 
through  the  coronary  circulation,  as  described  by  Langendorff .  Many  in- 
teresting experiments  and  demonstrations  can  be  made  on  the  mammalian 


AUTOMATIC     CONTRACTIONS     OF    THE     CARDIAC     MUSCLE 


231 


heart,  but,  as  this  experiment  is  usually  a  demonstration  experiment,  the  detail 
of  procedure  is  left  to  be  supplied  by  the  demonstrator. 

9.  Automatic  Contractions  of  the  Cardiac  Muscle.  Isolated  por- 
tions of  the  dog's  ventricle  have  been  kept  in  rhythmic  contraction  by 
Porter,  but  the  best  laboratory  material  is  supplied  by  the  heart  of  the  terra- 
pin. Cut  a  strip  from  the  ventricle  of  the  terrapin  extending  around  its 
curved  apex,  as  shown  by  the  dotted  line  in  the  accompanying  figure,  214. 
Split  this  strip  longitudinally  into  two  parts,  each  of  which  will  then  be  about 
3  to  5  mm.  in  diameter.  Use  care  to  cut  smooth,  straight  strips.  Tie  a  silk 
thread  around  the  extreme  tips  of  each  end  of  the  strip,  tying  a  loop  of  about 
1  cm.  long  at  one  end,  and  about  10  cm.  long  at  the  other.  Suspend  the  strip 
over  a  glass  hook,  figure  215,  by  the  short  loop,  and  connect  it  with  a  heart 
lever  by  the  long  loop,  as  shown  in  the  same  figure.  Use  a  tension  of  one 
gram.  Contractions  of  this  strip  as  arranged  will  be  recorded  with  a  mag- 
nification of  about  five  and  with  the  upstroke  of  the  lever,  which  is  convenient 


Fig.  214. — Heart  of  the  Terrapin  to  Show  the  Method  of  Cutting  the  Apex  Strip.     V,  Ventricle; 
Au,  auricles;    Vc,  venas  cava;;   Ao,  aorta. 

for  reading  and  interpretation.  The  strip  may  be  kept  moist  with  physio- 
logical saline  in  a  specimen  tube  of  about  1  by  3  inches  in  size,  and  the 
arrangement  of  apparatus  figured  makes  it  possible  easily  and  quickly  to 
change  this  solution  for  any  other  that  may  be  desirable. 

Contractions  of  the  ventricular  strip  in  saline  usually  begin  in  from  10  to 
40  minutes  after  the  preparation  is  made  and  go  through  a  regular  sequence  of 
slight  increase  in  rate  and  amplitude  for  from  10  to  20  minutes,  followed  by 
a  very  constant  rate,  but  gradually  decreasing  amplitude  for  a  period  of  from 
2  to  3  hours,  figure  171. 

This  preparation  makes  possible  many  instructive  experiments  tending 
to  show  fundamental  properties  of  cardiac  muscle.     The  preparation  con- 


232 


THE     CIRCULATION     OF    THE     BLOOD 


tains  no  nervous  mechanism  and  its  behavior  may  be  safely  attributed  to 
the  muscle  substance  itself. 

Try  the  following  experiments:  Submit  the  strip  to  saline  solutions  of 
different  temperatures,  varying  through  steps  of  5  degrees  from  o°  C.  to 
400  C.  Try  the  effect  of  the  different  ingredients  in  Ringer's  solution;  com- 
bine potassium  with  saline,  figure  172;  calcium  with  saline,  figure  173;  and 
potassium,  calcium,  and  saline.  Also  try  Locke's  solution;  solution  of  blood 
diluted  with  saline;  solution  of  milk  with  saline  in  the  proportion  of  one 
part  milk  to  four  of  saline. 

Cut  and  mount  strips  from  the  auricle  and  from  the  sinus,  letting 
the  latter  extend  out  on  to  the  vena  cava.  In  these  last  preparations 
care  must  be  taken  to  balance  the  lever,  as  a  slight  overtension  paralyzes 
the  muscle.     Immerse  these  strips  in  pure  serum,  compare  their  behavior 


Fig.  215. — Arrangement  of  Apparatus  for  Studying  the  Contractions  of  the  Strip  of  the  Apex 

of  the  Ventricle. 


with  that  of  the  ventricle  in  pure  serum.  The  sinus  and  usually  the  auricle 
will  be  found  rhythmic  in  serum,  while  the  ventricle,  if  it  contracts  at  all, 
will  contract  with  a  very  slow  rhythm.  Often  there  is  a  distinct  progressive 
decrease  in  the  rhythm,  the  sinus  having  the  same  rhythm  as  the  whole  heart, 
the  auricle  a  considerably  slower  rhythm,  and  the  ventricle  with  a  very  slow 
rhythm  or  even  quiet.  The  sinus  preparation  will  show  beside  the  funda- 
mental rhythm  a  characteristic  slow  contraction  and  relaxation,  which  has 
been  described  as  tone,  figure  170. 

10.  Influence  of  the  Cardiac  Nerves  on  the  Frog's  Heart.  Care- 
fully pith  a  frog  so  as  not  to  break  the  blood-vessels  at  the  base  of  the  brain, 
and  thus  permit  the  loss  of  the  blood  of  the  animal.  Expose  the  heart  as 
previously  described,  make  a  cut  through  the  manubrium,  continue  it  through 


INFLUENCE  OF  THE  CARDIAC  NERVES  ON  THE  FROG  S  HEART 


233 


the  skin  and  muscles,  at  the  angle  of  the  jaw,  thus  exposing  the  vagus  nerve. 
The  vagus  runs  diagonally  downward  and  backward  along  the  edge  of  the 
delicate  muscle  toward  the  heart.  The  glossopharyngeal  is  just  in  front 
of  the  vagus  and  the  hypoglossal  just  behind  it.  The  latter  runs  parallel 
with  the  vagus  near  its  origin,  but  lower  down  turns  across  the  vagus  and  runs 
to  its  distribution  in  the  tongue  muscles.  These  two  nerves  serve  to  aid  the 
student  in  the  identification  of  the  vagus,  see  figure  216.  It  is  usually  better 
to  cut  the  hypoglossal  away,  and  also  to  cut  the  brachial  and  the  laryngeal 
nerves. 

Prepare  an  induction  coil,  see  Laboratory  experiments  on  muscle.  Use 
platinum  electrodes  of  the  Harvard  pattern,  set  the  coil  for  a  mild  stimulus  when 
tested  by  the  lips  or  the  tongue,  lift  up  the  vagus  gently  and  lay  it  on  the  platinum 
tips  of  the  electrodes,  taking  care  that  the  electrodes  do  not  come  in  contact 


Fig.  216. — Diagram  Showing  the  Relations  of  the  Vago-sym pathetic  Nerve  to  the  Heart,  in  the 
Frog.  Hy,  Hypoglossal;  Gl,  glosso-pharyngeal;  Lar,  laryngeal;  V,  vago-sym  pathetic;  H,  heart; 
L,  lung. 

with  the  adjacent  tissue.  Arrange  a  signal  magnet  as  shown  in  the  diagram, 
so  that  the  signal  magnet  and  the  stimulating  key  of  the  induction  coil  may 
be  closed  and  opened  at  the  same  instant.  When  all  is  ready  stimulate  the 
vagus  for  five  to  ten  seconds,  recording  the  time  with  the  signal  magnet  and 
allowing  the  record  to  continue  until  the  heart  has  returned  to  its  normal 
rate  and  amplitude.  Most  students  fail  in  this  experiment  by  not  allowing 
sufficient  time  in  the  record  for  a  normal  before  stimulation,  and  by  not 
allowing  sufficient  time  after  stimulation  for  a  return  to  the  normal.  It  will 
be  better  to  take  one  good  tracing,  showing  the  facts  of  the  experiment,  than 
several  partial  tracings,  none  of  which  are  complete.     With   these   sugges- 


234  THE     CIRCULATION     OF    THE     BLOOD 

tions  in  mind,  repeat  the  above  experiment,  using  stimulating  currents  of 
increasing  intensity  until  complete  cardiac  inhibition  is  produced.  Perform 
experiments  showing  the  influence  of  the  time  of*the  stimulus  on  the  inhibi- 
tion, i.e.,  stimuli  of  i  second,  2  seconds,  10  seconds,  and  30  seconds. 

In  the  frog  the  vagus  or  inhibitory,  and  sympathetic  or  accelerator  fibers, 
are  found  in  one  trunk,  the  vago-sympathetic,  but  the  stimuli  will  usually 
produce  inhibitions  and  not  acceleration.  Occasionally  with  very  weak 
preparations  direct  acceleration  may  be  produced.  To  get  the  pure  inhibi- 
tory or  pure  accelerator  effects  one  must  dissect  back  to  the  origin  of  the  vagus 
before  it  is  joined  by  the  sympathetic  fibers;  or  to  the  sympathetic  trunk 
between  the  third  spinal  nerve  and  the  point  where  it  joins  the  vagus  trunk. 
In  the  study  of  the  conditions  in  the  above  experiments  one  should  note 
the  rate  per  minute  and  the  amplitude  in  the  normal,  the  period  just  before 
stimulation,  the  rate  and  amplitude  during  the  period  of  stimulation,  and  the 
same  at  different  times  after  the  stimulation  until  constant  results  are  ob- 
tained. A  tabulation  of  these  results  will  usually  enable  one  to  judge  the 
influence  of  each  of  the  various  factors  recommended  in  the  experiment. 

11.  Influence  of  the  Cardiac  Nerves  on  the  Terrapin's  Heart. 
Instead  of  the  frog  one  may  use  the  terrapin  in  the  above  experiment. 
In  this  animal  the  sympathetic  can  very  readily  be  isolated,  and  accelerator 
fibers  have  been  described  for  it.  In  the  experience  of  the  laboratory  of 
the  author  no  experiments  have  yet  demonstrated  unquestionable  cases  of 
cardiac  acceleration.  The  vagus  produces  inhibitions  which  differ  from 
the  effects  in  the  frog  in  that  complete  inhibitions  of  the  ventricle  are  followed 
by  contractions  that  are  apparently  at  once  maximal.  In  the  frog  the  con- 
tractions when  they  reappear  are  at  first  slight,  but  gradually  increase  in 
amplitude  until  they  have  their  former  value. 

12.  The  Arterial  Blood  Pressure  in  a  Mammal.  The  arterial 
blood  pressure  may  be  measured  on  the  anesthetized  cat,  dog,  or  rabbit. 
Simple  blood  pressure  was  originally  measured  by  Hale's  method  of  connect- 
ing the  artery  with  a  vertical  tube  and  allowing  the  blood  to  flow  freely  into 
the  tube  until  a  column  was  raised  to  the  height  which  balanced  the  pressure 
in  the  vessel.  This  simple  method  is  decidedly  the  best  for  the  beginner, 
since  it  does  not  necessitate  the  use  of  very  complicated  apparatus.  At  the 
same  time  it  gives  practice  in  anesthesia  and  in  operations  of  vivisection, 
and  therefore  serves  as  a  good  preparation  for  the  more  complicated  ex- 
periments which  follow. 

The  necessary  apparatus  should  be  prepared  first,  as  follows:  A  vertical 
tube  supported  on  a  stand  with  a  scale  graduated  in  the  metric  system,  as- 
sorted cannula?  of  approximately  the  size  of  the  carotid  artery  of  the  animal 
to  be  operated  on,  linen  thread  ligatures,  dissecting  set  in  good  condition, 
an  animal-holder  with  strings  or  straps  firmly  to  fasten  the  anesthetized 
animal,  a  chloroform-ether  mixture  for  dogs  (or  other  anesthesia  according 


ARTERIAL    BLOOD    PRESSURE    IN   A    MAMMAL  235 

to  the  animal  to  be  used).  Four  men  should  be  assigned  to  perform  this 
experiment.  While  two  are  anesthetizing  and  preparing  the  animal,  two 
should  arrange  the  apparatus  as  nearly  ready  for  connecting  with  the  arterv 
as  possible.  When  all  the  apparatus  is  arranged  and  the  animal  anesthetized, 
it  should  be  tied  firmly  to  the  animal-holder.  Let  one  experimenter  attend 
strictly  and  at  all  times  to  anesthetizing  the  animal;  recovery  from  the 
anesthesia  must  not  occur.  Let  the  operator  quickly  expose  about  3  cm.  of 
the  carotid  artery  by  making  an  incision  through  the  skin  of  the  neck  5  cm. 
long,  and  dissecting  down  between  the  muscles.  Separate  the  carotid  from 
the  adherent  vagus  nerve  by  tearing  the  connective  tissue  with  the  scalpel 
handle,  freeing  the  vessel  from  about  2  to  3  cm.  of  its  length.  Lav  two  loose 
ligatures  of  linen  thread  around  the  vessel,  place  a  small  bulldog  forceps 
on  the  exposed  artery  nearest  the  heart,  and  ligate  the  end  nearest  the  head 
with  one  of  the  ligatures.  Take  up  the  intervening  artery  with  strong  forceps 
and  make  a  V-shaped  cut  near  the  ligature,  pointing  the  cut  toward  the  heart, 
and  letting  it  extend  about  half  way  across  the  artery.  Introduce  a  cannula 
through  the  opening  toward  the  heart,  and  tie  it  firmly  with  the  second  liga- 
ture.    Connect  the  cannula  with  the  rubber  tubing  to  the  vertical  glass  tube. 

When  all  is  ready  remove  the  bulldog  forceps  on  the  artery,  following 
which  the  blood  will  flow  freely  from  the  artery  into  the  tube  until  the  pressure 
from  the  column  of  liquid  is  just  equal  to  that  inside  the  artery  itself.  If  an 
anti-coagulating  fluid,  10  per  cent  magnesium  sulphate,  is  first  introduced 
into  the  vertical  tube  of  fortunate  height  little  blood  will  be  lost  and  probably 
clotting  at  the  cannula  will  be  delayed  for  some  minutes.  The  mounting 
of  the  blood  into  the  empty  tube  makes  indeed  a  more  striking  demonstration, 
but  it  has  the  disadvantage  of  quickly  forming  a  clot  which  stops  the  experi- 
ment itself. 

An  accurate  measure  of  the  height  of  the  top  of  the  column  above  the 
level  of  the  cannula  at  the  artery  represents  the  arterial  blood  pressure  in 
terms  of  blood,  or  of  10  per  cent  magnesium  sulphate.  The  specific  gravity 
of  magnesium  sulphate  is  1.030;  of  blood  1.056;  of  mercury  13.6.  Record 
the  pressure  you  obtain  in  terms  of  blood  and  of  mercury.  Note  also  the 
variations  in  pressure  and  account  for  the  rhythm  of  each.  There  will  be 
a  general  variation  of  pressure,  depending  upon  the  degree  of  anesthesia. 
If  anesthesia  is  light  and  muscular  movements  happen,  there  will  be  an  in- 
crease in  the  blood  pressure.  If  the  anesthesia  is  heavy,  then  the  blood  pres- 
sure falls.  These  points  of  variation  should  be  marked,  or  recorded  at  once  in 
note-books.  Make  full  notes  of  all  accessory  facts  which  would  aid  you  to 
explain  the  variation  in  blood  pressure,  such  as  size  of  the  animal,  rate  of  res- 
piration, rate  of  heartbeat,  the  variations  in  anesthesia,  the  presence  of  the 
reflexes,  etc.,  etc. 

Chloroform  the  animal  to  kill  it,  and  note  the  change  in  blood  pressure 
during  the  process 


236  THE     CIRCULATION    OF    THE    BLOOD 

13.  The  Circulation  Time.  The  circulation  time  is  most  satis- 
factorily determined  in  the  laboratory  by  introducing  a  saline  solution  of 
methylene  blue  into  the  jugular  vein  on  one  side.  Note  directly  the  time 
with  a  stop-watch  until  the  color  appears  in  the  jugular  artery  and  the  jugular 
vein  of  the  opposite  side. 

Anesthetize  a  cat  or  dog  with  a  chloroform-ether  mixture,  tie  it  on  the 
animal-holder  and,  when  the  eye  reflexes  are  lost,  expose  the  jugular  vein  on 
the  right  side,  the  carotid  artery  and  the  jugular  vein  on  the  left.  Fill  a 
2-cm.  hypodermic  syringe  with  1  per  cent  methylene  blue  in  physiological 
saline,  insert  the  needle  into  the  right  jugular  vein,  pointing  it  toward  the  heart. 
Lift  the  left  carotid  artery  and  place  under  it  a  strip  of  moist  white  paper 
2  cm.  wide;  prepare  the  left  jugular  vein  in  the  same  way.  Place  the  animal 
so  that  these  vessels  are  lighted  to  the  best  advantage.  At  a  given  moment 
inject  the  contents  of  the  hypodermic  syringe,  noting  the  time  with  a  stop- 
watch. Observe  the  color  of  the  left  carotid  and  the  left  jugular,  respec- 
tively, very  carefully,  and  take  the  time  when  the  first  appearance  of  the 
methylene  blue  is  noted.  The  color  will  appear  first  in  the  artery,  second 
in  the  vein.  The  difference  in  time  between  the  moment  of  injection  and 
the  moment  of  color  in  the  artery  represents,  with  a  slight  correction,  the 
circulation  time  of  the  pulmonary  or  lesser  circulation.  The  time  from  the 
injection  until  the  color  in  the  jugular  vein  represents  the  total  time  of  circu- 
lation. 

Stewart  has  made  these  determinations  even  more  correctly  by  the  elec- 
trical-resistance method.  He  injected  10  per  cent  salt  solution  and  deter- 
mined the  variation  in  resistance  by  a  galvanometer.  If  the  galvanometer 
is  available,  then  check  the  above  determinations  by  the  electrical  method, 
arranging  the  apparatus  under  the  direction  of  an  instructor. 

14.  The  Blood-Pressure  Model.  An  artificial  model  of  the  cir- 
culatory apparatus,  which  illustrates  all  mechanical  parts  involved,  has 
been  arranged  by  Porter,  figure  217.  Other  forms,  which  show  these  as  well, 
are  usually  available  or  can  be  easily  constructed.  The  model  should  have 
the  following  possibilities:  A  pump,  which  permits  of  rhythmic  action  at  a 
varying  rate  and  varying  force;  a  resistance  to  the  outflow  liquid,  which  can 
be  increased  or  decreased;  and  an  elastic  set  of  vessels  into  which  the  pump 
discharges. 

If  Porter's  schema  is  used,  determine  the  following  points:  The  pressure 
in  terms  of  mercury  in  the  arterial  and  venous  limbs  of  the  apparatus  when  the 
pump  makes  a  rate  of  72  per  minute;  the  influence  on  these  two  pressures 
when  the  rate  is  increased,  when  it  is  decreased;  the  effect  on  these  pres- 
sures when  the  peripheral  resistance  is  great,  when  it  is  low.  If  a  sphygmo- 
graph  is  available,  take  a  tracing  of  the  pulse  in  the  elastic  tube  representing 
the  arterial  side  of  the  schema. 

If  an  ordinary  bulb  syringe  and  simple  apparatus  is  used,  then  deter- 


THE     ARTERIAL     PULSE  237 

mine  the  following:  The  character  and  rate  of  the  outflow  when  water  is 
pumped  into  the  rigid  glass  tube  with  no  resistance  to  the  outflow;  when  a 
glass  tube  of  smaller  caliber  is  connected  with  the  end  of  the  larger  glass 
tube  so  as  to  produce  a  high  resistance  to  the  outflow.  Pump  the  water  into 
a  rubber  tube  of  smaller  size  and  compare  with  the  proceeding  in  which 
there  is  no  resistance  to  the  outflow;  also  when  a  glass  tube  of  small  caliber 
is  introduced  into  the  end  in  order  to  produce  high  resistance  to  the  outflow. 
Determine  the  amount  of  resistance  necessary  to  produce  a  constant  out- 
flow when  the  pump  has  a  rate  of  72  beats  per  minute.  In  this  experiment 
what  effect  is  produced  on  the  outflow  if  you  vary  the  rate  of  the  pump  ?  if 
you  vary  the  force  of  the  stroke?  if  you  vary  the  elasticity  of  the  rubber 
tube  representing  the  artery  ?  if  you  vary  the  resistance  represented  by  the 
size  of  the  glass  tube  at  the  outflow  ? 

15.  The  Arterial  Pulse.  The  form  of  the  arterial  pulse  may  be 
taken  by  one  of  the  various  sphygmographs  applied  to  the  radial 
artery  at  the  wrist  or  the  common  carotid  in  the  neck.  If  the  tambour 
method  is  used,  apply  a  sphygmograph  tambour  on  the  wrist  with  the  central 
pressure  over  the  radial  artery.  Fasten  it  in  place  by  the  proper  bands, 
adjusting  the  tension  by  flexing  the  wrist.  Connect  the  receiving  tambour 
with  a  delicately  balanced,  small-sized  recording  tambour,  which  should 
write  its  movements  on  a  cylinder  revolving  at  the  rate  of  i  to  2  cm. 
per  second. 

A  more  convenient  clinical  instrument  is  the  Dudgeon  or  the  Jacquet 
sphygmograph.  These  are  to  be  applied  at  the  wrist  and  give  tracings 
showing  delicate  variations  in  the  form  of  the  pulse  wave  with  great  magnifi- 
cation and  a  considerable  degree  of  accuracy.  Make  a  comparison  of  the 
form  of  the  pulse  wave  from  tracings  taken  from  at  least  six  different 
individuals. 

The  sphygmogram  from  the  carotid  artery  may  best  be  taken  by  apply- 
ing a  tambour  sphygmograph  to  the  neck  over  the  carotid  and  fastening  it 
in  position,  usually  by  a  spring. 

16.  The  Rate  of  Propagation  of  the  Pulse  Wave.  Apply  tambour 
sphygmographs  to  the  carotid  in  the  neck  and  to  the  radial  at  the  wrist,  and 
make  simultaneous  record  on  a  recording  drum,  adjusting  the  writing  levers 
of  the  two  recording  tambours  in  an  exact  vertical  line.  Let  the  recording 
drum  travel  at  the  speed  of  2  cm.  or  more  per  second,  and  record  the  speed 
by  a  50  double-vibration  tuning-fork.  The  carotid  pulse  will  be  found  to 
precede  the  radial  pulse  by  the  fraction  of  a  second.  This  short  interval, 
which  can  be  determined  in  hundredths  of  a  second  by  comparison  with  the 
time  tracing  below,  represents  the  time  required  for  the  pulse  wave  to  travel 
the  distance  from  the  carotid  to  the  radial.  Measure  the  distance  on  the 
individual  used  in  the  experiment  and  calculate  the  rate  of  propagation  of 
the  pulse  wave  in  centimeters  per  second. 


238  THE    CIRCULATION     OF    THE     BLOOD 

If  the  writing  points  of  the  recording  levers  in  this  experiment  are  made 
of  very  delicate  strips  of  note  paper,  so  as  to  offer  little  resistance  to  the  sur- 
face of  the  drum,  the  detail  of  the  pulse  wave  at  the  two  points  will  be 
accurately  transcribed  and  may  be  compared. 

17.  The  Capillary  Circulation.  The  capillary  circulation  is  best 
demonstrated  in  the  laboratory  by  direct  observation  on  the  web  of  the  frog's 
foot  by  the  use  of  the  compound  microscope.  Give  a  40-gram  frog  a  hypo- 
dermic injection  of  0.3  c.c.  of  ether  under  the  skin  of  the  back.  Wet  a  piece 
of  cheese  cloth  the  size  of  a  handkerchief  with  tap  water  and  wrap  the  etherized 
frog  so  as  to  cover  the  entire  body  with  the  exception  of  the  foot.  When  the 
anesthesia  has  progressed  so  as  to  destroy  voluntary  movements,  bind  the 
foot  on  an  ordinary  frog  board  and  spread  the  web  over  the  window  in  the 
board.  Choose  an  area  of  the  skin  which  shows  small  arteries,  capillaries, 
and  veins,  and  in  which  the  blood  is  flowing  freely  and  rapidly.  Examine 
with  a  low-power  compound  microscope.  In  a  favorable  field  small  arteries, 
capillaries,  and  veins  with  blood  flowing  rapidly  through  them  will  be  easily 
found.  Choose  one  such  field,  cover  with  a  piece  of  thin  cover  glass,  moisten- 
ing with  a  drop  of  water  if  necessary,  and  examine  with  a  high  power.  Note 
in  the  small  artery  the  pulsating  current;  the  border  of  clear  fluid  along  the 
side  of  the  main  stream  of  blood;  the  slight  pulsations;  and  the  white  cor- 
puscles that  will  be  found  flowing  along  the  borders  of  the  current.  In  the 
small  veins  there  are  usually  no  pulsations  and  the  speed  of  the  current  is 
somewhat  less.  In  the  capillaries  a  careful  examination  will  reveal  a  deli- 
cate wall,  the  individual  corpuscles,  and  the  fact  that  the  red  corpuscles  are 
actually  larger  than  the  diameter  of  the  capillary  at  some  points  and  must 
be  bent  to  pass  through.  Note  that  the  capillaries  form  an  intricate  and 
anastomosing  network;  that  the  current  may  occasionally  reverse  itself  in 
some  of  the  anastomoses. 

The  anesthetizing  effect  of  the  dose  of  ether  recommended  will  usually  con- 
tinue about  15  to  20  minutes.  If  the  observation  is  more  prolonged  a  second 
dose  of  ether  should  be  given.  The  capillaries  in  the  tails  of  small  fish  are 
often  very  readily  observed  and  these  may  be  substituted  for  the  frog's  web. 

18.  Capillary  Blood  Pressure.  Measure  the  capillary  blood  pres- 
sure in  your  own  finger  by  von  Krie's  method.  This  apparatus  consists 
of  a  small  piece  of  glass  an  inch  square,  or  less,  which  is  placed  across  the 
knuckle  of  the  finger  just  back  of  the  nail.  A  small  weight  pan  is  suspended 
by  a  loop  of  thread  over  this  glass  plate  so  that  weights  put  in  the  pan  will 
bring  varying  pressure  on  the  plate  above.  Add  weights  to  the  pan  until 
an  area  of  the  skin,  about  5  mm.  in  diameter,  is  blanched  by  the  pressure. 
Mark  the  outline  of  this  bloodless  area  on  the  glass,  take  off  the  apparatus 
and  measure  the  exact  area  of  glass  so  marked,  weigh  the  entire  apparatus 
and  compute  the  pressure  per  square  centimeter  for  the  area.  This  pres- 
sure in  terms  of  mercury  represents  the  capillary  blood  pressure  in  the  vessels 


BLOOD    PRESSURE    IN    A    MAMMAL    AND    ITS    REGULATION  239 

of  the  skin  of  the  finger  at  that  level.  Vary  the  experiment  by  measuring 
the  pressure  with  the  finger  held  at  the  level  of  the  top  of  the  head;  with  the 
finger  held  as  low  as  possible;  held  at  the  level  of  the  heart.  Tabulate  the 
measurements.  The  capillary  blood  pressure  at  the  level  of  the  heart  is 
usually  from  40  to  50  mm.  of  mercury. 

19.  The  Arterial  Blood  Pressure  in  a  Mammal  and  Its  Nervous 
Regulation.  After  the  student  has  measured  the  arterial  blood  pres- 
sure by  Hale's  method,  described  above,  he  is  in  a  position  to  study  the 
variations  and  coordinations  in  the  blood  circulatory  apparatus.  The  re- 
cording apparatus  consists  of  writing  pens,  seconds  time  marker,  signal  marker, 
blood-pressure  manometer  preferably  Ludwig's  mercury  manometer,  and 
a  continuous  paper  kymograph  preferably  Ludwig's  weight-driven  form 
for  a  continuous  record  of  the  arterial  blood  pressure.  Connect  the  cannula 
with  the  mercury  manometer  which  is  provided  with  a  pressure  bottle. 
Use  a  cannula  of  the  form  shown  in  figure  185,  connecting  the  side  limb  of 
the  cannula  with  the  mercury  manometer,  and  the  end  limb  with  the  pressure 
bottle.  When  the  apparatus  is  ready  anesthetize  a  mammal  (dog,  cat,  or 
rabbit),  and  bind  it  down  to  the  animal-holder.  Let  one  operator  attend 
strictly  and  at  all  times  to  the  anesthetic,  for  the  animal  must  not  under  any 
condition  recover  consciousness  during  the  experiment. 

Expose  the  carotid  artery  in  the  neck,  as  described  in  experiment  12  above, 
arrange  it  with  ligatures  for  inserting  the  cannula,  expose  the  vagus  nerve 
with  the  same  care,  and  throw  ligatures  around  it  for  convenience  in  lifting 
it  out  of  its  bed.  Make  in  the  carotid  a  V-shaped  cut  directed  toward  the 
heart,  insert  and  ligate  the  cannula  as  previously  described.  Before  begin- 
ning the  experiment  one  should  see  that  all  the  tubes  are  filled  with  the  anti- 
coagulating  liquid  and  that  the  manometer  is  under  pressure  from  100  to 
150  mm.  mercury.  When  all  is  ready  start  the  kymograph,  ink  the  recording 
pens,  see  that  they  are  recording  properly  and  that  the  adjustments  are  se- 
cured, remove  the  bulldog  forceps  from  the  artery,  and  the  pressure  record 
begins. 

1.  Take  a  tracing  of  the  normal  arterial  pressure  and  heart  rhythm  with 
the  recording  paper  moving  at  the  rate  of  0.5  cm.  per  second. 

2.  Stimulate  the  vagus  nerve  with  a  mild-strength  induction  current. 
If  this  stimulus  is  strong  enough  to  produce  change  in  blood  pressure  or  in- 
hibitions of  the  heart  rate,  then  allow  sufficient  time  following  the  stimulus 
for  the  blood  pressure  to  return  to  the  previous  normal.  Observing  these 
rules,  vary  the  intensity  of  the  stimulus  from  that  which  produces  no  ap- 
parent effect  to  that  which  produces  complete  inhibition  of  the  heart.  Vary 
the  time  of  the  stimulus  from  1  to  10  seconds,  using  different  strengths. 

3.  Allow  the  vagus  to  fall  back  in  its  warm  bed  and  stimulate  the  skin 
of  the  animal  at  some  sensory  surface,  say  the  lips,  the  ear,  or  the  foot.  By 
varying  the  intensity  of  the  stimulus,  a  strength  will  be  found  which  will 


240  THE     CIRCULATION     OF    THE    BLOOD 

produce  no  reflexes  of  the  voluntary  muscles,  but  which  will  produce  marked 
effects  on  the  heart  rate  and  on  the  blood  pressure.  Expose  the  sciatic  nerve, 
or  any  other  general  nerve  trunk,  cut  it,  and  stimulate  the  central  end  for  5 
seconds.  With  a  proper  strength  of  stimulus  a  greater  effect  is  produced  on 
the  heart  and  on  the  blood  pressure  than  by  stimulating  a  small  spot  of  skin. 

4.  Cut  the  right  vagus  nerve  and  mark  the  exact  time  on  the  tracing  by 
the  signal  marker.  After  10  to  15  seconds  cut  the  left  vagus,  marking  the 
time  of  cutting  with  the  same  care  on  the  tracing.  As  soon  as  the  nerves  are 
cut,  the  heart-rate  will  be  observed  to  increase  sharply  and  the  blood  pressure 
to  rise.  The  respirations  also  change  in  rate  and  depth,  a  fact  which  can 
be  noted  on  the  blood-pressure  tracing.  Do  not  disturb  the  animal  or  record 
until  stable  equilibrium  is  again  reached. 

5.  Now  lift  up  the  distal  end  of  the  divided  vagus,  and  stimu- 
late it  with  an  electric  current  of  the  strength  which  previously  just 
produced  inhibition.  Repeat  the  experiment  on  the  proximal  end  of  the 
divided  vagus.  The  stimulation  of  the  proximal  end  of  the  vagus  produces 
no  direct  effect  on  the  heart  rate  when  both  vagi  are  cut,  but  does  produce 
profound  changes  on  the  blood  pressure  owing  to  vaso-motor  effects. 

6.  If  the  rabbit  is  used,  stimulate  the  depressor  nerve,  which  produces 
marked  fall  in  blood  pressure  from  reflex  effects. 

7.  Repeat  the  stimulation  of  the  central  end  of  the  sciatic  as  described 
in  3,  now  that  the  vagus  nerves  are  cut.  The  stimulation  of  this  nerve  no 
longer  produces  changes  in  the  heart-rate,  but  the  blood  pressure  is  influenced 
as  before,  showing  that  the  vaso-motor  centers  are  reflexly  stimulated. 

8.  When  you  have  finished  the  outline  of  experiments,  give  an  excess  of 
the  anesthetic  to  kill  the  animal  and  continue  the  record  until  the  animal  is 
dead.  The  blood  pressure  will  fall  rapidly,  the  heart-rate  will  become  slower 
but  does  not  cease  for  a  long  time. 

Should  a  clot  form  in  the  cannula,  put  a  bulldog  forceps  on  the  artery, 
disconnect  the  manometer  tube,  and  wash  the  clot  out  by  a  stream  of  liquid 
from  the  pressure  bottle.  Use  care  not  to  allow  this  fluid  to  enter  the  ex- 
posed wound. 

Represent  the  results  of  each  individual  experiment  in  the  above  series 
in  tabulated  form  which  shall  show  1,  the  blood  pressure  and  heart  rate 
just  before  each  experiment;  2,  during  the  experiment;  and  3,  at  different 
times  after  the  experiment  until  the  normal  is  reached.  After  the  facts  are 
taken  from  the  tracings  and  arranged  in  tabular  form,  make  a  study  of  these 
facts  and  draw  all  the  conclusions  you  can  concerning  the  nervous  regula- 
tions of  the  heart  and  of  the  blood  pressure. 

20.  Arterial  Blood  Pressure  in  Man.  The  arterial  blood  pressure 
in  man  can  be  measured  only  indirectly  by  measuring  the  pressure  which  it 
takes  around  the  arm  completely  to  close  the  artery.  Some  form  of  the 
Riva-Rocci    apparatus,    preferably    Erlanger's    sphygmomanometer,   should 


VASO-MOTOR    CHANGES     IN    THE     FINGER  241 

be  used.  Adjust  the  rubber  bag  and  leather  sleeve  of  the  Erlanger  appara- 
tus, figure  189,  to  an  arm,  and  connect  it  to  the  sphygmomanometer,  set  the 
valve  and  quickly  pump  the  pressure  up  to  a  point  which  occludes  the  pulse. 
Adjust  the  writing  point  of  the  recording  tambour  to  the  smoked  paper  on 
the  cylinder,  then  lower  the  pressure  by  io-mm.  steps  until  the  first  pulse 
appears.  Now  proceed  with  care,  changing  the  pressure  by  5-ram.  steps 
until  a  record  has  been  obtained  which  passes  the  maximal  amplitude.  Now 
release  the  pressure  from  the  arm.  The  first  point  in  the  decreasing  pressure 
at  which  the  pulse  tracing  begins  to  increase  is  known  as  the  systolic  pres- 
sure; the  point  in  the  pressure  which  records  the  highest  point  in  the  ampli- 
tude of  the  pulse  wave  is  known  as  the  diastolic  pressure.  The  systolic 
pressure  will  vary  from  120  to  150  mm.  of  mercury;  the  diastolic  from  90  to 
120  in  different  individuals  of  the  average  physiology  class. 

21.  The  Vaso-motor  Changes  in  the  Finger,  the  Plethysmogram. 
Insert  the  finger  in  the  Porter  finger  plethysmograph,  fill  the  tube  with 
water,  and  connect  it  with  a  small-sized  air  tambour.  The  variations  in 
volume  of  the  finger  are  slight,  so  that  one  must  use  a  rather  long,  delicately 
balanced  recording  lever.  Take  a  tracing  on  a  recording  cylinder  moving 
at  a  slow  speed,  1  mm.  per  second.  The  finger  and  its  plethysmograph 
should  be  supported  by  a  swinging  support  so  that  no  mechanical  move- 
ments will  destroy  the  accuracy  of  the  record.  Observations  through  several 
minutes  will  usually  show,  variations  in  volume  of  the  finger,  which  will  be 
recorded  by  the  tambour.  Cold  air  in  the  face  or  cold  water  on  the  hand 
will  usually  be  marked  by  a  decrease  in  volume  indicating  vaso-constriction. 
Application  of  heat  to  other  fingers  of  the  same  hand  will  lead  to  in- 
crease in  volume. 

22.  The  Vaso-motors  of  the  Frog's  Web.  Prepare  a  frog  for  ob- 
servation of  the  circulation  of  the  web  under  the  microscope,  as  described 
above;  but  give  it  just  enough  1  per  cent  curari  to  destroy  voluntary  move- 
ments. Quickly  dissect  the  sciatic  nerve  in  the  thigh,  using  extreme  care 
not  to  interfere  with  the  circulation.  Mount  the  preparation,  pick  out  an 
active  field  of  capillaries,  small  arteries,  and  veins  with  the  low  power  of  the 
microscope,  then  adjust  the  high  power  to  a  field  which  shows  one  or  more 
small  arteries.  Make  a  drawing  of  a  diameter  of  these  arteries,  using  pig- 
ment cells  for  land-marks.  Now  quickly  stimulate  the  exposed  sciatic  nerve 
while  keeping  the  selected  artery  under  constant  observation.  After  a  short 
stimulation  the  diameter  of  the  vessels  will  be  seen  to  decrease  considerably, 
sometimes  to  the  point  of  complete  occlusion.  When  the  stimulation  ceases, 
the  vessel  will  remain  contracted  for  a  few  seconds,  then  will  slowly  regain 
its  usual  caliber,  figure  201 .  This  is  an  exceptionally  good  method  for  direct 
observation  of  the  vaso-motor  changes  in  the  smaller  vessels. 

23.  The  Plethysmogram  of  the  Kidney.  Anesthetize  a  dog  or  cat, 
see  experiments  12  and  19  above,  and  take  blood-pressure  tracings  on  the  con- 

16 


THE     CIRCULATION    OF    THE    BLOOD 

tinuous-paper  kymograph.  Now  open  the  abdominal  wall  by  an  incision 
along  the  median  line,  expose  the  left  kidney  and  carefully  dissect  off  its  cap- 
sule, taking  care  not  to  injure  its  artery  and  vein.  Enclose  the  kidney  in 
the  renal  onkometer,  fill  the  onkometer  with  oil,  and  connect  it  with  a  record- 
ing apparatus.  Brodie's  bellows  recorder  is  probably  the  best  recording 
apparatus  for  this  purpose.  Adjust  the  recording  apparatus  in  the  vertical 
line  with  the  manometer  and  signal  pens. 

Stimulation  of  the  nerves  which  affect  the  general  blood  pressure  through 
the  medium  of  the  heart  will  be  found  to  produce  changes  in  the  volume  of 
the  kidney  in  the  same  direction  as  the  blood-pressure  change.  On  the 
other  hand,  stimuli  which  give  variations  of  the  blood  pressure  without 
direct  change  in  the  heart  itself  affect  the  volume  of  the  kidney  independent 
of  the  blood  pressure: 

i.  Dissect  out  and  stimulate  the  splanchnic  nerves  just  where  they  pass 
through  the  pillars  of  the  diaphragm.  Stimulation  of  these  nerves  will 
cause  vaso-constriction  in  the  kidney,  which  takes  place  without  sharply 
affecting  the  blood  pressure. 

2.  Stimulate  the  depressor  nerve  or  the  central  end  of  the  divided  vagus. 
In  this  case  the  volume  of  the  kidney  will  increase  though  the  general  blood 
pressure  decreases,  showing  that  the  fall  of  blood  pressure  is  due  to  periph- 
eral vascular  dilatation. 

3.  Stimulate  the  peripheral  end  of  the  divided  vagus  so  as  to  slow  or 
even  completely  stop  the  heart.  The  sharp  fall  in  blood  pressure  is 
now  accompanied  by  decrease  in  the  volume  of  the  kidney,  showing  that  the 
kidney  change  is  merely  passively  following  that  of  the  blood  pressure. 


CHAPTER  VI 

RESPIRATION 

The  maintenance  of  animal  life  necessitates  the  continual  absorption  of 
oxygen  and  the  excretion  of  carbon  dioxide  by  the  living  tissues.  The  blood 
is  the  medium,  in  all  animals  which  possess  a  well-developed  blood-vascular 
system,  by  which  these  gases  are  carried.  Oxygen  is  absorbed  by  the  blood 
from  without  and  conveyed  to  all  parts  of  the  organism;  and  carbon  dioxide 
which  comes  from  the  cells  within  is  carried  by  the  blood  to  the  surfaces, 
from  which  it  may  escape  from  the  body.  The  two  processes — absorption 
of  oxygen  and  excretion  of  carbon  dioxide— are  complementary,  and  their 
sum  is  termed  the  process  of  Respiration. 

In  all  Vertebrata,  and  in  a  large  number  of  Invertebrata,  certain  parts, 
either  lungs  or  gills,  are  specially  constructed  for  bringing  the  blood  into 
proximity  with  the  aerating  medium  (atmospheric  air,  or  water  containing 
air  in  solution).  In  some  of  the  lower  Vertebrata  (frogs  and  other  naked 
Amphibia)  the  skin  is  important  as  a  respiratory  organ,  and  is  capable  of 
supplementing  to  some  extent  the  functions  of  the  proper  breathing  ap- 
paratus. 

A  lung  or  a  gill  is  constructed  essentially  of  a  fine  transparent  membrane, 
one  surface  of  which  is  exposed  to  the  air  or  water,  as  the  case  may  be,  while 
on  the  other  surface  is  a  network  of  blood-vessels.  The  only  separation  be- 
tween the  blood  and  aerating  medium  is  the  thin  wall  of  the  blood-vessels 
and  the  fine  membrane  on  which  the  vessels  are  distributed.  The  difference 
between  the  simplest  and  the  most  complicated  respiratory  membrane  is 
one  of  degree  only. 

In  the  mammals  and  the  higher  vertebrates  the  respiratory  membrane 
is  included  within  a  respiratory  cavity,  the  chest  or  thorax,  which  carries  on 
regular  movements,  the  respiratory  movements,  to  bring  changes  of  air  into 
close  contact  with  the  respiratory  surface. 

The  complexity  of  the  respiratory  membrane,  the  kind  of  aerating  medium, 
and  the  respiratoiy  movements  are  not,  however,  the  only  conditions  which 
cause  a  difference  in  the  respiratory  capacity  of  different  animals.  The 
quantity  and  composition  of  the  blood,  especially  as  regards  the  number 
and  size  of  the  red  corpuscles,  and  the  vigor  and  efficiency  of  the  circulatory 
apparatus  in  driving  the  blood  to  and  fro  between  the  lungs  and  the  active 
tissues,  these  are  conditions  of  equal,  if  not  greater,  importance. 

It  may  be  as  well  to  state  here  that  the  lungs  are  only  the  medium  for  the 

243 


INSPIRATION 


exchange,  on  the  part  of  the  blood,  of  carbon  dioxide  for  oxygen.  The 
living  tissues  are  the  seat  of  those  combustion  processes  which  consume 
oxygen  and  produce  carbon  dioxide.  These  processes  occur  in  all  parts  of 
the  body  in  the  substance  of  the  living  active  tissues,  and  are  the  true  respira- 
tory processes,  sometimes  called  internal  or  tissue  respiration. 

THE    RESPIRATORY    APPARATUS. 

The  object  of  the  respiratory  movements  being  the  interchange  of  gases 
in  the  lungs,  it  is  necessary  that  the  atmospheric  air  shall  pass  into  them 
and  that  the  changed  air  shall  be  expelled  from  them.  The  lungs  are  con- 
tained in  the  chest  or  thorax,  which  is  a  closed  cavity  having  no  communica- 


Fig.  218. — Outline  Showing  the  General  Form  of  the  Larynx,  Trachea,  and  Bronchi,  as  seen 
from  Before,  h,  The  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  t,  superior,  and  t',  inferior  cornu 
of  the  thyroid  cartilage;  c,  middle  of  the  cricoid  cartilage;  tr,  the  trachea,  showing  sixteen  cartilag- 
inous rings;   b,  the  right,  and  b' ,  the  left  bronchus.      X  J.      (Allen  Thomson.) 


THE     LARYNX  245 

tion  with  the  outside  except  by  means  of  the  respiratory  passages.  The  air 
enters  these  passages  through  the  nostrils  or  through  the  mouth,  thence  it 
passes  through  the  larynx  into  the  trachea  or  windpipe,  which  about  the 
middle  of  the  chest  divides  into  two  tubes,  the  bronchi,  one  to  each  lung. 

The  Larynx.  The  upper  part  of  the  passage  which  leads  exclu- 
sively to  the  lung  is  formed  by  the  thyroid,  cricoid,  and  arytenoid  carti- 
lages, figure  218,  and  contains  the  vocal  cords,  by  the  vibration  of  which  the 
voice  is  chiefly  produced.  These  vocal  cords  are  ligamentous  bands  covered 
with  mucous  membrane  and  attached  to  certain  cartilages  which  are  capable 
of  movement  by  muscles.  By  their  approximation  the  cords  can  entirely 
close  the  entrance  into  the  larynx;  but  under  ordinary  conditions  the  entrance 
of  the  larynx  is  formed  by  a  more  or  less  triangular  opening  between  them, 
called  the  rima  glotlidis.  Projecting  at  an  acute  angle  between  the  base  of 
the  tongue  and  the  larynx,  to  which  it  is  attached,  is  a  leaf-shaped  cartilage 
with  its  larger  extremity  free.  This  is  called  the  epiglottis.  The  whole  of 
the  larynx  is  lined  by  mucous  membrane,  which,  however,  is  extremely  thin 
over  the  vocal  cords.     At  its  lower  extremity  the  larynx  joins  the  trachea. 

Taste  buds  have  been  found  in  the  epithelium  of  the  posterior  surface  of 
the  epiglottis,  and  in  several  other  situations  in  the  laryngeal  mucous  mem- 
brane. 

The  Trachea  and  Bronchi.  The  trachea  extends  from  the  cricoid 
cartilage,  which  is  on  a  level  with  the  fifth  cervical  vertebra,  to  a  point  oppo- 
site the  third  dorsal  vertebra,  where  it  divides  into  the  two  bronchi,  one  for 
each  lung,  figure  218.  The  trachea  measures,  on  an  average,  four  or  four 
and  a  half  inches,  12  to  14  cm.,  in  length,  and  from  three-quarters  of  an  inch 
to  an  inch,  2  to  2.5  cm.,  in  diameter,  and  is  essentially  a  tube  of  fibro-elastic 
membrane  within  the  layers  of  which  are  enclosed  a  series  of  cartilaginous 
rings,  from  sixteen  to  twenty  in  number.  These  rings  extend  only  around 
the  front  and  sides  of  the  trachea,  about  two-thirds  of  its  circumference,  and 
are  deficient  behind;  the  interval  between  their  posterior  extremities  being 
bridged  over  by  a  continuation  of  the  fibrous  membrane  in  which  they  are 
enclosed,  figure  219,  //. 

Immediately  within  this  tube  and  at  the  back  is  a  layer  of  unstriped 
muscular  fibers.  This  muscular  layer  extends  transversely  between  the 
ends  of  the  cartilaginous  rings  to  which  it  is  attached,  and  also  opposite  the 
intervals  between  them;  its  evident  function  being  to  diminish  the  caliber 
of  the  trachea  by  approximating  the  ends  of  the  cartilages.  Outside  there 
are  a  few  longitudinal  bundles  of  muscular  tissue,  which,  like  the  preceding, 
are  attached  both  to  the  fibrous  and  to  the  cartilaginous  framework. 

The  mucous  membrane,  figures  219  and  220,  consists  largely  of  adenoid 
tissue,  separated  from  the  stratified  columnar  epithelium,  which  lines  it,  by  a 
homogeneous  basement  membrane.  This  is  penetrated  here  and  there  by 
channels  which  connect  the  adenoid  tissue  of  the  mucosa  with  the  inter- 


246 


RESPIRATION 


cellular  substance  of  the  epithelium.  The  stratified  columnar  epithelium 
is  formed  of  several  layers,  of  which  the  most  superficial  layer  is  ciliated  and 
the  cells  often  branched  downward.  Many  of  the  superficial  cells  are  of  the 
goblet  variety.  In  the  deeper  part  of  the  mucosa  are  many  elastic  fibers 
between  which  lie  connective-tissue  corpuscles  and  capillary  blood-vessels. 

Numerous  mucous  glands  are  situated  on  the  exterior  and  in  the  substance 
of  the  fibrous  framework  of  the  trachea;   their  ducts  perforating  the  various 


Fig.  2ig. — Section  of  the  Trachea,  a.  Columnar  ciliated  epithelium;  b  and  c,  proper  structure 
of  the  mucous  membrane,  containing  elastic  fibers  cut  across  transversely;  d,  submucous  tissue 
containing  mucous  glands,  e,  separated  from  the  hyaline  cartilage,  g,  by  a  fine  fibrous  tissue,  /, 
h,  external  investment  of  fine  fibrous  tissue.      (S.  K.  Alcock.) 


structures  which  form  the  wall  of  the  trachea,  and  opening  through  the 
mucous  membrane  into  the  cavity  of  the  trachea. 

The  two  bronchi  into  which  the  trachea  divides  resemble  the  trachea 
in  structure,  with  the  difference  that  in  them  there  is  a  distinct  layer  of  un- 
striped  muscle  arranged  circularly  beneath  the  mucous  membrane,  forming 
the  muscularis  mucosa.  On  entering  the  substance  of  the  lungs  the  carti- 
laginous rings,  although  they  still  form  only  larger  or  smaller  segments  of 


THE    TRACHEA     AND     BECNCHI 


247 


a  circle,  are  no  longer  confined  to  the  front  and  sides  of  the  tubes,  but  are 
distributed  impartially  to  all  parts  of  their  circumference. 

The   bronchi  divide    and    subdivide    in    the  substance  of   the  lungs  into 
smaller  and  smaller  branches,  which  penetrate  into  every  part  of  the  organ 


Fig.  220. — Ciliary  Epithelium  of  the  Human  Trachea,  a.  Layer  of  longitudinally  arranged 
elastic  fibers;  b,  basement  membrane;  c,  deepest  cells,  circular  in  form;  d,  intermediate  elongated 
cells;   e,  outermost  layer  of  cells  fully  developed  and  bearing  cilia.      X  350.      (Kolliker.) 

until  at  length  they  end   in    the  smaller    subdivisions  of    the  lungs  called 
lobules. 

All  the  larger  branches  have  walls  formed  of  tough  membrane,  contain- 
ing portions  of  cartilaginous  rings,  by  which  they  are  held  open,  and  un- 
striped  muscular  fibers,  as  well  as  longitudinal  bundles  of  elastic  tissue. 


Fig.  221. — Transverse  Section  of  a  Bronchus,  about  £  inch  in  Diameter,  e.  Epithelium 
(ciliated);  immediately  beneath  it  is  the  mucous  membrane  or  internal  fibrous  layer,  of  varying 
thickness;  m,  muscular  layer;  5.  m.  submucous  tissue;  f,  fibrous  tissue;  c,  cartilage  enclosed  within 
the  layers  of  fibrous  tissue;   g,  mucous  gland.      (F.  E.  Schulze.) 


They  are  lined  by  mucous  membrane,  the  surface  of  which,  like  that  of  the 
larynx  and  trachea,  is  covered  with  ciliated  epithelium;  but  the  several 
layers  become  less  and  less  distinct  until  the  lining  consists  of  a  single  layer 
of  more  or  less  .cubical  cells  covered  with  cilia,  figure  221.  The  mucous 
membrane  is  abundantly  provided  with  mucous  glands. 


248 


RESPIRATION 


As  the  bronchi  become  smaller  and  smaller  and  their  walls  thinner,  the 
cartilaginous  rings  become  fewer  and  more  irregular,  until  in  the  smaller 
bronchial  tubes  they  are  represented  only  by  minute  and  scattered  cartilag- 
inous flakes.  And  when  the  bronchi  by  successive  branches  are  reduced 
to  about  -fa  of  an  inch,  c.6  mm.,  in  diameter,  they  lose  their  cartilaginous  ele- 
ment altogether  and  their  walls  are  formed  only  of  a  tough,  fibrous,  elastic 
membrane  with  circular  muscular  fibers.  They  are  still  lined,  however, 
by  a  thin  mucous  membrane  with  ciliated  epithelium,  the  length  of  the  cells 
bearing  the  cilia  having  become  so  far  diminished  that  the  cells  are  almost 
cubical.  In  the  smaller  bronchi  the  circular  muscular  fibers  are  relatively 
more  abundant  than  in  the  larger  bronchi  and  form  a  distinct  circular  coat. 

The  Lungs  and  Plurae.  The  lungs  occupy  the  greater  portion 
of  the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on  section  appear 
to  the  naked  eye  as  if  they  were  in  great  part  solid  organs,  except  where 
branches  of  the  open  bronchi  or  air-tubes  may  have  been  cut  across  and  show 
on  the  surface  of  the  section.     In  fact,  however,  the  lungs  are  hollow  organs 


Fig.  222. — Transverse  Section  of  the  Chest. 

composed  of  a  mass  of  air  cavities  all  of  which  communicate  finally  with 
the  common  air-tube,  the  trachea. 

Each  lung  is  enveloped  by  a  serous  membrane,  the  pleura,  which  ad- 
heres closely  to  its  surface  and  provides  it  with  its  smooth  and  slippery 
covering.  This  same  membrane  lines  the  inner  surface  of  the  chest  wall. 
The  continuity  of  this  membrane,  which  forms  a  closed  sac  as  in  the  case 
of  other  serous  membranes,  will  be  best  understood  by  reference  to  figure  222. 
The  appearance  of  a  space,  however,  between  the  pleura  which  covers  the 
lung,  visceral  layer,  and  that  which  lines  the  inner  surface  of  the  chest,  parietal 
layer,  is  inserted  in  the  drawing  only  for  the  sake  of  distinctness.  These 
layers  are,  in  health,  everywhere  in  contact,  one  with  the  other;  and  between 
them  is  only  just  as  much  fluid  as  will  insure  frictionless  movement  in  their 
expansion  and  contraction. 


THE     FINER     STRUCTURE     OE     THE     LUNG 


249 


When  considering  the  subject  of  normal  respiration,  one  may  discard 
altogether  the  notion  of  the  existence  of  any  space  or  cavity  between  the 
lungs  and  the  wall  of  the  chest.  If,  however,  an  opening  be  made  so  as  to 
permit  air  or  fluid  to  enter  the  pleural  sac,  the  lung  in  virtue  of  its  elasticity 
recoils,  and  a  considerable  space  is  left  between  it  and  the  chest  wall.  In 
other  words,  the  natural  elasticity  of  the  lungs  would  cause  them  at  all  times 
to  contract  away  from  the  ribs  were  it  not  that  the  contraction  is  resisted  by 
atmospheric  pressure  which  bears  only  on  the  inner  surface  of  the  air-tubes 
and  air-cells. 

The  pulmonary  pleura  consists  of  an  outer  or  denser  layer  and  an  inner 
looser  tissue  in  which  there  is  a  lymph-canalicular  system.  Numerous  lym- 
phatics are  to  be  met  with,  which  form  a  dense  plexus  of  vessels,  many 
of  which  contain  valves.  They  are  simple  endothelial  tubes,  and  take  origin 
in  the  lymph-canalicular  system  of  the  pleura  proper.  Scattered  bundles 
of  unstriped  muscular  fiber  occur  in  the  pulmonary  pleura.  The}-  are  es- 
pecially strongly  developed  on  the  anterior  and  internal  surfaces  of  the  lungs, 
the  parts  which  move  most  freely  in  respiration.  Their  function  is  doubt- 
less to  aid  in  expiration. 

The  Finer  Structure  of  the  Lung.  Each  lung  is  partially  subdi- 
vided  into  separate   portions  called  lobes;    the  right   lung   into   three   lobes, 


Fig.  223. 

Fig.  223. — Terminal  Branch  of  a  Bronchial  Tube,  with  its  Infundibula  and  Air-cells,  from  the 
Margin  of  the  Lung  Injected  with  Quicksilver;  Monkey,  a,  Terminal  bronchial  twig;  b,  b,  in- 
fundibula and  air-cells.      X   10.      (F.  E.  Schulze.) 

Fig.  224. — Two  Small  Infundibula,  a,  a,  with  air-cells,  b,  b,  and  the  ultimate  bronchial  tubes, 
c,  c,  with  which  the  air-cells  communicate.      From  a  new-born  child.      (Kolliker.) 


and  the  left  into  two.  Each  of  these  lobes,  again,  is  composed  of  a  large  num- 
ber of  minute  parts,  called  lobules.  Each  pulmonary  lobule  may  be  considered 
to  be  a  lung  in  miniature,  consisting,  as  it  does,  of  a  branch  of  the  bronchial 
tube,  of  air-cells,  blood-vessels,  nerves,  and  lymphatics,  with  a  small  amount 
of  areolar  tissue. 


250 


RESPIRATION 


On  entering  a  lobule,  the  small  bronchial  tube,  the  structure  of  which 
has  just  been  described,  a,  figure  210,  divides  and  subdivides;  its  walls  at 
the  same  time  becoming  thinner  and  thinner,  until  at  length  they  are  formed 
only  of  a  thin  membrane  of  areolar  and  elastic  tissue,  lined  by  a  layer  of 
squamous  epithelium,  no  longer  provided  with  cilia.  At  the  same  time  they 
are  altered  in  shape;  each  of  the  minute  terminal  branches  widening  out 
funnel-wise,  and  its  walls  being  pouched  out  irregularly  into  small  saccular 
dilatations,  called  air-cells,  figure  223,  b.  Such  a  funnel-shaped  terminal 
branch  of  the  bronchial  tube,  with  its  group  of  pouches  or  air-cells,  has  been 
called  an  wjiindibitlum,  figures  223  and  224,  and  the  irregular  oblong  space 
in  its  center,  with  which  the  air-cells  communicate,  an  intercellular  passage. 


Fig.  225. — From  a  Section  of  the  Lung  of  a  Cat,  Stained  with  Silver  Nitrate.  A.  D,  Alveolar 
duct  or  intercellular  passage;  5,  alveolar  septa,  N,  alveoli  or  air-cells,  lined  with  large  flat, 
nuleated  cells,  with  some  smaller  polyhedral  nucleated  cells;  At,  unstriped  muscular  fibers.  Cir- 
cular muscular  fibers  are  seen  surrounding  the  interior  of  the  alveolar  duct,  and  at  one  part  is  seen 
a  group  of  small  polyhedral  cells  continued  from  the  bronchus.      (Klein  and  Noble  Smith  J 


An  inflated  and  dried  turtle's  lung  is  the  homologue  of  a  lobule.  Such  a 
preparation  can  be  cut  across  to  illustrate  the  intercellular  passage,  the  in- 
fundibulum,  and  the  air-cells. 

The  air-cells,  or  air-vessels,  are  sometimes  placed  singly,  like  recesses 
from  the  intercellular  passage,  but  more  often  they  are  arranged  in  groups 
or  even  rows,  like  minute  sacculated  tubes,  so  that  a  short  series  of  vesicles 
all  communicating  with  one  another  open  by  a  common  orifice  into  the  tube. 
The  vesicles  are  of  various  forms  according  to  the  mutual  pressure  to  which 


THE     FINER    STRUCTURE     OF    THE     LING 


251 


they  are  subject.  Their  walls  are  nearly  in  contact,  and  they  vary  from  0.5 
to  0.3  mm.  in  diameter.  Their  walls  are  formed  of  fine  membrane  similar 
to  that  of  the  intercellular  passages  and  continuous  with  it.  The  membrane 
is  folded  on  itself  so  as  to  form  a  sharp-edged  border  at  each  circular  orifice 
of  communication  between  contiguous  air-vesicles,  or  between  the  vesicles 
and  the  bronchial  passages.  Numerous  fibers  of  elastic  tissue  are  spread 
out  in  the  walls  between  contiguous  air-cells,  and  many  of  these  are  attached 
to  the  outer  surface  of  the  wall  of  which  each  cell  is  composed,  imparting  to 
it  additional  strength  and  the  power  of  recoil  after  distention. 

The  air-cells  are  lined  by  a  layer  of  epithelium,  figure  225,  the  cells  of 
which  are  very  thin  and  plate-like.  The  thin  epithelial  membrane  is  free  on 
one  side,  where  it  comes  in  contact  with  the  air  of  the  lungs,  but  on  the  other 


Fig.  226. — Section  of  Injected  Lung,  Including  Several  Contiguous  Alveoli.  (F.  E.  Schulze.) 
Highly  magnified,  a,  a.  Free  edges  of  alveoli;  c,  c,  partitions  between  neighboring  alveoli,  seen  in 
section;  b,  small  arterial  branch  giving  off  capillaries  to  the  alveoli.  The  looping  of  the  vessels  to 
either  side  of  the  partitions  is  well  exhibited.  Between  the  capillaries  is  seen  the  homogeneous 
alveolar  wall  with  nuclei  of  connective-tissue  corpuscles  and  elastic  fibers. 


side  a  network  of  pulmonary  capillaries  is  spread  out  so  densely,  figure  226, 
that  the  interspaces  or  meshes  are  even  narrower  than  the  vessels.  These 
are  on  an  average  -g-oVo  of  an  inch,  or  8  micromillimeters,  in  diameter.  Be- 
tween the  atmospheric  air-cells  and  the  blood  in  these  vessels,  nothing  in- 
tervenes but  the  thin  walls  of  the  cells  and  capillaries.  The  exposure  of  the 
blood  to  the  air  is  the  more  complete  because  the  wall  between  contiguous 
air-cells,  and  often  the  spaces  between  the  walls  of  the  same,  contain  only 
a  single  layer  of  capillaries  both  sides  of  which  are  at  once  exposed  to  the  air. 


252 


RESPIRATION 


The  air-vesicles  situated  nearest  to  the  center  of  the  lung  are  smaller 
and  their  networks  of  capillaries  are  closer  than  those  nearer  to  the  circum- 
ference. The  vesicles  of  adjacent  lobules  do  not  communicate.  Those  of 
the  same  lobule  or  proceeding  from  the  same  intercellular  passage  com- 
municate as  a  general  rule  only  near  angles  of  bifurcation,  so  that  when  any 
bronchial  tube  is  closed  or  obstructed  the  supply  of  air  is  lost  for  all  the  blood- 
vessels of  that  lobule  and  its  branches. 

Blood-supply.  The  lungs  receive  blood  from  two  sources:  a,  the 
pulmonary  artery;  b,  the  bronchial  arteries.  The  former  conveys  venous 
blood  to  the  lungs  for  its  oxidation,  and  this  blood  takes  no  share  in  the 
nutrition  of  the  deeper  pulmonary  tissues  through  which  it  passes.  The 
branches  of  the  bronchial  arteries  are  nutrient  arteries  which  ramify  in  the 


Fig.  227. — Capillary  Network  of  the  Pulmonary  Blood-vessels  in   the  Human  Lung. 

(Kolliker.) 


X  60. 


walls  of  the  bronchi,  in  the  walls  of  the  larger  pulmonary  vessels,  and  in  the 
interlobular  connective  tissue,  etc.  The  blood  of  the  bronchial  vessels  is  re- 
turned chiefly  through  the  bronchial,  but  partly  through  the  pulmonary,  veins. 

Lymphatics.  The  lymphatics  are  arranged  in  three  sets:  1.  Ir- 
regular lacuna;  in  the  walls  of  the  alveoli  or  air-cells.  The  lymphatic 
vessels  which  lead  from  these  accompany  the  pulmonary  vessels  toward 
the  root  of  the  lung.  2,  Irregular  anastomosing  spaces  in  the  walls  of  the 
bronchi.  3,  Lymph-spaces  in  the  pulmonary  pleura.  The  lymphatic  vessels 
from  all  these  irregular  sinuses  pass  in  toward  the  root  of  the  lung  to  reach 
the  bronchial  glands. 

Nerves.  The  nerves  of  the  lung  are  to  be  traced  from  the  anterior 
and  posterior  pulmonary  plexuses,  which  are  formed  by  branches  of  the 
vagus  and  sympathetic.  The  nerves  follow  the  course  of  the  blood-vessels 
and  bronchi,  and  many  small  ganglia  are  situated  in  the  walls  of  the  latter. 


INSPIRATION  253 

THE    MOVEMENTS    OF    THE    RESPIRATORY    MECHANISM. 

Respiratory  movement  consists  of  the  alternate  expansion  and  contrac- 
tion of  the  thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from 
the  lungs. 

A  movement  of  the  side  walls  or  floor  of  the  chest  to  increase  its  diameter 
or  length  will  enlarge  the  capacity  of  the  interior.  By  such  an  increase  of 
capacity  there  will  be  of  course  a  diminution  of  the  pressure  of  the  air  in  the 
lungs,  and  a  fresh  quantity  of  air  will  enter  through  the  larynx  and  trachea 
to  equalize  the  pressure  on  the  inside  and  outside  of  the  chest.  This  move- 
ment is  called  inspiration. 

The  movement  which  diminishes  the  capacity  of  the  chest  and  increases 
the  pressure  in  the  interior  expels  air  until  the  pressure  within  and  that  without 
the  chest  are  again  equal.  This  movement  is  called  expiration.  In  both 
cases  the  air  passes  through  the  trachea  and  larynx,  whether  in  entering  or 


Fig.  228. — Schematic  Representation  of  Diaphragm.     In  expiration  (/),  quiet  inspiration  (//), 
and  deep  inspiration  (///).      (After  Schaffer.) 

leaving  the  lungs,  there  being  no  other  communication  with  the  exterior  of 
the  body.  And  the  lung,  for  the  same  reason,  remains  closely  in  contact 
with  the  walls  and  floor  of  the  chest  under  all  the  circumstances  described. 
To  speak  of  expansion  of  the  chest  is  to  speak  also  of  expansion  of  the  lung, 
and  vice  versa. 

Inspiration.  The  enlargement  of  the  chest  during  inspiration  is 
due  to  muscular  action,  which  brings  about  an  increase  in  the  size  of  the 
chest  cavity  through  the  contraction  of  the  inspiratory  muscles,  the  role 
played  by  the  lungs  being  a  passive  one.  The  chest  cavity  is  increased  in 
its  three  axes,  the  vertical,  lateral,  and  antero-posterior  diameters.  The 
muscles  engaged  in  ordinary  inspiration  are:  the  diaphragm,  the  external  inter- 
costals,  and  the  scaleni  and  levatores  costarum.     During  forced  inspiration 


254 


RESPIRATION 


every  muscle  is  brought  into  play  which  by  its  contraction  tends  to  elevate 
the  ribs  and  sternum  or  which  will  fix  points  against  which  these  muscles 
can  act.     This  includes  almost  every  muscle  of  the  trunk  and  neck. 

Changes  in  the  vertical  diameter  are  due,  first,  to  the  contraction  of  the 
diaphragm.     This  muscle  lias  the  shape  of  a   ilattened  dome,  its  highest 


Esophagus 
Left  subclavian  artery 
Left  common  carotid  artery 
Left  superior  intercostal  vein 
Left  innominate  vein 


Parietal  pleura 
(cut  edge) 


Pericardium 


Parietal  pleura 
( cut  edge) 


Aortic  arch 

Pulmonary  artery 
Bronchus 

Pulmonary  veins 

Esophagus 


Diaphragm 


Fig.  229. — Thorax  from  the  Left,  Showing  Left  Pleural  Sac,  and  the  Diaphragm.     The  lung  is 

removed. 


point  being  the  central  tendon.  While  passive,  its  lower  portions  are  in 
apposition  with  the  chest  walls,  figure  228,  /.  On  contraction,  the  dome  is 
pulled  downward  and  the  lower  portion  is  pulled  away  from  the  chest  walls, 
the  downward  displacement  varying  from  6  to  12  mm.  in  normal  respira- 
tion, and  in  forced  respiration  may  amount  to  as  much  as  45  mm.  The 
tendency  of  the  diaphragm  to  pull  the  lower  ribs  and  lower  part  of  the  sternum 


INSPIRATION- 


'S 


{nward  is  counteracted  by  the  outward  pressure  of  the  abdominal  viscera, 
and  bv  the  action  of  the  quadrati  lumborum,  which  by  their  attachment  to 
the  last  ribs  fix  these  and,  in  case  of  deep  inspiration,  may  even  pull  them 
downward.  The  serrati  postiii  inferiores  also  aid,  being  attached  to  the 
four  lower  ribs. 

Changes  in  the  lateral  and  antero-posterior  diameters  are  effected  by  the 
raising  of  the  ribs,  which  are  attached  very  obliquely  to  the  spine  and  sternum. 
The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the  sides — the 
hinder  ends  being  prevented  from  performing  any  upward  movement  by 
their  pivot  attachment  to  the  spine.  The  movement  of  the  front  extremities 
of  the  ribs  is  of  necessity  limited  by  an  upward  and  forward  movement  of  the 


Fig.  230. — Diagram  of  Axes  of  Movement  of  Ribs. 


sternum  to  which  they  are  attached,  the  movement  being  greater  at  the  lower 
end  than  at  the  upper  end  of  the  sternum. 

The  axes  of  rotation  in  these  movements  are  two:  one  corresponding 
with  a  line  drawn  through  the  two  articulations  which  the  rib  forms  with 
the  spine,  a,  b,  figure  230,  and  the  other  with  a  line  drawn  from  one  of  these 
(head  of  rib)  to  the  sternum,  A  B,  figure  230;  the  motion  of  the  rib  around 
the  latter  axis  being  somewhat  after  the  fashion  of  raising  the  handle  of  a 
bucket.  The  elevation  of  the  ribs  is  accompanied  by  a  slight  opening  out  of 
the  angle  which  the  bony  part  forms  with  its  cartilage,  and  thus  an  additional 
means  is  provided  for  increasing  the  antero-posterior  diameter  of  the  chest. 
The  movements  of  all  the  ribs  except  the  twelfth  consist  of  a  rotation  up- 
ward, forward,  and  outward.  The  twelfth  presents  only  rotation  down- 
ward and  backward. 


25()  RESPIRATION 

The  muscles  involved  in  these  movements  of  the  ribs  are  the  external 
intercostals  and  the  part  of  the  internal  intercostals  situated  between  the 
costal  cartilages.  Their  action  is  to  widen  the  intercostal  spaces.  The 
scaleni  fix  the  first  and  second  ribs,  thereby  making  a  fixed  point  of  action 
for  the  other  muscles  involved.  The  serrati  postici  superiores  assist  the  above 
and  also  raise  the  third,  fourth,  and  fifth  ribs.  The  levatores  costarum  longi 
and  brevi  elevate  and  evert  all  the  ribs  from  the  first  to  the  tenth. 

In  extraordinary  or  forced  inspiration,  which  may  be  due  either  to  violent 
exercise  or  to  interference  with  the  due  entrance  of  air  into  the  lungs,  all  the 
above  muscles  act  more  strongly.  The  diaphragm  descends  lower,  the  scaleni 
raise  the  first  and  second  ribs  instead  of  merely  fixing  them,  as  in  ordinary 
respiration,  as  do  also  the  sterno-cleido-mastoids.  These,  together  with  the 
erector  spina?,  which  straighten  the  spine,  increase  the  vertical  diameter. 
The  trapezii  and  the  rhomboidii  assist  in  increasing  the  antero-posterior  and 
lateral  diameters  by  fixing  the  shoulders  and  thus  giving  a  fixed  point  for  the 
action  of  the  pectorals  and  latissimi  dorsi. 

The  enlargement  of  the  chest  during  inspiration  presents  peculiarities 
in  different  persons.  In  children  of  both  sexes  the  principal  muscle  in- 
volved seems  to  be  the  diaphragm,  and  this  type  of  breathing  is  known  as 
abdominal  breathing.  In  men,  the  chest  and  sternum,  together  with  the 
front  wall  of  the  abdomen,  are  subject  to  a  wide  movement;  this  type  of 
breathing  is  called  the  inferior  costal.  In  women,  the  movement  appears 
less  extensive  in  the  lower  and  more  extensive  in  the  upper  part  of  the  chest, 
which  is  called  the  superior  costal  type.  This  has  been  shown  to  be  due 
rather  to  mode  of  dress  than  to  a  real  difference  in  the  sexes  (Mosher). 

Expiration.  Quiet  expiration  is  a  passive  act  due  to  the  return 
of  the  thorax  and  its  contained  lungs  to  their  normal  position  when  the  mus- 
cles involved  in  inspiration  relax.  This  elastic  recoil  is  sufficient  in  ordinary 
quiet  breathing  to  expel  air  from  the  lungs.  In  forced  expiration,  however, 
which  may  occur  to  a  slight  degree  in  speaking,  singing,  etc.,  as  well  as  in 
the  case  of  many  involuntary  and  reflex  acts,  such  as  coughing,  sneezing, 
etc.,  other  muscles  are  involved.  Of  these  the  principal  are  the  abdominal 
muscles,  obliquus  extemus  and  intcrmts,  rectus  abdominis,  transversalis  ab- 
dominis and  pyramidalis.  These  act,  first,  by  pressing  the  abdominal 
viscera  against  the  diaphragm  and  thereby  forcing  it  up,  their  descent  into 
the  pelvic  cavity  being  prevented;  second,  by  their  attachments  to  the  lower 
ribs  and  cartilages,  they  draw  these  downward  and  inward,  thereby  lessening 
the  size  of  the  thoracic  cavity;  lastly,  by  their  contraction,  they  form  a  fixed 
point  for  the  action  of  that  part  of  the  internal  intercostals,  not  involved  in 
inspiration,  to  approximate  the  ribs. 

When  by  the  efforts  of  the  expiratory  muscles  the  chest  has  been  squeezed 
to  less  than  its  average  diameters,  it  again,  on  relaxation  of  the  muscles, 
returns  to  the  normal  dimensions  bv  virtue  of  its  elasticity.     The  construe- 


RECORDING     RESPIRATORY     MOVEMENTS 


257 


tion  of  the  chest  walls,  therefore,  admirably  adapts  them  for  recoiling  against 
and  resisting  as  well  undue  contraction  as  undue  dilatation. 

Respiratory  Movements  of  the  Nostrils  and  of  the  Glottis.  During 
the  action  of  the  inspiratory  muscles  which  directly  draw  air  into  the  chest, 
those  which  guard  the  opening  through  which  the  air  enters  are  also  active. 
In  hurried  breathing  the  dilatation  of  the  nostrils  is  well  seen,  although 
under  ordinary  conditions  it  may  not  be  noticeable.  The  opening  at  the 
upper  part  of  the  larynx,  however,  the  rima  glottidis,  is  dilated  at  each  in- 
spiration for  the  more  ready  passage  of  air,  and  becomes  smaller  at  each 
expiration;  its  condition,  therefore,  corresponds  during  respiration  with 
that  of  the  walls  of  the  chest.  There  is  a  further  likeness  between  the  two 
acts  in  that,  under  ordinary  circumstances,  the  dilatation  of  the  rima  glot- 
tidis is  a  muscular  act  and  its  contraction  chiefly  an  elastic  recoil;  although, 
under  various  special  conditions  to  be  hereafter  mentioned,  there  may  be 
considerable  muscular  contraction  exercised. 

Methods  of  Recording  Respiratory  Movements.  The  movements  of  respiration 
may  be  recorded  graphically  in  several  ways.  The  ordinary  method  is  to  introduce  a 
tube  into  the  trachea  of  an  animal,  and  to  connect  this  tube  by  some  gutta-percha  tubing 
with  a  T-piece,  the  side  branch  of  which  is  connected  with  a  Marey's  tambour,  which  may 
be  made  to  write  on  a  recording  surface,  figure  173.  If  the  tube  attached  to  the  free  limb 
of  the  T-piece  be  partially  closed  with  a  screw  compress,  the  movements  of  inspiration 


Fig.  231. — Stethognph  or  Pneumograph,  h.  Tambour  fixed  at  right  angles  to  plate  of  steel,  f\ 
c  and  d,  arms  by  which  i  strument  is  attached  to  chest  by  belt,  e.  When  the  chest  expands,  the 
arms  are  pulled  asu,  der,  which  bends  the  steel  plate,  and  the  tambour  is  affected  by  the  pressure  of 
b,  which  is  attached  to  it  on  the  one  hand,  and  to  the  upright  in  connection  with  horizontal  screw,  g. 
(Modified  from  Marey's  instrument.) 


and  expiration  are  larger  than  if  it  were  open.  The  alteration  of  the  pressure  within  the 
lungs  on  inspiration  and  expiration  is  shown  by  the  movement  of  the  column  of  air  in  the 
trachea  and  in  its  extension  to  the  T-piece.  By  these  means  a  record  of  the  respiratory 
movements  may  be  obtained. 

Various  instruments  have  been  devised  for  recording  the  movements  of  the  chest 
by  application  of  apparatus  to  the  exterior.     Such  is  the  stethometer  of  Burdon-Sanderson, 
figure  233.     This  consists  of  a  frame  formed  of  two  parallel  steel  bars  joined  by  a  third 
17 


258 


RESPIRATION 


at  one  end.  At  the  free  end  of  the  bars  is  attached  a  leather  strap,  by  means  of  which 
the  apparatus  may  be  suspended  from  the  neck.  Attached  to  the  inner  end  of  one  bar  is 
a  tambour  and  ivory  button,  to  the  end  of  the  other  an  ivory  button.  The  apparatus  is 
suspended  with  the  transverse  bar  posteriorly,  the  button  of  the  tambour  is  placed  on  the 
part  of  the  chest  the  movement  of  which  it  is  desired  to  record,  and  the  other  button  is 
made  to  press  upon  the  corresponding  side  of  the  chest,  so  that  the  chest  is  held  as  between 
a  pair  of  calipers.  The  receiving  tambour  is  connected  through  a  T-piece  with  a  recording 
tambour  of  Marcy's,  and  with  a  bulb  by  means  of  which  air  can  be  squeezed  into  the 
cavity  of  the  tympanum.  When  adjusted,  the  tube  connected  with  the  air  ball  is  shut  off 
by  means  of  a  screw  clamp.  The  movement  of  the  chest  is  thus  communicated  to  the 
recording  tambour. 

A  simpler  form  of  this  apparatus,  called  a  pneumograph  or  stethograph,  consists  of  a 
thick  India-rubber  bag  of  elliptical  shape  about  three  inches  long,  to  one  end  of  which  a 
rigid  gutta-percha  tube  is  attached.  This  bag  may  be  fixed  at  any  required  place  on  the 
chest  by  means  of  a  strap  and  buckle.  By  means  of  the  gutta-percha  tube  the  variations 
of  the  pressure  of  air  in  the  bag,  produced  by  the  movements  of  the  chest,  are  communicated 


Fig.  232. — Tracing  of  Thoracic  Respiratory  Movements  obtained  by  means  of  Marey's  Pneu- 
mograph. (Foster.)  A  whole  respiratory  phase  is  comprised  between  a  and  a;  inspiration  during 
which  the  lever  descends,  extending  from  o  to  b,  and  expiration  from  b  to  o.  The  undulations  at 
c  are  caused  by  the  heart's  beat. 


to  a  recording  tambour.  This  principle  is  applied  in  a  modified  form  in  Marey's  pneumo- 
graph, figure  231. 

The  variations  of  intrapleural  pressure  may  be  recorded  by  introducing  a  cannula  into 
the  pleural  or  pericardial  cavity.  The  cannula  should  be  previously  connected  with  a 
mercury  or  other  form  of  manometer  by  tubing  filled  with  physiological  saline. 

Finally,  it  has  been  found  possible  in  various  ways  to  record  the  diaphragmatic  move- 
ments. This  can  be  done  by  inserting  a  receiving  tambour  into  the  abdomen  below  the 
diaphragm,  by  the  insertion  of  needles  into  different  parts  of  the  diaphragm  and  recording 
the  movement  of  the  free  ends  of  needles  about  the  fulcrum  formed  where  the  chest  wall 
is  pierced,  or  by  recording  the  contraction  of  isolated  strips  of  the  diaphragm  directly. 
These  records  all  give  an  accurate  picture  of  the  movements  of  the  diaphragm. 

The  Relative  Time  of  Inspiration  and  Expiration  and  the  Respira- 
tory Movement.  The  acts  of  inspiration  and  expiration  take  up,  un- 
der ordinary  circumstances,  a  nearly  equal  time.  The  time  of  inspiration, 
however,  especially  in  women  and  children,  is  a  little  shorter  than  that  of 
expiration,  and  there  is  commonly  a  very  slight  pause  between  the  end  of 
expiration  and  the  beginning  of  the  next  inspiration,  see  figure  232.  The 
ratio  of  the  respiratory  rhythm  may  be  thus  expressed: 

Inspiration 6 

Expiration 7  to  8 

Pause Very  slight 


QUANTITY     OF    AIR     BREATHED 


259 


If  the  ear  be  placed  in  contact  with  the  wall  of  the  chest,  or  be  separated 
from  it  only  by  a  good  conductor  of  sound  or  a  stethoscope,  a  faint  respiratory 
murmur  is  heard  during  inspiration.  This  sound  varies  somewhat  in  different 
parts,  being  loudest  or  coarsest  in  the  neighborhood  of  the  trachea  and  large 
bronchi  (tracheal  and  bronchial  breathing),  and  fading  off  into  a  faint  sighing 
as  the  ear  is  placed  at  a  distance  from  these  (vesicular  breathing).  It  is 
heard  best  in  children.  In  them  a  faint  murmur  is  heard  in  expiration  also. 
The  cause  of  the  vesicular  murmur  has  received  various  explanations.     Most 


Tambour. 
Ivory  button. 


Tube  to  commu- 
nicate with  re- 
cording tam- 
bour, 


Ball  to  fill  appa-  _ 
ratua  with  air 


Fig.  233. — Stethometer.      (Burdon-Sanderson.) 


observers  hold  that  the  sound  is  produced  in  the  glottis  and  larger  bronchial 
tubes,  but  that  it  is  modified  in  its  passage  to  the  pulmonary  alveoli.  In 
disease  of  the  lungs  the  vesicular  murmur  undergoes  various  modifica- 
tions, for  a  description  of  which  one  must  consult  text-books  on  physical 
diagnosis. 

The  Quantity  of  Air  Breathed.  Tidal  air  is  the  quantity  of  air 
which  is  habitually  and  almost  uniformly  changed  in  each  act  of  breathing. 
In  a  healthy  adult  man  it  is  about  30  cubic  inches,  or  about  500  c.c.  or  half 
a  liter.  In  college  students  the  tidal  air  is  somewhat  less,  varying  from  300 
to  400  c.c. 

The  Complemental  Air  is  the  quantity  of  air  which  can  be  drawn  into  the 
lungs  by  the  deepest  inspiration  over  and  above  that  which  is  in  the  lungs 


260 


RESPIRATION 


at  the  end  of  an  ordinary  inspiration.  Its  amount  varies,  but  may  be  reck- 
oned as  ioo  cubic  inches,  or  about  1,600  c.c. 

The  Reserve  Air  is  that  which  may  be  expelled  by  a  forcible  and  deeper 
expiration,  after  an  ordinary  expiration,  such  as  that  which  expels  the  tidal 
air.  The  reserve  air  amounts  to  from  1,200  to  1,500  c.c.  This  is  also  termed 
the  supplemental  air. 

The  Residual  Air  is  the  quantity  which  still  remains  in  the  lungs  after 
the  most  violent  expiratory  effort.     Its  amount  depends  in  great  measure 


'  II  1  I  II  I  I  i  II  1 1  I  I  1  1 1  I  1 1 1  1 1  II  I  I  I  I  I  I  I  I  I 

Fig.  234. — Tracing  of  the  Normal  Diaphragm  Respirations  of  the  Rabbit,  a.  With  quick 
movement  of  drum;  b,  with  slow  movement;  J,  inpiration;  E,  expiration.  To  be  read  from  left 
to  right.      (Marckwald.) 


on  the  absolute  size  of  the  chest,  but  may  be  estimated  at  about  1,000  c.c. 
to  1,200  c.c. 

The  total  quantity  of  air  which  passes  into  and  out  of  the  lungs  of  an 
adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inches.  This  quantity, 
however,  is  largely  increased  by  exertion;  the  average  amount  for  a  hard- 
working laborer  in  the  same  time  being  1,568,390  cubic  inches. 

The  Respiratory  Capacity.  The  greatest  respiratory  capacity  or  vital 
capacity  of  the  chest  is  indicated  by  the  quantity  of  air  which  a  person  can 
expel  from  his  lungs  by  a  forcible  expiration  after  the  deepest  possible  in- 
spiration. The  vital  capacity  is  the  sum  of  the  reserve,  tidal,  and  comple- 
mental  airs.  It  expresses  the  power  which  a  person  has  of  breathing  in  the 
emergencies  of  active  exercise,  violence,  and  disease.  The  average  capacity 
of  an  adult,  at  15. 40  C.  (6o°  F.),  is  about  225  to  250  cubic  inches,  or  3,500 
to  4,000  c.c. 


THE    RESPIRATORY     CAPACITY 


261 


The  respiratory  capacity,  or  as  John  Hutchinson  called  it,  vital  capacity,  is  usually 
measured  by  a  modified  gasometer  or  spirometer,  into  which  the  experimenter  breathes, 
making  the  most  prolonged  expiration  possible  after  the  deepest  possible  inspiration. 
The  quantity  of  air  which  is  thus  expelled  from  the  lungs  is  indicated  by  the  height  to 
which  the  air  chamber  of  the  spirometer  rises;  and  by  means  of  a  scale  placed  in  con- 
nection with  this,  the  number  of  cubic  inches  or  centimeters  is  read  off. 

In  healthy  men,  the  respiratory  capacity  varies  chiefly  with  the  stature, 
weight,  and  age. 

Circumstances  Affecting  the  Amount  of  Respiratory  Capacity.  For  every  inch  of 
height  above  the  standard  the  respiratory  capacity  is  increased,  on  an  average,  by  eight 
inches;   and  for  every  inch  below,  it  is  diminished  by  the  same  amount. 

The  influence  of  weight  on  the  capacity  of  respiration  is  less  manifest,  and  consider- 
ably less  than  that  of  height.     It  is  difficult  to  arrive  at  any  definite  conclusions  on  this 


Fig.  235. — Diagram  of  Hutchinson's  Spirometer.  (Landois.)  A ,  Graduated  cylinder  serving 
as  a  receiver  for  the  breath;  it  is  supplied  with  a  stopcock  at  the  top  for  the  ready  expulsion  of  air, 
and  is  balanced  by  weights  passing  over  pulleys.  B,  Mouthpiece  with  tube  reaching  nearly  to  the 
top  of  the  graduated  receiver  (.4)  when  the  latter  is  sunk  in  the  reservoir  ready  for  an  experiment; 
there  is  a  stopcock  in  this  tube  near  the  first  angle,  to  prevent  regurgitation  of  air.  C,  Reservoir 
for  the  graduated  receiver.  In  using  the  spirometer  the  reservoir  and  graduated  receiver  are  filled 
with  water,  or,  to  prevent  the  absorption  of  carbon  dioxide,  with  a  saturated  aqueous  solution  of 
common  salt  (NaCJ).  When  ready  for  an  experiment,  the  stopcock  at  the  top  of  the  receiver 
is  closed  and  that  in  the  tube  of  the  mouthpiece  opened,  and  the  breath  forced  into  the  receiver. 
The  receiver  rises  as  fast  as  the  breath  displaces  the  water.  After  the  breath  is  forced  into  the  re- 
ceiver the  stopcock  in  the  tube  of  the  mouthpiece  is  closed,  and  the  water  outside  and  inside  the 
receiver  brought  to  the  same  level,  so  that  the  air  within  the  receiver  shall  be  at  the  atmospheric 
pressure.  The  amount  of  breath  within  the  receiver  is  then  read  directly  from  the  scale  attached 
to  the  receiver.  For  accurate  measurement  the  breath  should  stand  a  few  minutes  to  acquire  the 
temperature  of  the  liquid  over  which  it  is  collected  ;  then  the  various  corrections  for  aqueous  vapor 
tension,  and  the  variations  from  the  standard  temperature  and  pressure,  should  be  made. 

point,  because  the  natural  average  weight  of  a  healthy  man  in  relation  to  stature  has  not 
yet  been  determined. 

By  age,  the  capacity  appears  to  be  increased  from  about  the  fifteenth  to  the  thirty- 
fifth  year,  at  the  rate  of  five  cubic  inches  per  year;  from  thirty-five  to  sixty-five  it  di- 
minishes at  the  rate  of  about  one  and  a  half  cubic  inches  per  year;  so  that  the  capacity  of 
respiration  of  a  man  sixty  years  old  would  be  about  thirty  cubic  inches  less  than  that 
of  a  man  forty  years  old,  of  the  same  height  and  weight.     (John  Hutchinson.) 


262  RESPIRATION 

The  number  of  respirations  in  a  healthy  adult  person  usually  ranges 
from  14  to  18  per  minute.  It  is  greater  in  infancy  and  childhood.  It  varies 
also  much  according  to  different  circumstances,  such  as  exercise  or  rest, 
health  or  disease,  etc.  Variations  in  the  number  of  respirations  correspond 
ordinarily  with  similar  variations  in  the  pulsations  of  the  heart.  In  health 
the  proportion  is  about  1  to  4,  or  1  to  5;  and  when  the  rapidity  of  the  heart's 
action  is  increased,  that  of  the  chest  movement  is  commonly  increased  also, 
but  not  in  every  case  in  equal  proportion.  It  happens  occasionally  in  disease, 
especially  of  the  lungs  or  air-passages,  that  the  number  of  respiratory  acts 
increases  in  quicker  proportion  than  the  beats  of  the  pulse;  and,  in  other 
affections,  much  more  commonly,  that  the  number  of  the  pulses  is  greater 
in  proportion  than  that  of  the  respirations. 

The  Force  of  Inspiratory  and  Expiratory  Muscles.  The  force 
which  the  inspiratory  muscles  are  capable  of  exerting  on  the  chest  is  greatest 
in  individuals  of  the  height  of  from  five  feet  seven  inches  to  five  feet  eight 
inches,  and  is  equal  to  a  column  of  three  inches  of  mercury.  Above  this 
height  the  force  decreases  as  the  stature  increases;  so  that  the  average 
power  of  men  of  six  feet  is  measured  by  about  two  and  a  half  inches  of  mer- 
cury. The  force  manifested  in  the  strongest  expiratory  acts  is,  on  the 
average,  one-third  greater  than  that  exercised  in  inspiration.  But  this 
difference  is  in  a  great  measure  due  to  the  power  exerted  by  the  elastic 
reaction  of  the  walls  of  the  chest;  and  it  is  also  much  influenced  by  the 
disproportionate  strength  which  the  expiratory  muscles  attain  from  their 
being  called  into  use  for  other  purposes  than  that  of  simple  expiration. 
The  force  of  the  inspiratory  act  is,  therefore,  better  adapted  than  that  of 
the  expiratory  for  testing  the  muscular  strength  of  the  body  (John 
Hutchinson). 

It  has  been  shown  that  within  the  limits  of  ordinary  tranquil  respiration 
the  elastic  resilience  of  the  walls  of  the  chest  favors  inspiration;  and  that  it 
is  only  in  deep  inspiration  that  the  ribs  and  rib-cartilages  offer  an  opposing 
force  to  their  dilatation.  In  other  words,  the  elastic  resilience  of  the  lungs, 
at  the  end  of  an  act  of  ordinary  exhalation  has  drawn  the  chest  walls  within 
the  limits  of  their  normal  degree  of  expansion.  Under  all  circumstances,  of 
course,  the  elastic  tissue  of  the  lungs  opposes  inspiration  and  favors  expiration. 

It  is  possible  that  the  contractile  power  which  the  bronchial  tubes  and 
air-vesicles  possess,  by  means  of  their  muscular  fibers  may  assist  in  expiration. 
But  it  is  more  likely  that  its  chief  purpose  is  to  regulate  and  adapt,  in  some 
measure,  the  quantity  of  air  admitted  to  the  lungs,  and  to  each  part  of  them, 
according  to  the  supply  of  blood.  The  muscular  tissue  contracts  upon  and 
gradually  expels  collections  of  mucus,  which  may  have  accumulated  within 
the  tubes,  and  which  cannot  be  ejected  by  forced  expiratory  efforts,  owing 
to  collapse  or  other  morbid  conditions  of  the  portion  of  lung  connected  with 
the  obstructed  tubes  (Gairdner).     Apart  from  any  of  the  before-mentioned 


COMPOSITION     OF    THE    ATMOSPHERE  263 

functions,  the  presence  of  muscular  fiber  in  the  walls  of  a  hollow  viscus,  such 
as  a  lung,  is  only  what  might  be  expected  from  analogy  with  other  organs. 
Subject  as  the  lungs  are  to  such  great  variation  in  size,  it  might  be  antici- 
pated that  the  elastic  tissue,  which  enters  so  largely  into  their  composition, 
would  be  supplemented  by  the  presence  of  much  muscular  fiber. 

RESPIRATORY  CHANGES  IN  THE  AIR  BREATHED. 

Composition  of  the  Atmosphere.  The  atmosphere  we  breathe  has, 
in  every  situation  in  which  it  has  been  examined  in  its  natural  state,  a 
nearly  uniform  composition.  It  is  a  mixture  of  oxygen,  nitrogen,  carbon 
dioxide,  and  watery  vapor,  with,  commonly,  traces  of  other  gases,  as  argon, 
ammonia,  sulphureted  hydrogen,  etc.  Of  every  ioo  volumes  of  pure  at- 
mospheric air,  79  volumes,  on  an  average,  consist  of  nitrogen  and  argon, 
the  remaining  21  of  oxygen.  The  proportion  of  carbon  dioxide  is  extremely 
small;    10,000  volumes  of  atmospheric  air  contain  only  about  3  of  that  gas. 

The  quantity  of  watery  vapor  varies  greatly  according  to  the  tem- 
perature and  other  circumstances,  but  the  atmosphere  is  never  without 
some.  In  this  country  the  average  quantity  of  watery  vapor  in  the  atmos- 
phere varies  greatly  according  to  the  region.  In  some  of  our  Western  arid 
plains  in  the  dry  season  the  air  is  almost  free  of  moisture. 

Composition  of  Air  which  Has  Been  Breathed.  The  changes 
effected  by  respiration  in  the  atmospheric  air  are:  1,  an  increase  of  tem- 
perature; 2,  an  increase  in  the  quantity  of  carbon  dioxide;  3,  a  diminution 
in  the  quantity  of  oxygen;  4,  a  diminution  of  volume;  5,  an  increase  in  the 
amount  of  watery  vapor;  6,  the  addition  of  a  minute  amount  of  organic 
matter  and  of  free  ammonia. 

Temperature  0}  the  Expired  Air.  Expired  air,  after  its  contact  with  the 
interior  of  the  lungs,  is  hotter  (at  least  in  most  climates)  than  the  inspired  air. 
Its  temperature  varies  between  360  and  37.50  C.  (970  and  99. 50  F.),  the  lower 
temperature  being  observed  when  the  air  has  remained  but  a  short  time  in 
the  lungs.  Whatever  may  be  the  temperature  of  the  air  when  inhaled,  it 
acquires  nearly  that  of  the  blood  before  it  is  expelled  from  the  chest. 

The  Carbon  Dioxide  of  Expired  Air.  The  percentage  of  carbon  dioxide 
is  increased,  but  the  quantity  exhaled  in  a  given  time  is  subject  to  change 
from  various  circumstances.  From  every  volume  of  air  inspired  4  to  5  per 
cent  of  oxygen  is  abstracted;  while  a  rather  smaller  quantity,  4.38  per  cent, 
of  carbon  dioxide  is  added  in  its  place;  the  expired  air  will  contain,  there- 
fore, 438  volumes  of  carbon  dioxide  in  10,000.  The  total  quantity  of  carbon 
dioxide  exhaled  into  the  air  breathed  by  a  healthy  adult,  calculating  that 
15.4  c.c.  of  the  350C.C.  of  the  average  air  breathed  out  at  each  expiration  con- 
sists of  carbon  dioxide,  and  that  the  rate  of  respiration  is  on  an  average  16, 
would  be  about  400  liters  in  the  twenty-four  hours.    From  actual  experiment  this 


204 


RESPIRATION 


amount  seems  to  be  a  trifle  too  great,  since  from  the  average  of  many  inves- 
tigations the  total  amount  of  carbon  dioxide  excreted  per  day  by  the  entire 
body  has  been  found  to  be  about  400  liters,  weighing  800  grams,  and  con- 
sisting of  218  grams  of  carbon,  and  582  grams  of  oxygen.  From  the  218 
grams  of  carbon  must  be  deducted  about  10  grams  excreted  in  other  ways 


Fig.  236. — Apparatus  for  Estimating  02  and  C02  in  Expired  Air.     (Waller.) 

than  by  the  lungs,  which  leaves  about  215  grams  as  the  amount  of  carbon  ex- 
creted by  the  average  healthy  man  by  respiration  each  day  and  night.  These 
quantities  must  be  considered  approximate  only,  inasmuch  as  various  cir- 
cumstances, even  in  health,  influence  the  amount  of  carbon  dioxide  excreted, 
and,  correlatively,  the  amount  of  oxygen  absorbed. 

Circumstances  Influencing  the  Amount  of  Carbon  Dioxide  Excreted.  Age  and  Sex. 
The  quantity  of  carbon  dioxide  exhaled  into  the  air  breathed  by  males,  regularly  in- 
creases from  8  to  30  years  of  age;  from  30  to  50  the  quantity,  after  remaining  stationary  for 
a  while,  gradually  diminishes,  and  from  50  to  extreme  age  it  goes  on  diminishing,  till  it 
scarcely  exceeds  the  quantity  exhaled  at  10  years  old.  In  females  (in  whom  the  quantity 
exhaled  is  always  less  than  in  males  of  the  same  age)  the  same  regular  increase  in  quantity 
goes  on  from  the  8th  year  to  the  age  of  puberty,  when  the  quantity  abruptly  ceases  to  in- 
crease, and  remains  stationary  so  long  as  they  continue  to  menstruate.  When  menstrua- 
tion has  ceased,  the  carbon  dioxide  output  soon  decreases  at  the  same  rate  as  it  does  in 
old  men. 


AMOUNT     OF    CARBON    DIOXIDE     EXCRETED  265 

Respiratory  Movements.  The  quicker  the  respirations,  the  smaller  is  the  percentage 
of  carbon  dioxide  contained  in  each  volume  of  the  expired  air.  Although  the  propor- 
tionate quantity  of  carbon  dioxide  is  thus  diminished,  tne  absolute  amount  exhaled 
within  a  given  time  is  increased  thereby,  owing  to  the  larger  quantity  of  air  which  is 
breathed  in  the  time.  The  last  half  of  a  volume  of  expired  air  contains  more  carbonic 
acid  than  the  half  first  expired;  a  circumstance  which  is  explained  by  the  later  portion 
of  air  coming  from  the  remote  part  of  the  lungs,  where  it  has  been  in  more  immediate 
and  prolonged  contact  with  the  blood  than  the  first  portion  exhaled  has,  which  comes 
chiefly  from  the  larger  bronchial  tubes. 

External  Temperature.  The  observation  made  by  Vierordt  at  various  temperatures 
between  3-40-23.8°  C.  (380  F.  and  750  F.)  show,  for  warm-blooded  animals,  that  within 
this  range  every  rise  equal  to  5.50  C.  (io°  F.)  causes  a  diminution  of  about  ^^  c.c.  (2 
cubic  inches)  in  the  quantity  of  carbon  dioxide  exhaled  per  minute. 

Season  of  the  Year.  The  season  of  the  year,  independently  of  temperature,  materi- 
ally influences  the  respiratory  phenomena  since  it  influences  the  metabolism  of  the  body; 
spring  being  the  season  of  the  greatest,  and  autumn  of  the  least,  activity  of  the  respira- 
tory and  metabolic  functions. 

Purity  of  the  Respired  Air.  The  average  quantity  of  carbon  dioxide  given  out  by  the 
lungs  constitutes  about  4.38  per  cent  of  the  expired  air;  but  if  the  air  which  is  breathed 
be  previously  impregnated  with  carbon  dioxide  (as  is  the  case  when  the  same  air  is  fre- 
quently respired),  then  the  quantity  of  carbon  dioxide  exhaled  becomes  relatively  much 
greater. 

Hygrometric  State  of  the  Atmosphere.  The  amount  of  carbon  dioxide  exhaled  is  con- 
siderably influenced  by  the  degree  of  moisture  of  the  atmosphere,  much  more  being  given 
off  when  the  air  is  moist  than  when  it  is  dry. 

Period  of  the  Day.  The  respiratory  quotient,  i.e.,  the  ratio  between  carbon  dioxide 
eliminated  and  oxygen  absorbed,  is  greater  during  the  day  than  during  the  night.  In 
the  day,  therefore,  the  CO2  exhaled  in  relation  to  the  O2  absorbed  is  increased,  and  it 
is  diminished  during  the  night.  This  is  probably  due  to  the  increased  production  of 
CO2  as  a  result  of  increased  tissue  activity  during  the  day,  and,  consequently,  the 
breaking  down  or  catabolism  of  more  substances. 

Food  and  Drink.  By  the  use  of  food  the  quantity  of  CO,  is  increased,  while  by  fast 
ing  it  is  diminished;  it  is  greater  when  animals  are  fed  on  farinaceous  food  than  when 
fed  on  meat.  The  effects  produced  by  spirituous  drinks  depend  much  on  the  kind  of 
drink  taken.  Pure  alcohol  in  very  small  amounts  tends  rather  to  increase  than  to  lessen 
respiratory  changes,  and  the  amount,  therefore,  of  carbon  dioxide  expired.  Rum,  ale,  and 
porter,  also  sherry,  have  very  similar  effects.  On  the  other  hand,  brandy,  whisky,  and 
gin  in  greater  amounts  almost  always  lessen  the  respiratory  changes,  and,  consequently, 
the  amount  of  the  gas  exhaled.  This  is  primarily  due  to  their  influence  on  the  rate  of 
metabolism  in  each  instance. 

Exercise.  Bodily  exercise,  in  moderation,  increases  the  quantity  of  CO2  expired  by  at 
least  one-third  more  than  it  is  during  rest.  For  about  an  hour  after  exercise  the  volume 
of  the  air  expired  in  the  minute  is  increased  nearly  2,000  c.c,  or  118  cubic  inches;  and  the 
quantity  of  carbon  dioxide  about  125  c.c,  or  7.8  cubic  inches  per  minute.  Violent  exercise, 
such  as  full  labor  or  athletic  competition,  still  further  increases  the  amount  of  the  carbonic 
acid  exhaled. 

The  Oxygen  is  Diminished.  Pettenkofer  and  Voit  have  found  that  the 
mean  consumption  of  oxygen  during  24  hours,  by  a  man  weighing  70  kilos, 
is  about  700  grams  or  490  liters.  The  quantity  of  oxygen  absorbed  increases 
with  muscular  exercise,  and  falls  during  rest.  In  general  terms  the  quantity 
absorbed  varies  with  the  activity  of  the  metabolic  processes,  following  very 
closely  the  variation  of  carbon  dioxide  under  the  conditions  outlined  above. 

The  Volume  of  the  Respired  Air  is  Diminished.  When  allowance  has 
been  made  for  the  expansion  in  heating,  the  volume  of  expired  air  is  decreased.. 


266  RESPIRATION 

the  loss  being  due  to  the  fact  that  a  portion  of  the  oxygen  absorbed  is  in  t 
returned  in  the  form  of  carbon  dioxide.  Since  the  oxygen  of  a  given  volun.c 
of  carbon  dioxide  would  have  the  same  volume  as  the  carbon  dioxide 
itself  at  a  given  temperature  and  pressure,  a  portion  of  the  oxygen  absorbed 
must  be  used  for  other  purposes  than  the  formation  of  carbon  dioxide. 
In  fact,  some  of  it  is  used  in  the  formation  of  urea,  some  in  the  formation 
of  water,  etc.  The  oxygen  in  the  carbon  dioxide  exhaled,  divided  by  the 
oxygen  absorbed,   gives  what  is  known    as    the    respiratory  quotient ;  thus 

CO     exhaled 


O      absorbed 
Normally  in  man  on  a  mixed  diet  the  respiratory  quotient  is 

4.0  to  4.5 

=    O.8   tO  O.Q. 

5 

But  it  is  subject  to  variation  through  several  causes.  For  example,  through 
variation  in  diet.  On  a  pure  carbohydrate  diet  the  respiratory  quotient 
will  rise  above  0.9,  i.e.,  to  1.0,  since  carbohydrates  contain  enough  oxygen 
to  oxidize  the  hydrogen  in  their  molecule.  On  a  diet  containing  much  fat 
it  is  lowest,  since  relatively  more  oxygen  is  needed  completely  to  oxidize  fat. 
The  theoretical  respiratory  quotient  for  fats  is  0.7.  The  same  is  true,  but  to 
a  less  degree,  in  the  case  of  proteids  which  also  require  much  oxygen  for  their 
complete  oxidation.  Muscular  exertion  raises  the  respiratory  quotient,  because 
in  its  performance  carbohydrates  are  used  up  in  relatively  greater  quantity. 

The  Watery  Vapor  in  Respired  Air  is  Increased.  The  quantity  emitted 
is,  as  a  general  rule,  sufficient  to  saturate  the  expired  air,  or  very  nearly  so. 
Its  absolute  amount  is,  therefore,  influenced  by  the  following  circumstances: 
1,  By  the  quantity  of  air  respired;  for  the  greater  this  is,  the  greater  also 
will  be  the  quantity  of  moisture  exhaled;  2,  By  the  quantity  of  watery 
vapor  contained  in  the  air  previous  to  its  being  inspired;  because  the  greater 
this  is,  the  less  will  be  the  amount  to  complete  the  saturation  of  the  air;  3, 
By  the  temperature  of  the  expired  air;  for  the  higher  this  is,  the  greater  will 
be  the  quantity  of  watery  vapor  required  to  saturate  the  air;  4,  By  the  length 
of  time  which  each  volume  of  inspired  air  is  allowed  to  remain  in  the  lungs; 
for  although,  during  ordinary  respiration,  the  expired  air  is  always  saturated 
with  watery  vapor,  yet,  when  respiration  is  performed  very  rapidly,  the  air 
has  scarcely  time  to  be  raised  to  the  highest  temperature  or  be  fully  charged 
with  moisture  ere  it  is  expelled. 

The  quantity  of  water  exhaled  from  the  lungs  in  24  hours  ranges  (accord- 
ing to  the  various  modifying  circumstances  already  mentioned)  from  about 
200  to  800  c.c,  the  ordinary  quantity  being  about  400  to  500  c.c.  Some  of 
this  is  probably  formed  by  the  chemical  combination  of  oxygen  with  hydro- 
gen in  the  system;  but  the  far  larger  proportion  of  it  is  water  which  has  been 


PRESSURE    AND    DIFFUSION    OF    THE    AIR  267 

absorbed,  as  such,  into  the  blood  from  the  alimentary  canal,  and  which  is 
exhakd  from  the  surface  of  the  air-passages  and  cells,  as  it  is  from  the  free 
surfaces  of  all  moist  animal  membranes,  particularly  at  the  high  tempera- 
ture of  warm-blooded  animals. 

A  Small  Quantity  of  Ammonia  is  added  to  the  ordinary  constituents  of 
expired  air.  It  seems  probable,  however,  both  from  the  fact  that  this  sub- 
stance cannot  be  always  detected  and  from  its  minute  amount  when  present, 
that  the  whole  of  it  may  be  derived  from  decomposing  particles  of  food  left 
in  the  mouth,  or  the  teeth,  and  that  it  is,  therefore,  only  an  accidental  con- 
stituent of  expired  air. 

The  Quantity  oj  Organic  Matter  in  Expired  Air  is  Increased.  It  was 
formerly  supposed  that  this  organic  matter  was  injurious  and  gave  rise  to 
the  unpleasant  symptoms  which  are  experienced  in  badly  ventilated  rooms. 
But  this  has  been  strongly  questioned  so  that  the  matter  cannot  be  considered 
settled  at  the  present  time. 

THE    RESPIRATORY    CHANGES    IN    THE    BLOOD. 

Pressure  and  Diffusion  of  the  Air.  It  must  be  remembered  that 
the  tidal  air  in  the  lungs  amounts  only  to  from  300  to  500  c.c.  at  each  in- 
spiration. This  amount  at  once  mixes  with  the  reserve  and  the  residual 
air  already  in  the  lungs.  The  mixture  is  facilitated  by  the  air  currents  set 
up  in  the  deeper  parts  of  the  lungs  by  the  sudden  entrance  of  the  tidal  air; 
but,  after  all  is  considered,  it  will  be  found  that  diffusion  is  the  greatest  factor 
in  producing  a  uniform  mixture  of  the  gases  in  the  alveoli  and  in  the  air-cells 
of  the  lungs.  Just  as  a  fresh  supply  of  oxygen  introduced  within  the  door 
of  a  closed  room  will  quickly  diffuse  throughout  the  space  of  the  entire  room 
so  will  the  fresh  tidal  air  diffuse  into  the  space  of  the  lungs.  When  the 
tidal  air  is  expired  its  average  composition  has  been  changed  so  it  has  only 
about  16  per  cent  of  oxygen  instead  of  the  usual  20.96  per  cent  of  oxygen  in 
air.  The  oxygen  content  of  the  air  still  left  in  the  lungs  is  probably  some- 
what less  than  the  percentage  in  this  expired  air  for  the  reason  that  the  air 
of  the  respiratory  tree,  the  trachea,  bronchi,  and  bronchioles,  is  never  fully 
mixed  with  the  alveolar  air. 

The  partial  pressure  of  the  oxygen  of  the  air  measured  under  standard 
conditions  is  159  mm.  of  mercury,  that  is,  20.96  per  cent  of  760  mm.  of  mer- 
cury, the  standard  pressure  of  one  atmosphere.  The  partial  oxygen  pressure 
in  expired  air  with  16  per  cent  of  oxygen  is  only  122  mm.  of  mercury.  These 
figures  show  a  diffusion  pressure  of  at  least  37  mm.  of  mercury  to  carry 
oxygen  into  the  deeper  recesses  of  the  lungs.  The  constant  loss  of  oxygen 
to  the  blood  probably  keeps  the  mean  difference  greater. 

The  Gases  of  the  Blood.  Turning  now  to  the  consideration  of 
the  gases  of  the  blood  in  the  lungs,  a  somewhat  different  picture  presents 


-,'»;s 


I  RATION 


itself.  The  blood  is  a  mass  of  corpuscles  floating  in  the  fluid  plasma.  An 
analysis  of  the  blood  shows  that  it  contains  oxygen,  carbon  dioxide,  and 
nitrogen,  the  gases  of  the  air.  The  usual  method  is  completely  to  extract 
the  blood  gases  by  an  air-pump,  figure  237,  and  determine  the  quantities  in 
cubic  centimeters  per  100  c.c.  of  blood. 

The  Extraction  of  the  Cases  from  the  Blood.  As  the  ordinary  air-pumps  are  not  suf- 
ficiently powerful  for  the  purpose,  the  extraction  of  the  gases  from  the  blood  is  accomplished 
bv  means  of  a  mercurial  air-pump,  of  which  there  are  many  varieties,  those  of  Ludwig, 
Alvergnidt,  Geissler,  and  Sprengel  being  the  chief.  The  principle  of  action  in  all  is  much 
the  same.     Ludwig's  pump,  which  may  be  taken  as  a  type,  is  represented  in  figure  237. 

It  consists  of  two  fixed  glass  globes,  C  and  F,  the  up- 
per one  communicating  by  means  of  the  stopcock,  D, 
and  a  stout  India-rubber  tube  with  another  glass  globe, 
L,  which  can  be  raised  or  lowered  by  means  of  a  pul- 
ley; it  also  communicates  by  means  of  a  stopcock,  B, 
and  a  bent  gU«re  tube,  A ,  with  a  gas  receiver  (not  repre- 
sented in  the  figure),  A  dipping  into  a  bowl  of  mercury, 
so  that  the  gas  may  be  received  over  mercury.  The 
lower  globe,  F,  communicates  with  C  by  means  of  the 
stopcock,  E,  with  f  in  which  the  blood  is  contained  by 
the  stopcock,  G,  and  with  a  movable  glass  globe,  if, 
■amilaT  to  L,  by  means  of  the  stopcock,  H,  and  the 
stout  India-rubber  tube,  K. 

In  order  to  work  the  pump,  L  and  if  are  filled 
with  mercury,  the  blood  from  which  the  gases  ire  to 
be  extracted  is  placed  in  the  bulb  7,  the  stopcocks  H, 
E,  D,  and  B  being  open,  and  G  dosed,  if  is  raised 
by  means  of  the  pulley  until  F  is  full  of  mercur 
the  air  is  driven  out.  E  is  then  closed,  and  L  is  raised 
so  that  C  becomes  full  of  mercury,  and  the  air  driven 
on.  B  is  then  closed.  On  lowering  L  the  mercury 
rur.-  :--.  :.:'.-  -  C,  ind  -  ra  umn  is  established  in  C. 
On  opening  E  and  lowering  if,  a  vacuum  is  similarly 
established  in  F  ;  if  G  be  now  opened,  the  blood  in  /  will 
enter  ebullition,  and  the  gases  will  pass  off  into  F  and  C, 
and  on  raising  if  and  then  L,  the  stopcock  B  being 
opened,  the  gas  is  driven  through  A,  and  is  received 
into  the  receiver  over  mercury.  By  repeating  the  ex- 
periment several  times  the  whole  of  the  gases  of  the 
-_-.=:  i:   -:-.     :      .    .Li-.      ■.:-.'.■:'-■  -~.  L  ::  ./     .  .  -\:r;.iv.  :. 

Pfluger's  analysis  of  the  arterial    blcn 

the  dog  gave  the  following  volumes  per  cent: 

gen  22.6.  carbon  dioxide  34.3,  and  nitrogen 

1.8.     The  analysis  for  the  venous  blood  gives 

much  lower  oxygen  and  a   higher  carbon    dioxide  per    cent.     The 

average  oxygen  con:-/     :'   venous  blood  is  ic  to  12  per  cent  and  the  carbon 

dioxide  45  per  cent.     The  blood  in  different  veins  of  the  body  varies  within 

wide  limits  as  regards  its  gas  content. 


I        :::. — L-a-d-wi^'s  Gis-7.ump. 


100  cc.  Arterial  bloc 
100  cc.  Venous  blood. 


Oxygen. 
22.6  c.c- 

12.      CC 


".  --      r. 

Di  xide. 

34  CC 

45  c-c 


1.7  cc 

-   - 


COMBINING     POWER     OF     HEMOGLOBIN    WITH     OXYGEN  *2G9 

The  large  quantity  of  oxygen  found  in  arterial  and  in  venous  blood  is  the 
more  striking  when  the  facts  of  absorption  of  gases  by  liquids  are  reviewed. 
A  liquid  such  as  water  will,  when  exposed  to  a  gas,  take  up  the  gas  by  absorp- 
tion according  to  definite  physical  laws.  Under  constant  temperature  the 
amount  of  gas  absorbed,  oxygen  for  example,  varies  directly  as  the  pressure 
of  the  gas,  or  partial  pressure  if  the  gas  is  a  mixture.  The  oxygen  absorbed 
by  water  from  pure  air  as  compared  with  expired  air  is  in  direct  proportion 
to  the  partial  pressure  of  oxygen  in  the  two  airs,  which  is  as  159  to  122. 

The  amount  of  gas  absorbed  for  a  unit  of  fluid  under  standard  tempera- 
ture and  pressure  (one  atmosphere  at  o°  C),  called  its  absorption  coefficient, 
is  about  the  same  for  blood-plasma  as  for  water.  Before  one  can  determine 
the  actual  amount  of  oxygen  in  (he  plasma,  the  tension  or  absorption  pressure 
must  be  determined. 

The  tension  of  the  oxygen  in  arterial  blood  is  found  by  an  instrument 
which  enables  one  to  measure  the  pressure  at  which  oxygen  is  neither  ab- 
sorbed nor  given  off.  The  instrument  commonly  used  is  called  an  aerotonom- 
eter.  The  principle  of  the  instrument  depends  upon  the  fact  that  blood 
exposed  to  mixtures  of  the  gases  in  air  tends  to  give  up  or  absorb  gases  from 
the  air  until  complete  equilibrium  is  established. 

By  this  means  observers  have  measured  the  tensions  of  the  blood  gases. 
The  results  have  not  been  very  constant,  but  the  oxygen  tension  has  been 
found  to  be  from  4  (Strassburg)  to  10  (Herter)  per  cent  of  an  atmosphere. 
Many  determinations  have  been  given  of  both  lower  and  higher  percentages, 
but.  accepting  the  above  limits  for  a  working  average,  the  oxygen  tension 
in  arterial  blood  would  be  from  30.4  to  76  mm.  of  mercury. 

Blood-plasma  exposed  to  an  air  with  a  partial  pressure  of  30.4  to  76  mm. 
of  mercury  would  absorb  only  from  0.1  to  0.3  (0.26  c.c.  Pfliiger)  of  a  cubic 
centimeter  of  oxygen  for  100  c.c.  of  blood.  As  a  matter  of  fact,  100  c.c.  of  whole 
blood  contains  from  20  to  22  c.c.  of  oxygen.  It  is  evident  that  blood  cannot 
hold  the  oxygen  in  simple  solution,  but  must  retain  it  in  chemical  combina- 
tion. The  red  blood-corpuscles  have  been  shown  to  carrv  the  excess  of 
oxygen  by  virtue  of  the  special  respirator}'  pigment,  hemoglobin. 

Combining  Power  of  Hemoglobin  with  Oxygen.  One  hundred 
cubic  centimeters  of  blood  contain  about  14  grams  of  hemoglobin,  page  120. 
Each  gram  of  hemoglobin,  when  fully  saturated  with  oxygen,  according  to 
Hiifner's  earlier  determination,  combines  with  1.56  c.c.  of  oxygen.  By  later 
more  careful  work  he  gets  the  determination  of  1.34  c.c.  for  hemoglobin  of 
ox  blood.  This  last  figure  indicates  that  the  combining  power  of  the  hemo- 
globin is  dependent  upon  the  iron  in  the  molecule,  in  which  one  atom  of  iron 
combines  with  one  atom  of  oxygen.  The  later  investigation  of  the  conditions 
under  which  hemoglobin  combines  with  oxygen  are  by  Hiifner,  on  the  one 
hand,  and  Loewy,  on  the  other.  The  former  worked  with  purified  solutions 
of  hemoglobin,  the  latter  with  blood.     The  average  results  of  the  investigations 


270  RESPIRATION 

of  these  two  observers  show  that  when  the  oxygen  tension  in  the  air,  which  is  in 
contact  with  the  blood,  is  lowered  below  a  certain  point,  the  amount  of  oxygen 
which  will  be  liberated  from  combination  with  hemoglobin  will  be  very  great, 
whereas  a  lowering  of  the  tension  of  oxygen  by  an  equal  amount  where  the 
pressures  are  relatively  high  leads  to  practically  no  liberation  of  hemoglobin, 
and  the  converse  is  equally  true.  The  critical  oxygen  pressure  in  so  far  as 
its  combination  with  hemoglobin  is  concerned  varies  according  to  observers. 
With  Loewy  the  critical  dissociation  pressure  is  at  or  below  76  mm.  of  mer- 
cury, 10  per  cent  of  an  atmosphere.  Strassburg  gives  the  oxygen  tension  of 
arterial  blood  as  29.64  mm.  of  mercury,  and  for  venous  blood  22.04  mm.  of 
mercury.  That  is  to  say,  during  the  brief  interval  in  which  the  blood  is 
in  the  pulmonary  capillaries  the  oxygen  tension  has  increased  by  7.6  mm. 
of  mercury,  an  increase  of  tension  which  would  produce  very  little  increase 
in  simple  absorption  of  oxygen.  Yet  is  it  sufficient  to  cause  fixation  of 
from  four  to  five  volumes  per  cent  of  oxygen  by  the  hemoglobin. 

Oxygen  Pressure  in  the  Atmosphere 159        mm.  of    mercury 

I 
"       Alveolar  air 122        mm.  of    mercury 

i 
"       Venous  blood 22.04  mm.  of   mercury 

It  is  evident  that  there  will  be  diffusion  of  oxygen  from  the  high  tension 
toward  the  lower  and  in  the  direction  indicated  by  the  arrows  in  the  table 
above.  As  fast  as  the  oxygen  diffuses  into  the  venous  blood,  thus  tending  to 
raise  the  pressure  of  the  gas  in  solution,  it  is  taken  up  and  fixed  by  the  hemo- 
globin. This  process  proceeds  during  the  interval  the  blood  is  fn  the  pul- 
monary capillaries  far  enough  to  raise  the  oxygen  tension  from  22.04  mm- 
of  mercury  to  29.64  mm.  of  mercury,  and  far  enough  to  permit  of  the  fixation 
of  from  four  to  five  volumes  per  cent  of  oxygen. 

Liberation  of  Oxygen  in  the  Tissue  Capillaries.  When  the  arterial 
blood  reaches  the  capillaries  of  the  tissues,  then  the  situation  which  we  have 
just  found  holding  good  in  the  lungs  is  reversed.  As  rapidly  as  the  oxygen 
reaches  the  living  protoplasm  of  the  tissues  it  enters  into  fixed  combination, 
thus  rendering  it  inert.  The  oxygen  tension  in  the  tissue  cells  will,  there- 
fore, be  zero.  Under  these  conditions  the  difference  in  pressure  level  be- 
tween the  oxygen  tension  in  the  blood  and  that  in  the  tissues  is  sufficient  to 
cause  a  rapid  diffusion  of  oxygen  through  the  capillary  walls  with  correspond- 
ing liberation  of  the  oxygen  from  the  hemoglobin  according  to  the  laws  of 
combination  given  in  the  table  above.  The  total  effect  of  this  process  is  to 
maintain  a  relatively  high  diffusion  pressure  of  the  oxygen  in  the  blood. 
During  the  time  the  blood  remains  in  the  capillaries  the  total  oxygen  tension 
will  have  been  lowered  from  29.64  to  22.04  mm-  °f  mercury,  yet  this  slight 
lowering  of  tension  is  sufficient  to  liberate  from  four  to  five  volumes  percent  of 
oxygen.     This  figure,  of  course,  is  comparative.     In  many  of  the  very  active 


ELIMINATION    OF     CARBON     DIOXIDE  271 

tissues,  such  as  in  muscle,  a  much  larger  per  cent  of  oxygen  will  have  been 
disassociated  and  the  oxygen  tension  correspondingly  lowered  so  that  the 
venous  blood  returning  through  such  an  active  organ  may  not  have  more 
than  half  the  average  amount  of  oxygen  found  in  venous  blood. 

Considering  the  pressure  relations  of  oxygen  from  the  time  of  its  intro- 
duction into  the  body  with  the  fresh  air  to  its  fixation  in  the  tissues  we  have 
the  following  schema: 

Oxygen  Pressure  in  the  Atmosphere 159    mm. 

I 
Alveolar  Air 122    mm. 

i 
Venous  Blood 22 .04  mm. 

Tension  of  Oxygen  in  the  Arterial  Blood 29.64  mm. 

"       "     "    Tissues o.oomm. 

Elimination  of  Carbon  Dioxide  by  the  Blood  and  the  Respiratory 
Apparatus.  The  principles  of  absorption  of  gas  by  liquids  discussed 
in  the  preceding  pages  apply  equally  well  for  carbon  dioxide  with  the  exception 
that  carbon  dioxide  is  about  three  times  as  soluble  in  blood  as  is  oxygen. 
The  carbon  dioxide  results  from  the  oxidative  processes  going  on  in  the  tis- 
sues, and  this  gas  is  present  in  large  quantities  in  the  tissues  and  their  im- 
mediately surrounding  lymph.  An  analysis  of  the  carbon-dioxide  content 
of  venous  blood  reveals  the -presence  of  about  45  c.c.  of  the  gas  in  100  c.c.  of 
blood.  This  gas,  like  oxygen,  is  held  in  such  large  quantity  by  virtue  of  the 
fact  that  it  forms  loose  chemical  combinations  in  the  blood.  Of  the  total 
quantity  not  more  than  5  per  cent  is  held  in  simple  solution.  From  10  to 
15  per  cent  of  the  total  volume  is  found  in  firm  combination  in  such  forms 
as  carbonates,  bicarbonates,  etc.  The  remaining  80  and  more  volumes 
per  cent  is  held  in  loose  chemical  combination,  a  combination  which  is  broken 
up  under  the  same  conditions  of  variation  in  carbon-dioxide  tension  as  were 
found  to  exist  for  oxygen  in  combination  with  hemoglobin.  In  the  case  of 
carbon  dioxide  an  analysis  of  plasma  reveals  the  fact  that  the  gas  is  in  com- 
bination with  some  compound  of  the  plasma,  probably  a  proteid.  In  fact, 
there  is  some  evidence  to  show  that  carbon  dioxide  combines  with  the  globulin 
group.  Carbon  dioxide  also  forms  loose  chemical  compounds  with  the  con- 
stituents of  the  red  corpuscles,  probably  with  the  proteid  portion  of  the  hemo- 
globin molecule.  The  pressure  relations  of  this  gas  as  regards  its  diffusion 
in  the  process  of  elimination  are  shown  in  the  following  table: 

Carbon-dioxide  Tension  in  the  Tissues 58  mm.  of  mercury 

1 
"         "        Venous  Blood 41       "      " 

1 
"  "  "        Alveolar  Air 23  to  38  mm.  of  " 

I 
"  "  "  "        Expired   Air 5.8  mm.        "     " 


272  RESPIRATION 

Theories  of  Interchange  of  Gases  in  the  Lungs  and  in  the  Tissues. 
The  above  discussion  is  on  the  basis  of  the  mechanical  interpretation  of  the 
transfer  of  gases  in  the  lungs  and  in  the  tissues.  By  this  theory  it  is  assumed 
that  the  oxygen  passes  from  the  air  in  the  lungs  through  the  moist  pulmonary 
membrane  of  the  alveoli  to  the  capillary  walls  into  the  blood-plasma,  obeying 
the  physical  laws  of  gas  diffusion.  Likewise  in  the  tissues  this  theory  pre- 
supposes the  difference  in  the  mechanical  tension  in  the  capillary  blood- 
plasma,  the  lymph,  and  the  living  tissue  will  lead  to  diffusion  of  the  oxygen 
in  the  direction  of  lowest  pressure. 

Some  facts  have  indicated  that  we  cannot  account  for  the  transference 
of  oxygen  by  the  purely  mechanical  theory.  The  idea  has  been  advanced 
that  the  living  epithelial  wall  of  the  lung,  as  well  as  that  of  the  capillary,  exerts 
a  distinct  influence  on  the  passage  of  oxygen  of  such  nature  as  might  be  re- 
garded as  a  secretion  of  this  gas.  This  theory  finds  some  additional  support 
in  the  fact  that  in  the  air  bladders  of  certain  fishes  a  distinct  secretion  of  oxygen 
has  been  proven. 

THE  NERVOUS  REGULATION  OF  THE  RESPIRATORY 
APPARATUS. 

Like  all  other  functions  of  the  body  the  discharge  of  which  is  necessary 
to  life,  the  respiratory  movement  is  essentially  an  involuntary  act.  Unless 
this  were  the  case,  life  would  be  in  constant  danger,  and  would  cease  on  the 
loss  of  consciousness  for  a  few  moments,  as  in  sleep.  It  is,  however,  of  ad- 
vantage to  the  body  that  respiration  should  be  to  some  extent  under  the 
control  of  the  will.  For,  were  it  not  so,  it  would  be  impossible  to  perform 
those  respiratory  acts  such  as  speaking,  singing,  and  the  like. 

The  Respiratory  Nerve  Center.  It  has  been  known  for  centuries 
that  there  exists  a  region  of  the  central  nervous  system  on  the  destruction  of 
which  both  respiration  and  life  cease.  Flourens,  1842,  after  many  series 
of  experiments  as  to  the  exact  position  of  what  he  called  the  "knot  of  life" 
{nosud  vital),  placed  it  in  the  fourth  ventricle,  at  the  point  of  the  V  in  the 
gray  matter  at  the  lower  end  of  the  calamus  scriptorius;  a  district  of  consider- 
able size,  5  mm.,  on  both  sides  of  the  middle  line.  Observers  subsequent  to 
Flourens  have  attempted  to  show  that  the  chief  respiratory  center,  on  the 
one  hand,  is  situated  higher  up  in  the  nervous  system,  in  the  floor  of  the  third 
ventricle  (Christiani),  or  in  the  corpora  quadrigemina  (Martin  and  Booker, 
Christiani,  and  Stanier),  or  lower  down  in  the  spinal  cord.  The  balance 
of  experimental  evidence,  however,  is  to  prove  that  the  sole  centers  for  respira- 
tion are  in  a  limited  district  in  the  medulla  oblongata  in  close  connection  with 
the  vagus  nucleus  on  each  side,  with  which  they  are  probably  identical. 
The  destruction  of  this  region  stops  respiration.  If  the  center  be  left  in 
connection  with  the  muscles  of  respiration  by  their  nerves,  although  the 


THE    RESPIRATORY     NERVE     CENTER  273 

remainder  of  the  central  nervous  system  be  separated  from  it,  respiration 
continues.  It  may  be  considered  almost  certain  that  the  medullary  center 
is  the  only  true  respiratory  center.  Langendorff  states  that  in  newly  born 
animals  in  which  the  medulla  has  been  immediately  cut  across  at  a  level  a 
few  millimeters  below  the  point  of  the  calamus  scriptorius,  respiration  con- 
tinues for  some  time,  but  this  is  questionable.  Normal  respiration  does 
not  occur  after  separation  of  the  bulb  from  the  cord,  and  the  so-called 
respiratory  movements  noticed  by  Langendorff  are  merely  tetanic  contrac- 
tions of  the  respiratory  muscles  in  which  often  enough  other  muscles  take 
part. 

The  action  of  the  medullary  center  is  to  send  out  impulses  during  in- 
spiration, which  cause  contractions  of  the  inspiratory  muscles- — a,  of  the 
nostrils  and  jaws,  through  the  facial  and  inferior  division  of  the  fifth  nerves; 

b,  of  the  glottis,  chiefly  through  the  inferior  laryngeal  branches  of  the  vagi; 

c,  of  the  intercostal  and  other  muscles  which  produce  raising  of  the  ribs, 
chiefly  through  the  intercostal  nerves,  and  d,  of  the  diaphragm,  through  the 
phrenic  nerves.  If  any  one  of  these  sets  of  nerves  be  divided,  respiratory 
movements  of  the  corresponding  muscles  cease.  Similarly  it  may  be  supposed 
that  the  center  sends  out  impulses  during  expiration  to  certain  other  muscles. 
It  has  been  suggested,  however,  that  the  center  is  double,  that  it  is  made  up 
of  inspiratory  cells  which  are  constantly  in  action,  and  of  an  expiratory  group 
of  cells  which  act  less  generally,  inasmuch  as  ordinary  tranquil  expiration 
is  seldom  more  than  an  elastic  recoil,  and  not  a  muscular  act  to  any  marked 
degree. 

The  respiratory  center  is  also  bilateral,  as  has  been  proven  by  the  method 
of  antero-posterior  section  of  the  medulla.  The  tracts  from  each  half  of  the 
center  are  separate  and  distinct.  If  the  cervical  cord  be  split  into  a  right 
and  left  half,  and  one  side  sectioned  at  the  level  of  the  second  cervical  verte- 
bra, then  the  respiratory  movements  of  that  side  of  the  diaphragm  cease 
while  on  the  opposite  side  they  continue  their  rhythm. 

Assuming  this  view  of  the  quadruple  nature  of  the  respiratory  centers 
to  be  correct,  there  is  some  difference  of  opinion  of  the  exact  mode  of  action; 
it  is  thought  that  the  center  may  act  automatically,  but  normallv  is  influenced 
by  afferent  impulses  from  the  periphery,  as  well  as  by  impulses  passing  down 
from  the  cerebrum.  The  center  is,  in  other  words,  both  automatic  and 
reflex.     It  will  be  simplest  to  discuss  its  reflex  function  first. 

Action  of  Afferent  Stimuli  on  the  Respiratory  Rhythm.  Action 
of  the  vagi.  If  both  vagi  be  divided  in  the  neck,  the  respirations  become 
much  slower  and  deeper.  This  may  be  the  case,  but  to  a  less  marked  degree, 
if  one  of  the  nerves  is  divided  instead  of  both.  If  the  central  end  of  the 
divided  nerve  be  stimulated  with  a  weak  but  properly  adjusted  strength  of 
interrupted  current,  the  effect  is  that  the  respirations  are  quickened,  and  if 
the  stimuli  are  properly  regulated  the  normal  rhythm  of  respiration  may 
18 


274  RESPIRATION 

be  resumed.  II"  the  stimuli  be  repeated  with  stronger  currents,  the  breathing 
is  brought  to  a  standstill,  sometimes  at  the  height  of  inspiration,  by  tetanus 
of  the  diaphragm.  Usually,  however,  stimulation  of  the  central  end  of  the 
divided  vagus  produces  still  greater  slowing  than  that  which  follows  the  division 
so  that  the  respirations  (ease  with  the  diaphragm  in  a  condition  of  complete 
relaxation. 

The  action  of  the  vagus  may  be  to  tall  forth  either  inspiration  or  expira- 
tion— the  impulses  passing  up  the  vagi  being  necessary  to  the  production 
of  the  normal  respiratory  rhythm.  The  fibers  of  the  vagus  are  used  under 
the  following  circumstances:  those  libers  which  tend  to  inhibit  expiration 
and  to  stimulate  inspiration  are  stimulated  at  their  origin  in  the  lung  when  the 

an.  off 


^J^KhKkSAL 


,^irnif( .,,ii,  |  iiih lir^'iH   |H|i  |lii)»i   i 


Fig.  239. — The  Effect  of  Stimulating  the  Vagus  Nerve  on  Respiratory  Rate.  The  stimulus 
was  applied  between  the  points  "  on  "  and  "  off."  The  inhibition  lasts  some  seconds  after  the  stim- 
ulus is  removed.     Time  in  seconds.     The  intratracheal  pressure  is  recorded. 

lung  is  empty  and  in  a  condition  of  expiration,  and  the  fibers  which  tend 
to  inhibit  inspiration  and  to  promote  expiration  are  stimulated  when  the 
lung  is  fully  expanded.  The  afferent  impulses  by  this  view  are  the  results 
of  mechanical  stimulation,  and  do  not  depend  altogether  upon  the  chemical 
nature  of  the  gases  within  the  pulmonary  alveoli. 

Action  of  the  Superior  Laryngeal  Nerves.  If  the  superior  laryngeal 
branch  of  the  vagus  be  divided,  which  usually  produces  no  apparent  effect, 
and  the  central  end  be  stimulated,  the  effect  is  very  constant, — respirations 
are  slowed,  but  there  is  a  tendency  toward  expiration,  as  is  shown  by  the 
contraction  of  the  abdominal  muscles.  Thus,  the  vagus  contains  fibers 
which  stimulate  inspiration  and  inhibit  expiration,  as  well  as  other  fibers 
which  have  the  reverse  effect;  while  the  superior  laryngeal  fibers  inhibit  in- 
spiration and  stimulate  expiration. 

The  superior  laryngeal  nerves  are  true  expiratory  nerves,  and  are  nor- 
mally set  in  action  when  the  mucous  membrane  of  the  larynx  is  irritated. 
They  are  not  in  constant  action  like  the  vagi. 

Action  of  the  Glosso-pharyngeal  Nerves.  It  has  been  ascertained, 
by  the  researches  of  Marckwald,  that  while  division  of  the  glosso-pharyngeal 
nerves  produces  no  effect  upon  respiration,  stimulation  of  them  causes  in- 
hibition of  inspiration  for  a  short  period.  This  action  accounts  for  the  very 
necessary  cessation  of  breathing  during  swallowing.  The  effect  of  the  stimu- 
lation is  only  temporary,  and  is  followed  by  normal  breathing  movements. 

Action   of   Other   Sensory  Nerves.     The   respiratory  center  is  in- 


AUTOMATIC     ACTION     OF    THE     RESPIRATORY     CENTERS  275 

fluenced  strongly  by  afferent  nerve  impulses  having  their  origin  in  general 
sensory  nerves,  particularly  the  nerves  of  the  skin.  Cold  water  suddenly 
applied  to  the  surface  of  the  skin  is  almost  invariably  followed  by  a  deep 
inspiration.  Stimulation  of  the  splanchnics  and  of  the  abdominal  branches 
of  the  vagi  produces  expiration.  Stimulation  of  the  isolated  sciatic  nerve  of 
the  dog  or  the  rabbit  causes  a  marked  acceleration  both  of  the  rate  and 
the  amplitude  of  the  respiratory  movements,  see  figure  246.  This  accelera- 
tion is  due  to  afferent  impulses  which  reach  the  respiratory  center  in  the  me- 
dulla over  sensory  paths,  paths  which  are  not  necessarily  special  respiratory 
afferent  paths,  but  rather  are  general  afferent  paths  which  affect  the  respira- 
tory center  through  their  numerous  collaterals  in  the  brain  stem. 

It  must  be  remembered  that,  although  on  stimulation  many  sensory  nerves 
may  be  made  to  produce  an  effect  upon  the  respiratory  centers,  there  is  no 
evidence  to  show  that  any  one  of  them,  except  the  vagi,  is  constantly  in  action. 
The  vagi  indeed  are,  as  far  as  we  know,  the  normal  regulators  of  respiratory 
movements,  yet  one  must  remember  that  it  is  possible  reflexly  to  influence 
the  respiration  rate  and  depth  through  reflexes  that  may  have  their  sensory 
origin  in  any  part  of  the  body. 

The  respiratory  center  is  also  influenced  by  nerve  activity  of  the  cerebral 
cortex,  psychic  activity.  This  is  illustrated  by  the  limited  voluntary  control 
of  the  respiration  movements. 

Automatic  Action  of  the  Respiratory  Centers.  Although  it  has 
been  very  definitely  proved  that  the  respiratory  centers  may  be  affected  by 
afferent  stimuli,  and  particularly  by  those  reaching  them  through  the  vagi, 
there  is  reason  for  believing  that  the  center  is  capable  of  sending  out  efferent 
impulses  to  the  respiratory  muscles  without  the  action  of  any  afferent  stimuli. 
Thus,  if  the  brain  be  removed  above  the  bulb,  respiration  continues.  If  the 
spinal  cord  be  divided  immediately  below  the  bulb,  the  facial  and  laryngeal 
respiratory  movements  continue,  although  no  afferent  impulses  can  reach 
the  center  except  through  the  cranial  sensory  nerves,  and  these  indeed  may 
be  divided  without  producing  any  effect,  when  the  bulb  and  cord  are  intact. 
As  has  been  shown,  too,  respiration  continues  when  the  vagi  are  divided. 
Isolation  of  the  respiratory  center  from  its  sensory  relations  does  not  destroy 
respiratory  movements  so  long  as  the  motor  paths  through  the  phrenic  nerve 
are  intact.  All  of  these  experiments  render  it  highly  probable  that  afferent 
impulses  are  not  required  in  order  that  the  respiratory  centers  should  send 
out  efferent  impulses  to  the  respiratory  muscles.  The  center,  then,  is  auto- 
matic. 

Method  of  Automatic  Stimulation  of  the  Respiratory  Center.  The 
respiratory  center  is  capable  of  working  automatically  apart  from  afferent 
impulses,  and  this  fact  has  been  explained  by  the  supposition  that  it  is  stimu- 
lated to  action  by  the  condition  of  the  blood  circulating  through  it.  When 
the  blood  becomes  more  and  more  venous  the  action  of  the  center  becomes 


270  RESPIRATION 

more  and  more  energetic,  and  if  the  air  is  prevented  from  entering  the  chest, 
the  respiration  in  a  short  time  becomes  very  labored.  If  the  aeration  of  the 
blood  is  much  interfered  with,  not  only  are  the  ordinary  respiratory  muscles 
employed,  but  also  those  muscles  of  extraordinary  inspiration  and  expira- 
tion which  have  been  previously  enumerated.  Thus,  as  the  blood  becomes 
more  and  more  venous,  and  by  venous  we  mean  that  the  blood  contains  a 
relatively  large  amount  of  carbon  dioxide  and  a  diminished  amount  of  oxygen, 
the  action  of  the  medullary  center  becomes  more  and  more  profound.  The 
question  has  been  much  debated  as  to  what  quality  of  the  venous  blood  it  is 
which  causes  this  increased  activity;  whether  it  ;s  its  deficiency  of  oxygen 
or  its  excess  of  carbon  dioxide.  It  has  been  answered  to  some  extent  by  ex- 
periments which  offer  no  obstruction  to  the  exit  of  carbon  dioxide,  as  when 
an  animal  is  placed  in  an  atmosphere  of  nitrogen.  Under  these  conditions 
dyspnea  occurs,  showing  that  blood  which  contains  a  diminished  amount 
of  oxygen  stimulates  the  cells  of  the  respiratory  center.  On  the  other  hand, 
if  the  normal  amount  of  oxygen  is  supplied  while  the  carbon  dioxide  of  the 
blood  is  prevented  from  escaping  and  thus  allowed  to  accumulate  in  the 
blood,  there  is  also  a  great  increase  in  the  respiratory  activity  of  the  center; 
an  excess  of  carbon  dioxide  in  the  blood,  flowing  through  the  respiratory 
center,  stimulates  the  cells  to  greater  activity.  It  is  highly  probable,  there- 
fore, that  the  respiratory  centers  may  be  stimulated  to  action  both  by  the 
absence  of  sufficient  oxygen  in  the  blood  circulating  in  it,  and  by  the  presence 
of  an  excess  of  carbon  dioxide. 

These  facts  are  particularly  well  supported  by  the  experiments  of  Zuntz 
who  varied  the  oxygen  and  the  carbon-dioxide  content  of  the  air  breathed, 
and  measured  the  volume  breathed  per  minute.  When  the  oxygen  of  the 
air  breathed  was  reduced  by  10  to  50  per  cent,  the  air  breathed  was  increased 
only  slightly,  5  to  10  per  cent.  When  the  oxygen  of  the  air  was  reduced 
by  60  per  cent,  the  volume  of  air  breathed  was  increased  30  to  40  per  cent, 
and  even  more.  Other  observations  show  us  that  the  oxygen  in  the  blood 
in  these  experiments  will  fall  in  much  less  per  cent  than  the  reduction  in 
the  oxygen  of  the  air  would  lead  us  to  suspect. 

When  Zuntz  kept  the  oxygen  content  of  the  air  about  constant,  but  in- 
creased the  carbon-dioxide  content,  then  the  amount  of  air  breathed  was 
greatly  increased.  Air  containing  18.4  per  cent  of  oxygen  and  11.5  per  cent 
of  carbon  dioxide  increased  the  amount  breathed  per  minute  from  7.5  liters 
to  32.5  liters.  These  experiments  indicate  that  within  the  limits  of  the 
normal  variations  in  blood  the  carbon  dioxide  has  a  much  greater  influ- 
ence than  oxygen  on  the  irritability  of  the  cells  of  the  respiratory  center. 

But  this  is  not  all,  since  it  has  been  observed  by  Marckwald  that  the 
medullary  center  is  capable  of  acting  for  some  time  in  the  absence  of  any 
circulation,  and  after  excessive  bleeding.  The  view  taken  by  this  author 
with  regard  to  the  action  of  the  center  is  as  follows:   The  respiratory  center 


RESPIRATORY     MOVEMENTS     AT     BIRTH  277 

is  set  to  act  by  the  condition  of  its  metabolism,  much  in  the  same  way  as 
the  heart  is  set  to  beat  rhythmically.  When  anabolism  is  completed,  catab- 
olism  or  discharge  occurs,  and  this  alternate  but  crude  and  spasmodic 
action  will  occur  without  a  definite  blood  supply  so  long  as  the  centers  are 
properly  nourished  and  stimulated  by  their  own  intercellular  fluid.  It  is 
unreasonable  to  think,  however,  that  the  respiratory  center  is  independent 
of  the  character  of  the  blood  supply,  either  as  regards  quantity  or  quality 
of  the  blood.  It  has  also  been  shown  that  the  presence  of  the  products  of 
great  muscular  metabolism  in  the  blood  will  greatly  increase  the  irritability 
of  the  respiratory  center,  even  if  the  blood  itself  be  not  particularly  venous 
in  character. 

The  Establishment  of  Respiratory  Movements  at  Birth.  From 
the  preceding  paragraph  it  appears  that  the  regulation  of  the  respiratory 
movements  is  normally  due  to  the  automaticity  of  the  respiratory  center  as 
influenced,  first,  by  the  blood  flowing  through  it  and,  second,  by  the  afferent 
nerve  impulses  which  reach  the  center.  The  fetus  in  the  womb  is  supplied 
by  arterial  blood  from  the  blood-vessels  of  the  mother.  The  fetus  does  not 
ordinarily  give  respiratory  movements  before  birth,  but  it  may  be  made  to 
do  so  by  experimental  procedure.  At  birth  the  placental  circulation  is  sud- 
denly interrupted,  and  the  blood  rapidly  increases  in  venosity  until  the  skin, 
lips,  and  mucous  membranes  are  very  cyanotic  in  appearance.  It  is  at  this 
time  that  the  respiratory  center  begins  its  rhythmic  discharges,  being  aroused 
by  the  direct  stimulating  effects  of  the  strongly  venous  blood.  It  is  more 
than  possible  that  the  irritability  of  the  center  is  also  increased  by  the  stimu- 
lation of  the  skin  by  the  air,  the  contact  with  clothing,  and  the  hands  of  the 
nurse.  We  have  already  seen  that  cutaneous  stimulation  leads  to  increase 
in  both  respiratory  rate  and  amplitude  even  in  the  adult.  The  primary 
stimulus  for  the  establishment  of  the  respiratory  rhythm  at  birth,  then,  is 
the  venosity  of  the  blood,  but  this  cause  is  supported  by  the  general  reflexes 
which  reach  the  respiratory  center. 

Certain  Special  Types  of  Respiration.  Whatever  the  exact  quality 
of  the  venous  blood  which  excites  the  respiratory  center  to  produce  normal 
respirations,  there  can  be  no  doubt  that,  as  the  blood  becomes  more  and  more 
venous  from  obstruction  to  the  entrance  of  air  into  the  lung,  or  from  the 
blood  not  taking  up  from  the  air  its  usual  supply  of  oxygen,  the  respiratory 
center  becomes  either  less  or  more  active  and  excitable.  Conditions  ensue 
which  have  received  the  names  Apnea  (diminished  breathing),  Hyperpnea 
(excessive  breathing),  Dyspnea  (difficult  breathing),  and  Asphyxia  (suffoca- 
tion). 

Apnea.  This  is  a  condition  of  diminished  respiratorv  movement.  When 
we  take  several  deep  inspirations  in  rapid  succession  by  voluntary  effort, 
we  find  that  we  can  do  without  breathing  for  a  much  longer  time  than  usual; 
in  other  words,  several  rapid  respirations  seem  to  inhibit  for  a  time  normal 


278  RESPIRATION 

respiratory  movements.  The  reason  for  this  partial  cessation  of  respira- 
tion, or  apnea,  is  not  that  we  overcharge  our  blood  with  oxygen,  as  was  once 
thought,  for  Hering  has  shown  that  animals  in  a  condition  of  apnea  may 
have  less  oxygen  in  their  blood  than  in  a  normal  state,  although  the  carbon 
dioxide  is  less.  It  is  probable  that  the  cause  of  apnea  is  that  by  rapid  in- 
flations of  the  lungs  impulses  pass  up  by  the  vagi,  by  means  of  which  in- 
spiration is  after  a  while  inhibited;  or  that  by  the  repeated  stimulation  of 
the  center  by  vagus  impulses  which  result  in  rapid  respiratory  movements, 
anabolism  is  at  last  arrested.  Apnea  is  with  difficulty  produced,  if  at  all, 
when  the  vagi  are  divided. 

Asphyxia.  The  condition  of  stress  in  the  respiratory  apparatus  brought 
about  by  insufficient  respiratory  activity  leads  to  a  condition  of  asphyxia. 
Progressive  asphyxiation  may  be  brought  on  by  anything  which  interferes 
with  the  normal  interchange  of  the  respiratory  gases  of  the  blood. 

Asphyxia  may  be  produced  by  the  prevention  of  the  due  entry  of  oxygen 
into  the  blood,  either  by  direct  obstruction  of  the  trachea  or  other  part  of  the 
respiratory  passages,  or  by  introducing  instead  of  ordinary  air  a  gas  devoid 
of  oxygen,  or,  by  interference  with  the  due  interchange  of  gases  between 
the  air  and  the  blood. 

The  symptoms  of  asphyxia  may  be  divided  into  three  groups,  which 
correspond  with  the  stages  of  the  condition  which  are  usually  recognized; 
these  are:  i,  the  stage  of  exaggerated  breathing,  hyperpnea;  2,  the  stage  of 
convulsions,  dyspnea;   3,  the  stage  of  exhaustion,  asphyxiation. 

In  the  first  stage  the  breathing  becomes  more  rapid  and  at  the  same  time 
deeper  than  usual,  the  inspirations  at  first  being  especially  exaggerated  and 
prolonged.  This  is  soon  followed  by  a  similar  increase  in  the  expiratory 
efforts  being  aided  by  the  muscles  of  extraordinary  expiration.  This  stage  is 
usually  called  hyperpnea.  Hyperpnea  soon  passes  into  a  condition  of  labored 
breathing  in  which  there  is  marked  increase  of  the  force  of  the  expiratory 
as  well  as  the  inspiratory  act,  a  condition  described  as  dyspnea.  All  the 
muscles  capable  of  aiding  either  directly  or  indirectly  in  respiration  are  ulti- 
mately brought  into  action.  These  respiratory  convulsions  are  followed  by 
rather  sudden  onset  of  paralysis  of  the  respiratory  center  and  death. 

The  conditions  oj  the  vascular  system  in  asphyxia  are:  1,  more  or  less 
interference  with  the  passage  of  the  blood  through  the  systemic  and  the  pul- 
monary blood-vessels;  2,  accumulation  of  blood  in  the  right  side  of  the  heart 
and  in  the  systemic  veins;  3,  circulation  of  impure  (non-aerated)  blood  in 
all  parts  of  the  body,  especially  through  the  respiratory  center. 

Cheyne-Stokes'  breathing  is  a  rhythmical  irregularity  in  respirations  which 
has  been  observed  in  various  diseases.  Respirations  occur  in  groups;  at  the 
beginning  of  each  group  the  inspirations  are  very  shallow,  but  each  succes- 
sive breath  is  deeper  than  the  preceding,  until  a  climax  is  reached,  after  which 
the  inspirations  become  less  and  less  deep,  until  they  cease  altogether  for 


EFFECTS    OF    VITIATED     AIR  279 

a  time,  after  which  the  cycle  is  repeated.  This  phenomenon  appears  to  be 
due  to  the  want  of  action  of  some  of  the  usual  cerebral  influences  which  pass 
to  and  regulate  the  discharges  of  the  respiratory  center. 

Effects  of  Vitiated  Air.  Ventilation.  As  the  air  expired  from 
the  lungs  contains  a  large  proportion  of  carbon  dioxide  and  a  minute  amount 
of  organic  matter,  it  is  obvious  that  if  the  same  air  be  breathed  again  and 
again,  the  proportion  of  carbon  dioxide  and  organic  matter  in  it  will  con- 
stantly increase  till  it  becomes  unfit  to  breathe;  long  before  this  point  is 
reached,  however,  uneasy  sensations  occur,  such  as  headache,  languor,  and 
a  sense  of  oppression.  It  is  a  remarkable  fact,  however,  that  the  organism 
after  a  time  adapts  itself  to  a  very  vitiated  atmosphere,  and  that  a  person 
soon  comes  to  breathe,  without  sensible  inconvenience,  an  atmosphere  which, 
when  he  first  enters  it,  feels  intolerable.  Such  an  adaptation,  however,  can 
take  place  only  at  the  expense  of  a  depression  of  all  the  vital  functions,  which 
must  be  injurious  if  long  continued  or  often  repeated.  This  power  of  adapta- 
tion is  well  illustrated  by  an  experiment  of  Claude  Bernard.  If  a  sparrow 
is  placed  under  a  bell-glass  of  such  size  that  it  will  live  for  three  hours,  be  taken 
out  at  the  end  of  the  second  hour  (when  it  could  have  survived  another  hour), 
and  a  fresh  healthy  sparrow  introduced,  the  latter  will  die  at  once. 

It  must  be  evident  that  provision  for  a  constant  and  plentiful  supply  of 
fresh  air,  and  the  removal  of  that  which  is  vitiated,  are  of  greater  importance 
than  the  actual  cubic  space  per  person  of  occupants.  Not  less  than  2,000  cubic 
feet  per  individual  should  be  allowed  in  sleeping  apartments  (barracks,  hos- 
pitals, etc.),  and  with  this  allowance  the  air  can  be  maintained  at  the  proper 
standard  of  purity  only  by  such  a  system  of  ventilation  as  provides  for  the 
supply  of  1,500  to  2,000  cubic  feet  of  fresh  air  per  person  per  hour. 

Fjjects  0}  Breathing  Gases  Other  than  the  Atmosphere.  Asphyxiation  is 
produced  by  the  direct  poisonous  action  of  such  gases  as  carbon  monoxide, 
which  is  contained  to  a  considerable  amount  in  common  coal  gas.  The 
fatal  effects  often  produced  by  this  gas  (as  accidents  from  burning  charcoal 
stoves  in  small,  close  rooms)  are  due  to  its  entering  into  combinations  with 
the  hemoglobin  of  the  blood-corpuscles  and  thus  preventing  the  formation 
of  oxyhemoglobin  because  of  the  more  stable  carbon-monoxide  hemoglobin. 
The  partial  pressure  of  oxygen  in  the  atmosphere  may  be  considerably  in- 
creased without  much  effect  in  displacing  the  carbon  monoxide,  hence  this 
is  rapidly  fatal  when  breathed.  Hydrogen  may  take  the  place  of  nitrogen 
with  no  marked  ill  effect,  if  the  oxygen  is  in  the  usual  proportions.  Sul- 
pha reted  hydrogen  destroys  the  hemoglobin  of  blood  and  thus  produces  oxygen 
starvation.  Nitrous  oxide  acts  directly  on  the  nervous  system  as  a  narcotic, 
and  may  also  form  a  compound  with  hemoglobin.  Certain  gases,  such  as 
carbon  dioxide  in  more  than  a  certain  proportion,  sulphurous  acid  gases,  am- 
monia, and  chlorine,  produce  spasmodic  closure  of  the  glottis  and  prevent 
respiration. 


280  RESPIRATION 

Alteration  in  the  Atmospheric  Pressure.  The  normal  condition  of  breath- 
ing is  that  the  oxygen  of  the  air  breathed  should  be  at  the  pressure  of  20.96 
per  cent  of  the  atmosphere,  that  per  cent  of  760  mm.  of  mercury,  or  159  mm. 
But  it  is  found  that  life  may  be  carried  on  by  gradual  diminution  of  the  oxygen 
pressure  to  considerably  less  than  one-half  of  this,  to  a  partial  pressure  of 
76  mm.  of  oxygen,  i.e.,  the  oxygen  of  one-half  an  atmosphere.  This 
pressure  is  reached  at  an  altitude  above  15,000  feet.*  Any  pressure 
less  than  this  may  begin  to  produce  alterations  in  the  relations  of 
the  gases  in  the  blood,  and  if  an  animal  is  subjected  suddenly  to  a 
marked  decrease  of  barometric  pressure,  and  so  of  oxygen  pressure 
(below  7  percent  of  oxygen),  it  is  thrown  into  convulsions.  It  is  found  that 
the  gases  are  set  free  in  the  blood-vessels,  no  doubt  carbon  dioxide  and  oxygen 
as  well  as  nitrogen,  although  the  latter  is  the  only  one  of  the  three  gases  the 
presence  of  which  has  been  proven  in  the  vessels  in  death  from  this  condition 
of  affairs.  The  other  gases  are  said  to  be  reabsorbed.  Other  derangements 
may  precede  this,  bleeding  from  the  nose,  dyspnea,  and  vascular  incoordina- 
tion, etc.  On  the  other  hand,  the  oxygen  may  be  gradually  increased  to  a  con- 
siderable extent  without  marked  effect,  even  to  the  extent  of  8  or  10  atmos- 
pheres, but  when  the  oxygen  pressure  is  increased  up  to  20  atmospheres  the 
animals  experimented  upon  by  Paul  Bert  died  with  severe  tetanic  convulsions. 

THE  EFFECT  OF  RESPIRATION  ON  THE  CIRCULATION. 

As  the  heart,  the  aorta,  and  pulmonary  vessels  are  situated  in  the  air- 
tight thorax,  they  are  exposed  to  a  certain  alteration  of  pressure  when  the 
capacity  of  the  latter  is  varied  in  respiration.  The  disturbance  of  pressure 
which  occurs  during  inspiration  causes,  first,  a  decrease  in  the  intrathoracic 
cavity,  a  decrease  in  pressure  which  affects  all  the  organs  of  the  thorax — the 
lungs,  the  great  blood-vessels,  the  heart.  The  expansion  of  the  elastic  lungs 
counterbalances  this  change  in  pressure  in  part,  but  it  never  does  so  entirely, 
since  part  of  the  pressure  within  the  lungs  is  expended  in  overcoming  their 
elasticity.  The  amount  thus  used  up  increases  as  the  lungs  become  more  and 
more  stretched,  so  that  the  intrathoracic  pressure  during  inspiration,  as  far 
as  the  heart  and  great  vessels  are  concerned,  never  quite  equals  the  intra- 
pulmonary  pressure,  and  at  the  conclusion  of  inspiration  is  considerably 
less  than  the  atmospheric  pressure.  It  has  been  ascertained  that  the  amount 
of  the  pressure  used  up  in  the  way  above  described  varies  from  5  to  7  mm.  of 
mercury  in  ordinary  inspiration,  to  30  mm.  of  mercury  at  the  end  of  a  deep 
inspiration.  So  it  will  be  understood  that  the  pressure  to  which  the  heart 
and  great  vessels  are  subjected  diminishes  as  inspiration  progresses,  and  at 

*  For  an  interesting  account  of  the  symptoms  produced  by  diminished  atmospheric 
pressure  by  very  high  altitudes,  consult  Whymper's  "Travels  amongst  the  Andes  of  the 
Equator." 


KFFECT     OF     RESPIRATION     OX     THE     CIRCULATION 


281 


its  minimum  is  less  by  from  7  to  30  mm.  than  the  normal  atmospheric  pres- 
sure, 76c  mm.  of  mercury.  It  will  be  understood  from  the  accompanying 
diagram  how  an  increase  in  the  volume  of  the  thorax  will  have  the  effect  of 
pumping  blood  into  the  heart  from  the  veins.  During  inspiration  the  pressure 
outside  the  heart  and  great  vessels  is  diminished,  and  they,  by  virtue  of  their 
elasticity,  have  therefore  a  tendency  to  expand  and  to  diminish  the  intra- 
vascular pressure.  The  diminution  of  pressure  within  the  veins  passing 
to  the  right  auricle  and  within  the  right  auricle  itself,  will  draw  the  blood 
into  the  thorax,  and  so  assist  the  circulation.  This  suction  action  of  the  thorax 
is  the  cause  of  the  slight  negative  pressure  of  the  ventricle  previously  de- 
scribed. The  effect  of  more  blood  in  the  right  auricle  will,  ceteris  paribus, 
increase  the  amount  passing  through  the  right  ventricle,  and  through 
the  lungs  into  the  left  auricle  and  ventricle,  and  thus  into  the  aorta. 
This    all     tends     to    increase    the    blood    pressure.     The    effect    of    the 


Fig.  240. — Diagram  of  an  Apparatus  Illustrating  the  Effect  of  Inspiration  upon  the  it  *art  and 
Great  Vessels  within  the  Thorax.  I,  The  thorax  at  rest;  II,  during  inspiration;  D  represents  the 
diaphragm  when  relaxed;  D' ,  when  contracted  (it  must  be  remembered  that  this  position  is  a  mere 
diagram),  i.e.,  when  the  capacity  of  the  thorax  is  enlarged;  H,  the  heart;  V,  the  veins  entering 
it,  and  .4,  the  aorta;  Rl,  LI,  the  right  and  left  lung;  T,  the  trachea;  M,  mercurial  manometer  in 
connection  with  pleura.  The  increase  in  the  capacity  of  the  box  representing  the  thorax  is  seen  to 
dilate  the  heart  as  well  as  the  lungs,  and  so  to  pump  in  blood  through  V,  whereas  the  valve  pre- 
vents reflux  through  .4 .  The  position  of  the  mercury  in  .1/  shows  also  the  suction  which  is  taking 
place.      (Landois.) 

diminished  pressure  upon  the  pulmonary  vessels  will  also  help  toward  the 
same  end,  an  increased  flow  through  the  lungs,  so  that,  as  far  as  the  mechani- 
cal effects  on  the  heart  and  its  veins  are  concerned,  inspiration  increases 
the  blood  pressure  in  the  arteries.  The  effect  of  inspiration  upon  the  aorta 
and  its  branches  within  the  thorax  would  be,  however,  contrary;  for  as  the 
external  pressure  is  diminished,  the  vessels  would  tend  to  expand,  and  thus 
to  diminish  the  tension  of  the  blood  within  them,  but,  inasmuch  as  the  rela- 
tive variation  in  pressure  on  the  large  arteries  is  slight,  the  diminution  of 
arterial  tension  caused  bv  this  means  will  be  insufficient  to  counteract  the 


282  RESPIRATION 

increase  of  blood  pressure  produced  by  the  effect  of  inspiration  upon  the 
volume  of  discharge  of  the  veins  of  the  chest,  and  the  balance  of  the  whole 
action  would  be  in  favor  of  an  increase  of  blood  pressure  during  the  inspira- 
tory period.  When  a  blood-pressure  tracing  is  taken  at  the  same  time  that 
the  respiratory  movements  are  being  recorded,  it  will  be  found  that,  although, 
speaking  generally,  the  arterial  tension  is  increased  during  inspiration,  the 
maximum  of  arterial  tension  does  not  correspond  with  the  acme  of  inspira- 
tion, figure  241.  In  fact,  at  the  beginning  of  inspiration  the  pressure  con- 
tinues to  fall  for  a  brief  moment,  then  gradually  rises  until  the  end  of 
inspiration,  and  continues  to  do  so  for  a  moment  after  expiration  has  com- 
menced. For  explanation  of  the  influence  of  heart  rate  in  this  variation  of 
blood  pressure,  associated  with  the  respiratory  movement,  see  page  181. 

In  ordinary  expiration  all  this  would  be  reversed,  but  if  the  abdominal 
muscles  are  violently  contracted,  as  in  extraordinary  expiration,  the  same 


Fig.  241. — Comparison  of  Blood-Pressure  Curve  with  Curve  of  Intrathoracic  Pressure.  (To 
be  read  from  left  to  right.)  a  is  the  curve  of  blood  pressure  with  its  respiratory  undulations,  the 
slower  beats  on  the  descent  being  very  marked;  b  is  the  curve  of  intrathoracic  pressure  obtained 
by  connecting  one  limb  of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i  and  expira- 
tion at  e.  The  intrathoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory 
effort,  and  then  slowly  falls  as  the  air  issues  from  the  chest;  at  the  beginning  of  the  inspiratory 
effort  the  fall  becomes  more  rapid.      (M.  Foster.) 

relative  effect  would  be  produced  as  by  inspiration.  The  immediate  effect 
during  inspiration  of  the  diminished  intrathoracic  pressure  upon  the  pul- 
monary vessels  is  to  produce  an  initial  dilatation  of  both  artery  and  veins, 
and  this  delays  for  a  moment  the  passage  of  blood  toward  the  left  side  of  the 
heart,  resulting  in  an  initial  fall  in  the  arterial  pressure,  but  the  fall  of  blood 
pressure  is  immediately  followed  by  a  steady  rise,  since  the  flow  is  increased 
by  the  initial  dilatation  of  the  vessels.  The  converse  is  the  case  with  ex- 
piration. As,  however,  the  pulmonary  veins  are  more  easily  dilatable  than 
the  pulmonary  artery,  their  greater  distensibility  increases  the  flow  of  blood 
as  inspiration  proceeds,  while  during  expiration,  except  at  its  beginning, 
this  property  of  theirs  acts  in  the  opposite  direction,  and  diminishes  the  flow. 
Thus,  at  the  beginning  of  inspiration  the  diminution  of  blood  pressure,  which 


LABORATORY  EXPERIMENTS  283 

commenced  during  expiration,  is  continued,  but  after  a  time  the  diminution 
is  succeeded  by  a  steady  rise.  The  reverse  is  the  case  with  expiration — at 
first  a  rise  and  then  a  fall. 

As  regards  the  effect  of  expiration,  the  capacity  of  the  cheet  is  diminished 
and  the  intrathoracic  pressure  returns  to  the  normal,  which  is  still  slightly 
below  the  atmospheric  pressure.  The  effect  of  this  on  the  veins  is  to  in- 
crease their  extravascular  and  so  their  intravascular  pressure,  and  to  di- 
minish the  flow  of  blood  into  the  left  side  of  the  heart,  and  with  it  the  general 
blood  pressure.  Ordinary  expiration  does  not  produce  a  distinct  obstruction 
to  the  circulation,  as  even  when  the  expiration  is  at  an  end  the  intrathoracic 
pressure  is  less  than  the  extrathoracic.  The  effect  of  violent  expiratory 
efforts,  however,  does  have  a  distinct  action  in  obstructing  the  current  of 
blood  through  the  lungs,  as  seen  in  the  congestion  in  the  exaggerated  con- 
dition of  straining,  this  condition  being  produced  by  pressure  on  the  entire 
group  of  pulmonary  vessels. 

There  are  other  mechanical  factors,  such,  for  example,  as  the  effect  of 
the  abdominal  movements,  both  in  inspiration  and  in  expiration,  upon  the 
arteries  and  veins  within  the  abdomen  and  of  the  lower  extremities,  and 
the  influence  of  the  varying  intrathoracic  pressure  upon  the  pulmonary 
vessels,  both  of  which  ought  to  be  taken  into  consideration.  As  regards 
the  first  of  these,  the  effect  during  inspiration — as  the  cavity  of  the  abdomen 
is  diminished  by  the  descent  of  the  diaphragm — should  be  twofold:  on 
the  one  hand,  blood  would  be  sent  upward  into  the  chest  by  compression 
of  the  vena  cava  inferior;  on  the  other  hand,  the  passage  of  blood  down- 
ward from  the  chest  in  the  abdominal  aorta,  and  upward  in  the  veins  of  the 
lower  extremity,  would  be  to  a  certain  extent  obstructed. 

LABORATORY    EXPERIMENTS    IN    RESPIRATION. 

i.  Respiratory  Rate  in  Man.  Count  your  respirations  for  from 
2  to  4  minutes  while  sitting  quietly,  and  determine  the  average  number  per 
minute.  Repeat  the  counting  after  standing  for  5  minutes,  and  after  brisk 
exercise.  These  determinations  involve  the  element  of  consciousness,  under 
which  condition  it  is  difficult  for  a  person  to  breathe  with  his  normal  rate 
and  depth. 

Make  a  series  of  determinations  of  respiratory  rates  of  persons  who  are 
sitting  quietly  but  unconscious  of  your  determinations.  Count  the  rates 
in  a  number  of  persons  of  different  ages;  where  possible,  take  into  considera- 
tion height,  weight,  etc.  Tabulate  the  results  for  a  comparison  and  for 
future  reference. 

2.  The  Character  of  Respiratory  Movements  in  Man.  A  number 
of  instruments  have  been  devised  for  measuring  human  respiratory  move- 
ment, many  of  which  measure  the  change  in  diameter  of  the  chest  in  respira- 


284 


RKSPTRATION 


tory  movemem.  Adjust  one  of  these,  fur  example  Burdon-Sanderson's 
stethograph,  to  the  thorax,  and  record  the  movement  of  the  receiving  tam- 
bour on  a  smoked-paper  kymograph  which  travels  at  the  rate  of  1  cm.  per 
second.  This  record,  called  a  stethogram,  will  exhibit  the  respiratory  rate, 
the  relative  time  of  the  inspiratory  and  expiratory  phases,  and  the  character 
of  each. 

3.  The  Actual  Change  of  Diameter  in  the  Chest  in  Respiration. 
Use  a  caliper  provided  for  the  purpose  and  measure  the  dorso-ventral  diam- 
eter of  the  chest  at  a  series  of  points  along  the  sternum,  taking  the  reading 


Fig.  242. — Change  in  Diameter  of  the  Body  in  Respiration,  Costal  Type,  a.  Outline  of  the 
body  in  forced  expiration.  In  the  heavy  continuous  line,  b,  the  outer  margin  indicates  the  contour  of 
the  body  in  ordinary  inspiration  and  the  inner  margin  that  of  ordinary  expiration,  c,  Contour 
of  forced  inspiration.      (After  Hutchinson.) 


at  the  height  of  the  inspiratory  phase  and  of  the  expiratory  phase  in  ordi- 
nary respiration.  Repeat  the  measurement  in  forced  respiration.  Map 
the  results  on  millimeter  paper,  as  indicated  in  figure  242. 

Repeat  these  measurements  in  the  transverse  diameter  at  the  first,  fifth, 
and  tenth  ribs. 

Using  the  chest  pantograph,  figure  243,  record  the  outline  of  the  chest 
at  the  level  of  the  middle  of  the  sternum  during  expiration  and  at  the  end 
of  inspiration. 

4.  The  Volume  of  Air  Breathed  by  Man.  Determine  the  average 
volume  of  air  breathed  per  respiration,  using  Hutchinson's  spirometer,  figure 
235,  set  the  instrument  at  the  zero  point,  exhale  into  the  instrument  through 
the  tube,  using  all  possible  care  to  breathe  with  your  normal  rate  and  depth. 
Better  results  will  be  obtained  by  taking  the  average  from  sets  of  ten  consecu- 
tive inspirations  into  the  instrument.     From  the  average  of  the  volume  per 


VITAL     CAPACITIES 


285 


respiration,  and  the  average  number  of  respirations  per  minute,  determined 
in  experiment  1,  calculate  the  amount  of  air  breathed  per  hour  and  per  day. 
5.  Vital  Capacities.  Using  the  spirometer  as  in  the  preceding 
experiment,  set  the  instrument  at  zero  and  exhale  into  it:  a,  Begin  with  the 
fullest  possible  inspiration  and  exhale  the  greatest  possible  amount  of  air 
from  the  lungs.     This  is  known  as  the  vital  capacity. 

b,  Beginning  at  the  end  of  an  ordinary  expiration  exhale  into  the  instru- 
ment the  greatest  possible  amount.     This  is  called  the  reserve  air. 

c,  Following  ordinary  inspiration  exhale  into  the  instrument  until  you 
reach  the  ordinary  state  of  expiration.  This  involves  the  conscious  fixing 
of  two  points  in  the  respiratory  act,  namely,  the  summit  of  inspiration  and 
expiration,  w  hich  are  ordinarily  automatically  adjusted  by  the  body.  The 
error  of  the  determination  is  therefore  great.  It  is  better  to  make  this  measure- 
ment in  sets  of  ten,  as  in  the  preceding  experiment,  and  take  the  average. 


Fig.  243. — The  Chest  Pantograph  for  Recording  the  Outlines  of  the  Chest.  The  fixed  point 
in  the  instrument  is  f;  the  points  a,  b,  x,  y,  are  movable  joints;  when  point  /  is  made  to  trace 
the  outline  of  the  chest,  point  r  will  give  a  corresponding  movement  and  can  be  made  to  trace  this 
movement  on  recording  paper.      (Hall.) 


This  reduces  the  error.  This  quantity  of  air  is  known  as  the  tidal  air.  One 
can  measure  the  tidal  air  and  the  reserve  air  together,  check  them  against 
the  sum  of  the  two,  as  in  a  and  b  separately. 

The  sum  of  the  tidal  and  reserve  air  taken  from  the  vital  air  will  leave 
the  amount  which  one  may  inspire  over  and  above  that  in  the  chest  at  the  end 
of  ordinary  inspiration.  This  is  called  complemental.  The  complemental 
can  be  measured  by  inspiring  the  air  from  the  spirometer,  but  this  is  not 
good  hygiene  where  large  numbers  are  using  the  same  instrument,  unless 
the  instrument  be  thoroughly  cleaned  before  the  inspiration  is  taken. 

6.  The  Respiratory  Pressure  in  Man.  Measure  the  respiratory 
pressure,  the  pressure  of  the  air  in  the  air-passages,  by  means  of  the  mercury 
manometer,   or  by  a  graduated   Marey's  tambour.     Connect   the   piece  of 


^280 


RESPIRATION 


gas  tubing  with  the  proximal  limb  of  the  mercury  manometer  and  provide 
it  with  a  glass  mouthpiece.  Insert  this  mouthpiece  well  back  into  the 
cavity  of  the  mouth,  closing  the  lips  firmly  about  it,  leaving  the  pharyngeal 
muscles  relaxed.  Note  the  variations  in  pressure  at  the  height  of  ordinary 
inspiration  and  expiration,  with  the  nasal  passages  open.  Repeat  with 
forced  inspiration  and  expiration,  close  the  nasal  passages,  and  make  the 
maximal  expiratory  and  inspiratory  effort.  The  manometer  may  be  ad- 
justed to  write  on  the  smoked  paper,  or  one  may  read  the  variations  directly 
from  the  manometer  schedule,  in  which  case  it  facilitates  the  reading  if  one 
clamps  the  rubber  tube  at  the  moment  the  reading  is  desired. 

7.   Demonstration   of    Carbon   Dioxide   in   Expired    Air.      Arrange 
two  llasks,  as  in  figure  244,  filling  each  one-third  full  of  baryta  water,  or 


Fig.  244. — Apparatus  for  Demonstrating  Excess  of  C02  in  Expired  Air. 

lime-water. 


Flasks  filled  with 


lime-water.  Close  the  lips  around  the  mouthpiece  of  the  apparatus,  and 
inhale  and  exhale  the  air  through  it;  close  the  nostrils  if  necessary.  The 
inspired  air  will  come  through  a,  the  expired  air  out  through  b.  The  baryta 
water  in  b  will  quietly  become  clouded  with  a  white  precipitate,  while  that 
in  a  will  remain  clear  or  only  very  slightly  clouded,  showing  the  excess  of 
carbon  dioxide  in  expired  air. 

8.  Quantitative  Determination  of  Carbon  Dioxide  and  Oxygen  in 
Inspired  Air  and  in  Expired  Air,  by  Hempel's  Method.  Inspired 
Air.  Fill  a  gas  buret,  see  figure  236,  with  water  and  close  the  pinch- 
cock.  Fill  it  with  air  taken  outside  the  laboratory.  Measure  the  vol- 
ume of  gas  contained  at  the  ordinary  temperature  and  barometric  pressure 
of  the  laboratory.  Connect  with  a  potash  pipet,  drive  the  air  over  into  the 
bulb  of  the  pipet,  shake  it  up  until  all  the  carbon  dioxide  is  absorbed.  Draw 
the  air  back  into  the  buret  and  measure.  The  amount  of  carbon  dioxide 
in  the  external  air  is  usually  so  small  that  it  is  difficult  to  measure  by  this 
method.  Now  connect  the  buret  with  a  pipet  containing  pyrogallic  acid, 
run  the  air  over  into  the  pyrogallic-acid  bulb  and  shake  up  thoroughly  until 
no  further  excess  is  absorbed,  then  remeasure  the  excess  in  the  buret.  The 
loss  in  volume  is  due  to  the  absorption  of  oxygen;  the  air  remaining  in  the 


RESPIRATORY     MOVEMENTS     IN     THE     MAMMAL 


287 


buret  is  nitrogen.  Compute  the  amount  of  carbon  dioxide,  oxygen,  and 
nitrogen  from  the  results  of  your  test. 

Expired  Air.  Take  a  large  sample  of  expired  air  by  breathing  through 
a  large  tube  into  a  gallon  aspirator  bottle.  This  is  large  enough  to  hold 
six  or  eight  expirations.  Now  fill  the  gas  buret  with  a  sample  of  this  expired 
air  and  analyze  as  before,  first  for  carbon  dioxide,  then  for  oxygen;  com- 
pute the  percentage  of  each  gas,  including  nitrogen.  The  expired  air  will 
usually  be  found  to  have  lost  from  4  to  5  per  cent  of  oxygen  and  have  gained 
a  little  more  than  that  quantity  of  carbon  dioxide. 

From  the  percentages  obtained  in  these  experiments,  and  the  volume 
of  air  breathed  per  unit  of  time,  computed  in  experiment  4  above,  determine 
the  amount  of  carbon  dioxide  exhaled  per  hour  per  kilogram  of  weight  for 
your  own  body.     Compute  also  the  amount  of  oxygen  consumed. 

9.  The  Rate  and  Character  of  the  Respiratory  Movements  in  the 
Mammal,  a,  The  rate  of  respiration  can  be  best  determined  by 
direct  count  per  minute,  an  effort  being  made  to  keep  the  animal  under  as 


Fig.  245. 


-Arrangement  of  Tracheal  Cannula  and  Marey's  Tambour  for  Recording  the  Changes 
in  Intratracheal  Pressure  during  Respiration.      (Langendorff.) 


nearly  normal  conditions  as  possible;  make  the  same  determinations  on  a 
cat,  a  dog,  and  guinea-pig.  b,  The  character  of  the  respiratory  movements 
can  be  recorded  by  one  of  the  various  forms  of  stethograph  adapted  to  the 
size  of  the  animal,  or  by  the  arrangement  shown  in  figure  245.  It  is  usually 
better  to  make  the  determination  with  the  animal  under  the  influence  of  an 
anesthetic. 

10.  The  Determination  of  Carbon  Dioxide  Given  Off  in  the  Mam- 
mal. This  determination  can  be  made  only  by  placing  the  animal 
in  a  respiratory  calorimeter,  and  making  the  following  measurements: 

a.  The  amount  of  air  which  passes  through  the  animal  chamber,  the 
calorimeter. 

b.  The  percentage  of  carbon  dioxide  in  the  air  whicli  is  in  the  chamber. 


288 


INSPIRATION 


c.  The  percentage  of  carbon  dioxide  in  the  air  which  leaves  the  chamber. 

If  the  animal  is  small  enough,  for  example,  the  guinea-pig  or  a  mouse, 
the  absorption  tubes  may  be  constructed  of  proper  size  to  absorb  all  the 
carbon  dioxide  passing  through  the  chamber,  and  the  total  quantity  of  any 
unit  of  time  determined  directly  in  grams.  If  now  the  animal  is  weighed 
at  the  moment  it  is  introduced  into  the  cage,  then  the  amount  of  carbon 
dioxide  per  kilo  weight  can  be  quickly  computed. 

Calorimeters  for  larger  animals  require  a  larger  volume  of  ventilation, 
and  the  usual  procedure  is  to  measure  the  percentage  in  a  sample  as  directed 
above. 

ii.   The  Nervous  Mechanism  of  Respiratory  Movement. 

a.  The  Effect  of  Stimulating  Cutaneous  Nerves.  Use  a  small  dog  or  a 
cat  for  this  experiment;  anesthetize  and  introduce  a  tracheal  tube  with  a 
side  branch  adapted  for  measuring  the  variations  of  pressure  during  respira- 
tion. Connect  the  free  limb  of  the  tracheal  tube  with  an  ether  apparatus 
and  adjust  to  secure  constant  anesthesia.     Connect  the  side  branch  of  the 


on    off 


Tnmr-rT-rrs-nr? 


Fig.  246. — Change  in  Respiration  on  Stimulating  the  Central  End  of  the  Sciatic  Nerve.  The 
rate  is  sharply  increased  and  the  amplitude  more  than  doubled.  The  stimulation  is  between  the 
points  marked  on  and  off,  time  in  seconds.  The  inspiratory  movement  following  the  stimulation 
was  greater  than  the  limit  of  the  recording  tambour. 


tracheal  tube  with  a  Marey's  recording  tambour  of  medium  size  and  supply 
with  a  comparatively  delicate  membrane.  The  amplitude  of  the  move- 
ments of  the  tambour  may  be  regulated  by  a  screw  compress  on  a  connecting 
tube.  Arrange  an  induction  coil  with  platinum  electrodes  in  the  usual 
manner,  figure  318,  for  stimulating,  by  means  of  the  interrupted  current. 
Record  the  results  of  the  experiment  along  with  the  variations  of  blood  pres- 
sure on  a  continuous-paper  kymograph;  the  instrument  should  be  supplied 
with  a  time  signal,  a  stimulating  signal,  etc. 


DEMONSTRATION     OF     APNEA,     DYSPNEA,      VXD     ASPHYXIA  280 

Now  stimulate  the  skin  of  the  abdominal  region,  the  groin,  with  a  com- 
paratively strong  induction  current,  figure  246.  Dissect  out  the  sciatic 
nerve,  cut  it,  stimulate  the  central  end  with  a  mild  to  medium  strength  of 
current.  The  stimulus  should  be  graduated  carefully,  for  there  is  often  such 
a  great  increase  in  respiratory  rate  and  volume  that  the  animal  may  become 
overanesthetized. 

b.  The  Effect  of  Stimulating  the  Vagus  Nerve.  Isolate  and  stimulate 
the  vagus  nerve  with  a  medium  strength  of  stimulus.  The  effect  is  usually 
complete  inhibition  of  respiratory  movements.  By  means  of  graduated 
stimuli  one  may  demonstrate  the  accelerator  effects  from  the  stimulation 
of  the  vagus.  Stimulate  also  the  superior  laryngeal,  and  compare  with  the 
eftects  of  stimulating  the  whole  vagus. 

c.  The  Effect  of  Cutting  the  Vagus  Nerves.  Isolate  both  vagus  nerves 
and  section  them  as  nearly  at  the  same  moment  as  possible.  Be  sure  to 
mark  on  the  tracing  the  exact  moment  at  which  the  nerves  are  cut.  This 
experiment  should  be  performed  with  every  accessory  condition  as  constant 
as  possible,  and  the  animal  should  not  be  disturbed  for  one  or  two  minutes 
so  that  the  effects  of  the  section  will  be  recorded  uncomplicated.  The  re- 
sult is  always  a  marked  deepening  and  slowing  of  the  respiratory  movements. 

d.  The  Effect  of  Stimulating  the  Central  End  of  the  Vagus.  Upon  stimu- 
lating the  central  end  of  the  vagus  after  section,  the  respiration  rate  will  be 
inhibited  as  in  b,  showing  that  the  vagus  nerves  carry  afferent  respiratory 
fibers,  figure  239. 

e.  The  Effect  of  Stimulation  of  the  Phrenic  Nerves.  Isolate  the  right 
phrenic  nerve  at  its  origin  from  the  brachial  plexus  and  stimulate  it  with  a 
medium  strength  of  stimulus.  Upon  stimulating  a  nerve  the  diaphragm 
will  remain  in  contraction  and  the  record  will  show  that  the  thorax  is  in  the 
inspiratory  phase. 

Section  this  nerve  and  note  the  change  in  the  character  of  respiratory 
movements;  make  direct  observations  on  the  diaphragm,  examining  from 
the  abdominal  side. 

12.  Demonstration  of  Apnea,  Dyspnea,  and  Asphyxia.  Produce 
deep  anesthesia,  then  disconnect  the  ether  bottle  and  connect  the  tracheal 
tube  with  a  hand  bellows.  Produce  deep  and  forced  artificial  respiration  for 
twenty  to  thirty  seconds.  Stop  the  artificial  respiration;  the  animal  will  re- 
main quiet  without  any  effort  at  breathing.  This  is  the  condition  of  apnea. 
Allow  the  animal  to  recover  its  normal  respiration  rate  and  again  produce 
deep  anesthesia.  Now  clamp  off  the  tracheal  tube  so  that  the  animal  can  no 
longer  receive  air  and  leave  it  so  until  death.  As  the  blood  becomes  more 
and  more  venous  there  will  first  be  a  marked  increase  in  the  respiration  rate 
and  depth.  This  is  known  as  hyper pnea.  This  stage  is  followed  by  one 
of  increasing  respiratory  amplitude  in  which  the  accessory  respiratory  mus- 
cles not  previously  active  are  brought  into  forcible  contractions,  both  inspira- 
19 


290  RESPIRATION 

tory  and  expiratory  phases  are  now  forced,  dyspnea.  The  movements'  con- 
tinue to  increase,  and  the  muscles  of  the  neck,  larynx,  mouth,  and  nostrils 
now  take  part.  There  is  rather  a  sudden  decrease  in  the  respiratory  move- 
ments, an  extension  of  the  limbs,  and  gasping  movements  of  the  mouth,  after 
which  the  animal  remains  quiet,  death  being  produced  by  asphyxia. 

13.  Respiratory  Interchange,  Calorimetry.  The  experiments  are 
conducted  in  such  a  manner  that  comparative  analyses  may  be  made  between 
the  air  inspired  and  that  expired.  Generally  an  animal  is  placed  in  a  cham- 
ber, called  the  respiratory  chamber,  which  is  then  closed  except  for  two 
openings,  one  for  the  entrance  of  the  inspired  air,  the  other  for  the  escape 
of  expired  air.  Some  form  of  pump  is  used  for  renewing  the  air  in  the 
chamber.  Both  the  inspired  and  expired  air  is  made  to  pass  through  agents 
which  will  absorb  the  contained  carbon  dioxide,  such  as  baryta  water  or  soda 
lime,  and  in  turn  through  agents  which  will  absorb  the  watery  vapor.  When 
the  experiment  is  completed  the  differences  between  the  two  are  determined. 
The  difference  in  oxygen  has  to  be  calculated,  and  is  open  to  error. 
The  famous  respiratory  chamber  of  Pettenkofer  is  large  enough  to  per- 
form such  experiments  on  man,  and  is  of  very  elaborate  construction. 
But  the  most  perfect  apparatus  assembled  for  this  purpose  is  the  respira- 
tion calorimeter  of  Atwater  constructed  for  man,  and  the  respiration  ap- 
paratus of  Armsby  for  cattle. 


CHAPTER  VII 

SECRETION  IN  GENERAL 

All  tissues  of  the  body  produce  certain  chemical  changes  as  a  result  of 
their  protoplasmic  activity.  But  in  certain  cells  chemical  elaborations  have 
come  to  be  the  chief  function,  the  cells  have  been  differentiated  in  that  direc- 
tion, and  the  name  secreting  tissue  or  gland  tissue  is  applied.  The  end  result 
of  metabolism  in  gland  tissue  is  the  extrusion  on  the  free  borders  of  the  cells 
of  the  products  of  their  metabolism.  The  products  are  known  as  secretions 
and  the  process  itself  is  the  act  of  secretion.  Certain  secretions  which  are 
in  the  nature  of  waste  products  to  the  body  as  a  whole,  such  as  urine  in  the 
kidney,  are  often  called  excretions,  but  the  use  of  the  term  should  not  be  allowed 
to  confuse  the  general  similarity  of  this  to  other  secretions  as  regards  the 
physiological  changes  involved  in  its  production. 

Most  secretions  accomplish  some  definite  office  in  the  economy  of  the 
body.  Those  that  are  discharged  on  some  free  mucous  surface,  as  the  saliva, 
gastric  juice,  tears,  etc.,  are  called  external,  or  true  secretions,  or  merely  secre- 
tions. Substances  that  are  discharged  back  into  the  blood  stream  later  to 
influence  the  metabolism  of  tissues  other  than  the  ones  which  produced  them, 
are  called  internal  secretions. 

Gland  cells,  like  other  tissues,  draw  their  nourishment  from  the  blood 
and  lymph.  The  product  or  secretion  of  gland  cells  may,  in  fact  usually 
does,  contain  some  of  the  substances  found  in  the  blood,  but  there  are  also 
present  new  materials  elaborated  by  the  cells,  and  even  where  the  same  sub- 
stance exists  both  in  the  secretion  and  in  the  blood  and  lymph  it  can  make 
its  appearance  in  the  secretion  only  under  the  control  of  the  protoplasm  of 
the  gland  cells.  The  saliva  secreted  by  the  salivary  cells,  for  example,  con- 
sists of  about  98  to  99  per  cent  water  containing  in  solution  small  quantities 
of  certain  salts,  also  found  in  the  lymph,  and  a  small  percentage  of  the  en- 
zyme, ptyalin.  This  enzyme  is  peculiar  to  the  salivary  secretion  and  is  manu- 
factured by  the  salivary-cell  protoplasm.  As  is  well  known,  it  acts  vigorously 
in  extreme  dilution,  hence  the  high  per  cent  of  water  in  the  secretion.  The 
passage  of  water  from  a  solution  as  concentrated  as  blood  plasma  to  a  solu- 
tion as  dilute  as  saliva  requires  a  high  amount  of  osmotic  energy,  an  amount 
that  can  be  supplied  only  from  the  chemical  energy  liberated  by  the  cell  in 
its  protoplasmic  activity.  After  the  removal  of  the  special  organ  by  which 
each  secretion  is  manufactured,  the  secretion  is  no  longer  formed.     Cases 

291 


292  SECRETION     TN    GENERAL 

sometimes  occur  in  which  the  secretion  continues  to  be  formed  by  the  natural 
organ,  but,  not  being  able  to  escape  toward  the  exterior,  on  account  of  some 
obstruction,  is  reabsorbed  and  accumulates  in  the  blood.  It  may  be  dis- 
charged from  the  body  in  other  ways;  but  these  are  not  instances  of  true 
vicarious  secretions,  and  must  not  be  so  regarded. 

Organs  and  Tissues  of  Secretion.  The  principal  secreting  organs 
are  the  following:  i,  The  serous  and  synovial  membranes;  2, The  mucous  mem- 
branes with  their  special  glands,  e.g.,  the  buccal,  gastric,  and  intestinal  glands; 
3,  The  salivary  glands  and  pancreas;  4,  The  liver;  5,  The  mammary  glands; 
6,  The  lachrymal  glands;  7,  The  kidney  and  skin;  and  8,  the  testes  and 
ovaries. 

The  special  structure  and  functions  of  the  secreting  organs  will  be  given 
in  greater  detail  in  the  chapters  which  immediately  follow.  The  general 
types  of  structure  and  general  conditions  that  influence  the  functions  are 
introduced  at  this  point. 

Structural  Types  of  Secreting  Organs.  Serous  and  Synovial  Type. 
The  serous  membranes  form  closed  sacs  lining  visceral  cavities  like  the 
abdominal,  pericardial,  or  pleural  cavities.  The  organs  are,  as  it  were,  pushed 
into  this  sac  and  carry  before  them  an  investment  of  membrane.  The  serous 
membranes  consist  of  a  single  layer  of  flattened  polygonal  cells  resting  on  a 
supporting  membrane  of  connective  tissue,  supporting  a  ramification  of  blood- 
vessels, lymphatics,  and  nerves. 

In  some  instances,  i.e.,  synovia]  membranes,  the  secreting  layer  is  in- 
creased by  finger-like  elevations.  This  type  of  secreting  organ  producer 
ordinarily  only  enough  secretion  to  keep  the  surface  moist. 

The  Mucous  Type.  The  mucous  tracts,  and  different  portions  of  e  xh 
of  them,  present  certain  structural  peculiarities,  adapted  to  the  functions 
which  each  part  has  to  discharge;  yet  in  some  essential  characters  the  mucous 
membrane  is  the  same,  from  whatever  part  it  is  obtained.  In  all  the  princi- 
pal and  larger  parts  of  the  several  tracts  it  presents  an  external  layer  of  epithe- 
lium, situated  upon  a  basement  membrane,  and  beneath  this  a  stratum  of 
vascular  tissue  of  variable  thickness,  containing  lymphatic  vessels  and  nerves. 
The  vascular  stratum,  together  with  the  basement  membrane  and  epithelium, 
in  certain  cases  is  elevated  into  minute  papilla;  and  villi,  in  others  depressed 
into  involutions  in  the  form  of  glands.  But  in  the  invaginations  of  the  secreting 
membrane  of  gland  cells,  the  supporting  basement  membrane  and  the  network  of 
capillaries  are  still  retained  in  their  relative  position.  With  increasing  complexity 
of  involution  the  simple  mucous  membrane  becomes  packed  away  in  an  ap- 
parently solid  mass.  The  equivalent  of  a  large  amount  of  secreting  surface 
is  thus  condensed  into  a  small  space.  In  the  process  of  invagination  some 
differentiation  occurs  in  that  certain  of  the  gland  tubes  become  conducting 
and  have  their  secretory  activity  somewhat  reduced.  But  there  is  no  distinc- 
tion that  can  be  drawn  between  simple  mucous  membranes  and  gland  cells. 


SECRETING     GLANDS 


293 


Secreting  Glands.  The  secreting  glands  present,  amid  manifold 
diversities  of  form  and  composition,  a  general  plan  of  structure;  but  all  are 
constructed  with  particular  regard  to  the  arrangement  of  the  cells  which  has 
just  been  described. 

Secreting  glands  are  classified  according  to  certain  structural  types,  as: 
i.  The  simple  tubular  gland,  A,  figure  247,  examples  of  which  are  furnished 
by  the  follicles  of  Lieberkiihn,  and  the  tubular  peptic  glands  of  the  stomach. 


Fig.  247. — Plans  of  Extension  of  Secreting  Membrane  by  Inversion  or  Recession  in  theFormsof 
Cavities.  A,  bimple  glands,  viz..  g,  straight  tube;  h,  sac;  *,  coiled  tube.  B,  Multilocular  crypts: 
k,  of  tubular  form;  I,  saccular.  C,  Racemose  or  saccular  compound  gland'  m,  entire  gland,  show- 
ing branched  duct  and  lobular  structure;  n,  a  lobule,  detached  with  o,  branch  of  duct  proceeding 
from  it.      D,  Compound  tubular  gland.      (Sharpey.) 

They  are  simple  tubes  of  mucous  membrane,  the  walls  of  which  are  lined  with 
secreting  cells  arranged  as  an  epithelium.  To  the  same  class  may  be  referred 
the  elongated  and  tortuous  sudoriferous  glands. 

2.  The  compound  tubular  glands,  D,  figure  247,  form  another  division. 
These  consist  of  main  gland  tubes,  which  divide  and  subdivide.  Each  gland 
may  be  made  up  of  the  subdivisions  of  one  or  more  main  tubes.    The  ulti- 


294  SECRETION    IN    GENERAL 

mate  subdivisions  of  the  tubes  are  sometimes  highly  convoluted.  They  are 
formed  of  epithelium  of  various  forms,  supported  by  a  basement  membrane.  , 
The  larger  tubes  may  have  an  outside  coating  of  fibrous  areolar  or  muscular 
tissue.  The  salivary  glands,  pancreas.  Brunner's  glands,  kidney,  testes,  with 
the  lachrymal  and  mammary  glands,  are  examples  of  this  type,  but  presf  nt 
more  or  less  marked  variations  among  themselves. 

3.  The  racemose  glands,  in  which  a  number  of  vesicles  or  acini  are  arranged 
in  groups  of  lobules,  C,  figure  247.  The  Meibomian  follicles  are  examples 
of  this  kind  of  gland.  There  seem  to  be  glands  of  mixed  character,  com- 
bining some  of  the  characters  of  the  tubular  with  others  of  the  racemose  type; 
these  are  called  tubulo-racemose  or  tubulo-acinous  glands.  The  acini  aie 
formed  by  a  kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus  combine 
to  form  one  large  cavity  with  recesses  lined  or  filled  with  secreting  cells.  The 
smallest  branches  of  the  gland-ducts  sometimes  open  into  the  centers  of  these 
cavities;  sometimes  the  acini  are  clustered  round  the  extremities,  or  by  the  sides 
of  the  ducts;  but,  whatever  secondary  arrangement  there  may  be,  all  have  the 
same  essential  character  of  rounded  groups  of  vesicles  containing  gland-cells, 
and  opening  by  a  common  central  cavity  into  minute  ducts,  which  in  the 
large  glands  converge  and  unite  to  form  larger  and  larger  branches,  and  at 
length  one  common  trunk  which  opens  on  a  free  surface. 

The  Process  of  Secretion.  The  process  of  secretion  is  dependent 
upon  the  activity  of  the  secreting  cells.  In  the  case  of  the  water  and  salts  the 
physical  processes  of  filtration  and  diffusion  may  play  a  part. 

The  chemical  processes  constitute  the  process  of  secretion  properly  so  called, 
as  distinguished  from  mere  transudation  spoken  of  above.  In  the  process  of 
secretion,  various  materials  which  do  not  exist  as  such  in  the  blood  are  manu- 
factured by  the  agency  of  the  gland-cells,  using  as  a  nutrient  fluid  the  blood, 
or,  to  speak  more  accurately,  the  lymph  which  fills  the  interstices  of  the  gland 
textures. 

Evidences  in  favor  of  this  view  are:  1.  That  gland  cells  are  constituents 
of  all  glands,  however  diverse  their  outer  forms  and  other  characters,  and 
they  are  placed  in  all  glands  on  the  surfaces  or  in  the  cavity  whence  the  secre- 
tion is  poured.  2.  That  certain  materials  of  secretions  are  visible  with  the 
microscope  in  the  gland  cells  before  they  are  discharged.  Thus,  granules 
probably  representing  the  precursors  of  the  ferments  of  the  pancreas  may 
be  discerned  in  the  cells  of  that  gland.  Granules  of  uric  acid  are  found  in 
the  cells  of  the  kidneys  of  birds  and  fish,  and  fatty  particles,  like  those  of  milk, 
in  the  cells  of  the  mammary  gland. 

Certain  secreting  cells,  like  the  cells  of  the  sebaceous  glands,  appear  to 
develop,  grow7,  and  attain  their  individual  perfection  by  appropriating  nutri- 
ment from  the  fluid  exuded  by  adjacent  blood- vessels  and  building  it  up  so 
that  it  shall  form  part  of  their  own  substance.  In  this  perfected  state  the  cells 
subsist  for  some  brief  time  and  dun  appear  to  dissolve,  wholly  or  in  part,  and 


CIRCUMSTANCES     INFLUENCING     SECRETION  295 

yield  their  contents  to  the  peculiar  material  of  the  secretion.  The  changes 
which  have  been  noticed  from  actual  experiment  in  the  cells  of  the  salivary 
glands,  pancreas,  and  peptic  glands  will  be  described  more  fully  in  the  chapter 
on  Digestion. 

Discharge  of  secretions  from  the  glands  may  either  take  place  as  soon  as 
formed,  or  the  secretion  may  be  long  retained  within  the  gland  or  its  ducts. 
The  former  is  the  case  with  the  sweat  glands.  But  the  secretions  of  those 
glands  whose  activity  of  function  is  periodical  are  usually  retained  in  the  cells 
in  an  undeveloped  form  during  the  period  of  the  gland's  inaction. 

When  discharged  into  the  ducts,  the  further  course  of  secretions  is  affected: 
(x)  partly  by  the  pressure  from  behind;  the  fresh  quantities  of  secretion  pro- 
pelling those  that  were  formed  before.  In  the  larger  ducts,  its  propulsion  is 
(2)  assisted  by  the  contraction  of  their  walls.  All  the  larger  ducts,  such  as 
the  ureter  and  common  bile-duct,  possess  in  their  coats  plain  muscular  fibers; 
they  contract  when  irritated,  and  sometimes  manifest  peristaltic  movements. 
Rhythmic  contractions  in  the  pancreatic  and  bile  ducts  have  been  observed, 
and  also  in  the  ureters  and  vasa  deferentia.  It  is  probable  that  the  contractile 
power  extends  along  the  ducts  to  a  considerable  distance  within  the  substance 
of  the  glands  whose  secretions  can  be  rapidly  expelled.  Saliva  and  milk,  for 
instance,  are  sometimes  ejected  with  much  force. 

Circumstances  Influencing  Secretion.  The  principal  conditions 
which  influence  secretion -are  variations  in  the  quantity  of  blood,  and  varia- 
tions in  nerve  impulses  passing  to  the  gland  cells  over  secretory  nerve  fibers. 

An  increase  in  the  quantity  of  blood  traversing  a  gland,  as  in  nearly  all 
the  instances  before  quoted,  coincides  generally  with  an  augmentation  of  its 
secretion.  Thus  the  mucous  membrane  of  the  stomach  becomes  florid  when, 
on  the  introduction  of  food,  its  glands  begin  to  secrete.  The  mammary  gland 
becomes  much  more  vascular  during  lactation.  All  circumstances  which  give 
rise  to  an  increase  in  the  quantity  of  material  secreted  by  an  organ  produce, 
coincidently,  an  increased  supply  of  blood.  But  we  shall  see  that  a  discharge 
of  saliva  may  occur  under  extraordinary  circumstances  without  increase  of 
blood-supply,  and  so  it  may  be  inferred  that  this  condition  of  increased  blood- 
supply  is  not  absolutely  essential  to  the  immediate  formation  of  secretion, 
but  that  it  favors  the  prolonged  activity  of  glands. 

Influence  of  the  Nervous  System  on  Secretion.  The  process  of 
secretion  is  largely  regulated  through  the  nervous  system.  The  exact  mode 
in  which  the  influence  is  exhibited  must  still  be  regarded  as  somewhat  obscure. 
In  part,  it  exerts  its  influence  by  increasing  or  diminishing  the  quantity  of 
blood  supplied  to  the  secreting  gland,  in  virtue  of  the  power  which  it  exercises 
over  the  contractility  of  the  smaller  blood-vessels.  It  also  has  a  more  direct 
influence,  as  is  described  at  length  in  the  case  of  the  submaxillary  gland,  upon 
the  secreting  cells  themselves.  This  may  be  called  trophic  influence.  Its 
influence  over  secretion,  as  well  as  over  other  functions  of  the  body,  may  be 


296  SECRETION     IX     GENERAL 

excited  by  causes  acting  directly  upon  the  nervous  centers,  upon  the  nerves 
going  to  the  secreting  organ,  or  upon  the  nerves  of  other  parts.  In  the  latter 
case  a  reflex  action  is  produced:  thus  the  impression  produced  upon  the  sen- 
sory nerves  by  the  contact  of  food  in  the  mouth  leads  to  afferent  nerve  impulses 
to  the  secretory  center  in  the  central  nervous  system  which  is  reflected  by  the 
nerves  supplying  the  salivary  glands,  and  produces,  through  these,  a  more 
abundant  secretion  of  the  saliva. 

Through  the  nerves,  various  conditions  of  the  brain  also  influence  the 
secretions.  Thus,  the  thought  of  food  may  be  sufficient  to  excite  an  abundant 
flow  of  saliva.  And,  probably,  it  is  the  mental  state  which  excites  the  abun- 
dant secretion  of  urine  in  hysterical  paroxysms,  as  well  as  the  perspirations, 
and  occasionally  diarrhea,  which  ensue  under  the  influence  of  terror,  and  the 
tears  excited  by  sorrow  or  excess  of  joy.  The  quality  of  a  secretion  may  also 
be  affected  by  mental  conditions,  as  in  the  cases  in  which,  through  grief  or 
passion,  the  secretion  of  milk  is  altered,  and  is  sometimes  so  changed  as  to 
produce  irritation  in  the  alimentary  canal  of  the  child. 


CHAPTER  VIII 

FOOD  AND  DIGESTION 

The  term  digestion  includes  those  changes  taking  place  in  the  body  which 
bring  the  materials  of  the  food  into  such  condition  that  they  may  be  taken  up 
by  the  blood  and  lymphatic  vessels  and  thus  rendered  available  for  the  metab- 
olism of  the  tissues.  In  the  process  the  foods  are  rendered  more  soluble 
and  more  diffusible.  Certain  bodies  which  are  already  soluble  and  diffusible 
are  converted  into  forms  which  are  more  available  for  the  tissues;  as  an  ex- 
ample cane-sugar,  although  both  soluble  and  diffusible,  cannot  be  readily 
used  by  the  body  until  it  is  converted  from  a  disaccharide  to  a  monosaccharide. 
In  fact  few  of  the  food  materials  are  fit  for  immediate  use  when  taken  into 
the  body  and  are  therefore  practically  useless  until  digested. 

FOOD    AND    FOOD    PRINCIPLES. 

We  have  been  accustomed  to  classify  foods  into  certain  main  groups,  chieflv 
according  to  their  chemical  character,  as  follows: 

Proteids.  Such  as  albumin,  myosin,  gluten,  casein,  etc.;  gluco- 
proteid,  nucleoproteid,  etc.;  gelatin,  elastin,  etc.  These  furnish  nitrogen  in 
available  form. 

Carbohydrates.     Such  as  starch,  dextrose,  cane-sugar,  etc. 

Fats,     Such  as  olein. 

Minerals.      The  various  salines  found  in  animal  and  vegetable  food. 

Water. 

The  classes  of  foods  just  enumerated  usually  exist  in  mixtures  rather  than 
in  simple  forms,  as,  for  example,  a  beef  roast  contains  a  representative  of  each 
of  the  five  classes  enumerated,  though  it  is  composed  chiefly  of  proteids  and 
fats.  The  human  body  is  capable  of  using  materials  of  a  great  variety  of 
forms,  but  most  of  these  have  the  foods  mixed  in  such  a  way  as  to  give  repre- 
sentatives of  each  of  the  classes  above  in  certain  general  proportions. 

Nitrogenous  Foods.  The  Flesh  oj  Animals,  e.g.,  beef,  veal,  mutton, 
pork,  bacon,  ham,  chicken,  eggs,  milk,  etc.,  are  typical  nitrogenous  foods. 

Of  these,  beef  and  eggs  are  richest  in  nitrogenous  matters,  containing  about 
20  per  cent.  Mutton  contains  about  iS  per  cent,  veal  16.5,  and  pork  10. 
Beef  is  firmer,  more  satisfying,  and  is  supposed  to  be  more  strengthening  than 

297 


208 


F(  )0  D     AND     DIG  ESTION 


mutton,  whereas  the  latter  is  more  digestible.  The  flesh  of  young  animals,  such 
as  lamb  and  veal,  is  less  digestible  and  less  nutritious.  Fork  contains  a  large 
amount  of  fat  and  is,  therefore,  comparatively  indigestible. 

Percentage  Composition  and  Fuel  Value  per  Pound  of  Some  Common  Food  Stuffs. 
(Atwater  and  Bryant.) 


Meat  (Beef,  round) 

Meat  (Fork  loin) 

Fish  (King  salmon) 

Eggs 

Milk  (Cow's) 

Milk  (Human) 

Cheese  (American) 

Butter 

Bread  (White) 

Bread  (Corn) 

Rice 

Oatmeal 

Beans  (Dry) 

Potatoes  (White) 

Potatoes  (Sweet) 

Fruit  (Strawberries) 

Watermelon  (Edible  portion) 


73-6 

52. O 
63.6 

73-7 
87.0 
89.7 
31.6 
1 1 .0 
33-2 
38.9 
12.3 

7-3 
12.6 

78-3 
69.0 
90.4 
92.4 


22.6 

16.6 

17.8 

13-4 

3-3 

2.0 

28.8 

1.0 

10.9 

7-9 
8.0 
16. 1 
22.5 
2.2 
r.8 
1 .0 
0.4 


So 


30.1 
17.8 

io-5 
4.0 

3-1 
35-9 
85.0 

i-3 
4-7 
o-3 
7.2 
1.8 
0.1 
0.7 
0.6 


nix:  « 


5-0 
6.0 

0-3 


53-6 
46.3 
79.0 

67-5 
59-6 
18.4 

27.4 
7-4 
6-7 


1 .0 
0.7 
0.2 
3-4 
3-o 
1 .0 
2.2 
0.4 
1.9 

3-5 
1 .0 
1.2 
0.6 
0-3 


^  a 

-r>0 


540 

I,58o 

1,080 

720 

325 

2,055 
3,605 

1,255 

1,205 

1,63c 

I,86o 

1,605 

385 

570 

180 

140 


Meat  contains:  (1)  Nitrogenous  bodies;  chiefly  myosin,  and  one  or  more 
globulins,  serum  albumin,  gelatin  (from  the  interstitial  fibrous  connective 
tissue),  elastin  (from  the  elastic  tissue),  as  well  as  hemoglobin.  (2)  Fats, 
including  lecithin  and  cholesterin.  (3)  Extractives,  some  of  which  are  agreeable 
to  the  palate,  and  others  weakly  stimulating.  Besides,  there  are  sarcoladic 
and  inositic  acids,  taurin,  xanthin,  and  others.  (4)  Salts,  chiefly  of  potassium, 
calcium,  and  magnesium.  (5)  Water,  the  amount  of  which  varies  from  15 
per  cent  in  dried  bacon  to  39  in  pork,  51  to  53  in  fat  beef  and  mutton,  and  72 
per  cent  in  lean  beef  and  mutton.  (6)  A  certain  amount  of  carbohydrate 
material  is  found  in  the  meat  of  some  animals,  in  the  form  of  inosite,  dextrin, 
grape  sugar,  and  glycogen. 

Table  of  Percentage  Composition  of  Beef,  Mutton,  Pork,  and  Veal.  (Letheby.) 

Water.  Proteid.  Fats.  Salts. 

Bee)— Lean 72  19.3  3.6  5.1 

"      Fat 51  14-8  29.8  4.4 

Mutton — Lean 72  18.3  4.9  4.8 

Fat 53  12.4  3T-T  3-5 

Veal 63  16.5  15.8  4.7 

Pork— Fat 39  9-8  48.9  2.3 


NITROGENOUS     FOOD  299 

Table  of  Percentage  Composition  of  Poultry  and  Fish.     (Letheby.) 

Water.  Proteid.  Fats.  Salts. 

Poultry 74  21.              3.8         1.2 

White  Fish 78  18. 1            2.9         1. 

Salmon 77  16. 1            5.5          1.4 

Eels  (very  rich  in  fat) 75  9.9  13-8         1.3 

Oysters 75-74  11.72         2.42      2.73 

The  flesh  of  nearly  all  animals  has  been  occasionally  eaten,  and  we  may 
presume  that  except  for  difference  of  flavor,  etc.,  the  average  composition 
is  nearly  the  same  in  every  case. 

Milk.  Milk  is  the  entire  food  of  young  animals,  and  contains  all  the 
elements  of  a  typical  diet.  Albuminous  substances  are  represented  in  the 
form  of  caseinogen,  and  serum  or  lact  albumin;  fats  in  the  cream;  carbo- 
hydrates in  the  form  of  lactose  or  milk-sugar;  salts,  chiefly  as  calcium  phos- 
phate; and  water.  From  milk  we  obtain  a  number  of  food  preparations  such 
as  cheese  rich  in  proteid  and  fat,  butter  and  cream,  buttermilk  rich  in  proteids 
and  peculiarly  well  adapted  for  invalid  diet,  and  whey  which  contains  all 
the  sugar  salts  and  the  albumin. 

Table  of  Composition  of   Milk,  Buttermilk,  Cream,    and  Cheese.     (Letheby 

and  Payen.) 

Nitrogenous 

Matters.  Fats.  Lactose.  Salts.  Water. 

Mttk{Co-w) 4.1  3.9  5.2           .8  86 

Buttermilk 4.1  .7  6.4            .8  88 

Cream 4.1  26.7  2.8  1.8  66 

Cheese — Skim 44-8  6.3  ...  4.9  44 

Cheese — Cheddar 28.4  31-!          4-5  36 

Eggs.  The  yolk  and  albumin  of  eggs  of  oviparous  animals  bear  the 
same  relation  as  food  for  the  embryos  that  milk  bears  to  the  young  of  mam- 
malia, and  afford  another  example  of  the  natural  admixture  of  the  various 
alimentary  principles.  The  proteids  of  eggs  are  egg  albumin  and  globulin, 
of  which  the  vitellin  of  the  yolk  is  most  important;  nuclein  in  combination 
with  iron  is  also  found.  In  addition  to  the  three  common  fats  there  is  a  yellow 
fatty  pigment,  lutein  (lipochrome),  lecithin,  and  cholesterin,  a  small  quantity 
of  grape-sugar,  and  inorganic  salts,  chiefly  potassium  chloride  and  phosphates. 

Table  of  the  Percentage  Composition  of  Fowls'  Eggs. 

Nitrogenous 

Substances.  Fats.  Salts.     Water. 

White 20.4  ...  1.6         78 

Yolk 16.  30.7        1.3         52 

Legumes  are  used  by  vegetarians  as  the  principal  source  of  the  nitrogen  of 
the  food.  Those  chiefly  used  are  peas,  beans,  lentils,  etc.;  they  contain  a 
nitrogenous  substance  called  legumin,  allied  to  albumin.     Legumes  contain 


300  FOOD     AND     DIGESTION 

about  25.30  per  cent  of  this  nitrogenous  body,  and  twice  as  much  nitrogen  as 
wheat.     Nuts  also  form  a  very  nutritious  article  of  diet. 

Carbohydrate  Foods.  Bread,  made  from  the  ground  grain  ob- 
tained from  various  so-called  cereals,  viz.,  wheat,  rye,  maize,  barley,  rice, 
oats,  etc.,  is  the  direct  form  in  which  the  carbo-hydrate  is  supplied  in  an 
ordinary  diet.  It  contains  starch,  dextrin,  and  a  little  sugar.  It  also  contains 
gluten,  composed  of  vegetable  proteids,  and  a  small  amount  of  fat. 

Table  of  Percentage  Composition  of  Bread  and  Flour. 

Nitrogenous  Carbo- 

matters.  hydrates.  Fats.  Salts.  Water. 

Bread 8.1                  51.  1.6  2.3  37 

Flour 10.8                  70-85  2  1.7  15 

Various  articles  besides  bread  are  made  from  flour,  e.g.,  spaghetti,  maca- 
roni, etc.  Dextrin  and  a  small  amount  of  dextrose  are  present  in  bread, 
particularly  in  the  crust. 

Vegetables,  especially  potatoes.  They  contain  starch  and  sugar.  In  cab- 
bage, turnips,  etc.,  the  salts  of  potassium  are  abundant. 

Fruits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric,  and  others. 

Sugar,  chiefly  saccharose,  used  pure  or  in  various  sweetmeats. 

Oils  and  Fats.  The  substances  supplying  the  oils  and  fats  of  the 
food  are  chiefly  butter,  bacon  and  lard,  suet  (beef  and  mutton  fat),  and  vegetable 
oils.  These  contain  the  fats  olein,  stearin,  and  palmitin.  Butter  contains 
others  in  addition,  while  vegetable  oils,  as  a  rule,  contain  no  stearin. 

Mineral  or  Inorganic  Foods.  The  salts  oj  the  food.  Nearly  all 
the  substances  in  the  preceding  classes  contain  a  greater  or  less  amount  of 
the  salts  required  in  food.  Green  vegetables  and  fruit  contain  certain  salts, 
chiefly  potassium.  Sodium  chloride  is  an  essential  food;  it  is  contained  in 
nearly  all  solids,  but  so  much  is  required  that  it  has  also  to  be  taken  as  a 
condiment.  Potassium  salts  are  found  in  muscle,  nerve,  and  in  meats  gener- 
ally, and  in  potatoes.  Calcium  salts  are  contained  in  eggs,  blood  of  meat, 
wheat,  and  vegetables.  Iron  is  contained  in  hemoglobin,  in  milk,  eggs,  and 
vegetables. 

Liquid  Foods.  Water  is  essential  to  life,  and  from  two  to  two  and 
a  half  pints  a  day  must  be  consumed  in  addition  to  that  taken  mixed  with 
solid  food.  Of  the  non-alcoholic  substances  which  may  be  added  to  it  for 
flavoring  purposes,  such  as  tea,  coffee,  cocoa,  etc.,  the  last  can  alone  be  con- 
sidered to  have  a  certain  food  value,  as  it  contains  fats,  albuminous  material, 
and  starch,  the  other  constituents  of  such  substances  being  a  volatile  oil,  an 
alkaloid  caffeine,  and  tannic  acid.  The  food  value  of  alcoholic  beverages, 
which  has  long  been  a  subject  of  controversy,  as  now  generally  agreed  is  but 
slight.  Beer,  wines,  and  spirits  contain  ethyl  alcohol,  the  amount  varying 
from  1.5  to  4.5  per  cent  in  beer  to  60  to  80  per  cent  in  spirits. 


THE     PROCESS    OF    DIGESTION  SOI 

The  Effect  of  Cooking  on  Foods.  Jn  general  terms  cooking  may 
be  said  to  render  food  more  easily  digestible,  both  directly  and  indirectly, 
through  increased  palatability.  Subjecting  food  to  high  degrees  of  heat  also 
serves  to  kill  parasites,  such  as  trichinae  and  the  various  tapeworms,  which 
may  be  present  and  alive  in  raw  meats.  In  the  case  of'meats  various  methods 
of  cooking  are  employed.  In  roasting,  the  meat  in  bulk  is  subjected  to  a 
high  temperature  in  an  oven  for  a  short  time,  followed  by  a  somewhat  lower 
temperature  until  the  cooking  is  completed,  which  causes  a  coagulation  of 
the  outer  layers  of  albumin  so  that  the  juices  of  the  meat  are  retained.  In 
boiling,  the  meat  is  first  immersed  in  boiling  water  for  a  time  and  then  the 
cooking  continues  at  a  lower  temperature.  If  a  broth  is  to  be  made,  the  ex- 
tractives may  be  obtained  by  heating  the  meat  in  water  for  a  long  period  at 
a  temperature  below  the  coagulation  point  of  albumin.  Such  a  broth  con- 
tains the  flavoring  and  the  stimulating  extracts  of  the  meat,  but  is  of  only 
slight  nutritive  value.  For  small  pieces  of  meat,  broiling  practically  serves 
the  same  purpose  as  does  roasting  for  larger  pieces.  Frying,  as  usually  em- 
ployed, is  the  least  serviceable  method  of  preparation,  since  the  fat  or  other 
oily  material  used  so  permeates  the  food  as  to  render  it  difficult  of  penetration 
by  the  digestive  juices. 

Cooking  produces  upon  vegetables  the  necessary  effect  of  rendering  them 
softer,  so  that  they  can  be  more  readily  broken  up  in  the  mouth.  It  also 
causes  the  starch  grains  to  swell  up  and  burst,  and  so  aids  the  digestive  fluids 
in  penetrating  into  their  substance.  The  albuminous  matters  are  coagulated, 
and  the  gummy,  saccharine,  and  saline  matters  are  removed.  The  conversion 
of  flour  into  dough  is  effected  by  mixing  it  with  water,  and  adding  a  little  salt 
and  a  certain  amount  of  yeast.  Yeast  consists  of  the  cells  of  an  organized 
ferment  (Torula  cerevisice);  this  plant  in  its  growth  changes  by  ferment  action 
the  sugar  produced  from  the  starch  of  the  flour,  and  a  quantity  of  carbon 
dioxide  and  alcohol  is  formed;  the  gas  together  with  the  action  of  heat 
during  baking  causes  the  dough  to  rise,  and  the  gluten  being  coagulated,  the 
bread  sets  as  a  permanently  vesiculated  mass. 

THE  PROCESS  OF  DIGESTION. 

The  Enzymes.  The  digestive  process  involves  both  mechanical 
and  chemical  changes.  The  former  are  secured  by  the  crushing  and  grinding 
in  the  mouth,  together  with  the  mixing  and  kneading  that  come  from  the 
peristalses  of  the  stomach  and  intestine.  The  chemical  changes  are  the 
most  important  factors  of  the  digestive  process.  The  various  secretions  that 
are  poured  into  the  mouth,  stomach,  and  intestines  all  contain  substances 
which  react  on  the  foods  to  render  the  latter  more  soluble.  The  special  agency 
in  each  secretion  is  the  presence  of  representatives  of  the  chemical  groups 
known  as  enzymes.     These  enzymes,  or  unorganized  ferments,  are  the  essen- 


30*2  FOOD     AND     DIGESTION 

lial  factors  in  the  secretions  which  produce  the  chemical  changes  in  the 
foods.  Their  predominant  action  is  one  of  hydrolytic  cleavage;  that  is, 
the  substance  acted  upon  takes  up  water  and  then  splits  into  two  different 
substances,  usually  of  the  same  class.  The  chemical  nature  of  the  en- 
zymes is  as  yet  undetermined  because  of  the  difficulty  of  getting  absolutely 
pure  specimens.  Their  mode  of  action  is  at  present  regarded  in  the  nature 
of  catalysis.  That  is  to  say,  the  enzymes  by  their  presence  facilitate  reactions 
that  would  otherwise  take  place,  but  very  slowly.  Practically  all  are 
secreted  in  the  glands  as  zymogens,  which  bear  the  same  relation  to  enzymes 
as  fibrinogen  does  to  fibrin ;  they  are  transformed  to  enzymes  by  the  proper 
stimulus,  but  never  exist  as  such  in  the  glands. 

Each  enzyme  has  a  special  point  of  temperature  at  which  it  acts  best,  and 
any  change  in  the  temperature  retards  its  action;  the  action  is  suspended  at 
a  definite  point  of  low  temperature,  but  the  enzyme  is  not  destroyed  by  cold. 
The  action  is  suspended  at  a  somewhat  higher  temperature,  and  at  a  still 
higher  point  the  enzyme  is  destroyed.  Some  enzymes  act  only  in  an  alka- 
line medium,  being  destroyed  in  an  acid  medium,  and  vice  versa.  Others 
act  in  either  alkaline,  or  neutral,  or  acid  media.  Enzymes  are  hindered  in 
their  action  by  the  accumulation  of  the  products  of  their  activity.  Most  of 
them  cease  acting  altogether  when  these  products  reach  a  certain  concentra- 
tion, but  will  begin  acting  again  on  the  removal  of  these  products  or  if  the 
mixture  be  simply  diluted. 

The  quantity  of  the  enzyme  determines  the  rapidity  of  the  action,  but  not 
the  amount;  a  small  quantity  will  digest  as  much  as  a  large  quantity,  but  will 
take  longer.  The  enzymes  are  not  used  up  in  the  course  of  their  activity, 
as  far  as  can  be  seen,  and  do  not  seem  to  undergo  any  change  in  their  com- 
position. 

Enzymes  are  more  or  less  specific  in  their  action.  That  is,  each  enzyme 
is  supposed  to  produce  its  change  in  only  one  particular  substance,  as  in 
starch,  maltose,  proteid,  fat,  etc.  An  enzyme  that  can  cause  cleavage  of  the 
starch  molecule  will  not  act  on  fat  or  proteid  or  even  on  other  members  of 
the  starch  group.  This  specific  action  is  doubtless  expressive  of  a  definite 
relation  between  the  structure  of  the  enzyme  and  the  substance  acted  on. 

An  interesting  fact  as  to  enzyme  action  is  its  reversibility — a  phenomenon 
now  well  known  and  well  established  for  carbohydrates  and  fats.  Kastle  and 
Lowenhart  have  shown  that  lipase,  which  acts  to  split  neutral  fats  into 
fatty  acid  and  glycerin,  will  also  produce  a  synthesis,  at  least  of  butyric 
acid  and  alcohol  into  ethylbutyrate.  Taylor  and  Robertson  in  independ- 
ent papers  have  recently  made  the  far-reaching  discovery  that  the  proteid' 
molecule  can  be  synthesized  by  the  agency  (apparent  reversible  action)  of 
enzymes. 

Enzymes  are  classified  either  according  to  the  chemical  nature  of  their 
action  or  according  to  the  class  of  substances  on  which  they  act;  the  former 


DIGESTION     IN    THE     MOUTH  30o 

classification  is  more  logical,  but  the  latter  is  more  convenient  and  more  gen- 
erally used. 

Table  of  Digestive  Enzymes. 

Amylolytic. 

Ptyalin  of  saliva,  and  amylopsin  of  pancreatic  juice,  change  starch  to  maltose.  Malt- 
ose in  the  saliva,  and  pancreatic  juice  in  the  small  intestine,  change  maltose  to  dextrose. 
Lactase  splits  lactose  to  galactose  and  dextrose,  and  invertase  splits  cane-sugar  to  levulose 
and  dextrose  in  the  small  intestine. 

Lipolytic. 

Steapsin  or  lipase,  found  in  the  pancreatic  juice,  splits  neutral  fats  into  glycerin  and 
fatty  acid. 
Proteolytic. 

Pepsin  of  the  gastric  secretion,  and  trypsin  of  the  pancreatic  secretion,  change  pro- 
teids  to  proteoses  and  peptones,  trypsin  breaking  the  proteid  down  to  simpler  nitrog- 
enous  products.     Erepsin  of  the  intestine  splits  peptones  to  simpler  products. 

Coagulating. 

Rennin  of  the  gastric  juice  coagulates  milk. 

Activating. 

Enterokinase  of  the  intestinal  juice  converts  trypsinogen  to  trypsin.     (Thrombokin 
of  the  blood  is  of  this  class.) 

DIGESTION  IN  THE  MOUTH. 

The  food  is  received  into  the  mouth,  and  is  subjected  to  the  action  of  the 
teeth  and  tongue,  being  at  the  same  time  mixed  with  the  first  of  the  digestive 
juices,  the  saliva.  It  is  then  swallowed,  and,  passing  through  the  pharynx 
and  esophagus  into  the  stomach,  is  subjected  to  the  action  of  the  gastric 
juice,  the  second  digestive  juice.  Thence  it  passes  into  the  small  intestines, 
where  it  meets  with  the  bile,  the  pancreatic  juice,  and  the  intestinal  juices,  all 
of  which  exercise  a  digestive  influence  upon  the  portion  of  the  food  not  already 
digested  and  absorbed.  In  the  large  intestine  some  further  digestion  and 
absorption  take  place,  and  the  residue  of  undigested  matter  leaves  the  body 
in  the  form  of  feces. 

Mastication.  The  act  of  mastication  is  performed  by  the  biting  and 
grinding  movement  of  the  lower  range  of  teeth  against  the  upper.  The 
simultaneous  movements  of  the  tongue  and  cheeks  assist  by  crushing  the 
softer  portions  of  the  food  against  the  hard  palate  and  gums,  thus  supplement- 
ing the  action  of  the  teeth,  and  by  returning  the  morsels  of  food  to  the  action 
of  the  teeth  as  they  are  squeezed  out  from  between  them  until  they  have  been 
sufficiently  chewed. 

The  simple  up-and-down  or  biting  movements  of  the  lower  jaw  are  per- 
formed by  the  temporal,  masseter,  and  internal  pterygoid  muscles,  the  action 
of  which  in  closing  the  jaws  alternates  with  that  of  the  digastric  and  other 
muscles  passing  from  the  os  hyoides  to  the  lower  jaw,  which  open  the  jaws. 
The  grinding  or  side  movements  of  the  lower  jaw  are  performed  mainly  by 
the  external  pterygoid  muscles,  the  muscle  of  one  side  acting  alternately  with 


304 


FOOD      AND      DIGESTION 


the  oilier.  When  both  external  pterygoids  acl  together,  the  lower  jaw  is  pulled 
directly  forward,  so  that  the  lower  incisor  teeth  are  brought  in  front  of  the  level 
of  the  upper. 

The  act  of  mastication  is  voluntary.  It  will  suffice  here  to  state  that  the 
afferent  nerves  chiefly  concerned  are  the  sensory  branches  of  the  fifth  and 
tenth  or  glossopharyngeal,  and  the  efferent  are  the  motor  branches  of  the 
fifth  and  the  twelfth,  or  hypoglossal,  cerebral  nerves. 

The  act  of  mastication  is  much  assisted  by  the  saliva,  which  is  secreted  by 
the  salivary  glands  in  largely  increased  amount  during  the  process.  The 
intimate  incorporation  of  the  saliva  with  the  food  is  termed  insalivation. 

The  Salivary  Glands.  The  glands  which  secrete  the  saliva  in 
the  human  subject  are  the  salivary  glands  proper,  the  parotid,  the  submaxil- 
lary, and  the  sublingual,  and  numerous  smaller  bodies  of  similar  structure, 
and  with  separate  ducts,  which  are  scattered  thickly  beneath  the  mucous 
membrane  of  the  lips,  cheeks,  soft  palate,  and  root  of  the  tongue. 


Fig.    248. 


Fig. 


249. 


Fig.  248. — Section  of  the  Submaxillary  Gland  of  a  Dog,  Resting  Stage.  Most  of  the  Alveolar 
cells  are  large  and  clear,  being  filled  with  the  material  for  secretion  (in  this  case,  mucigen),  which 
obscures  their  protoplasm;  some  of  the  cells,  however,  are  small  and  protoplasmic,  forming  the 
crescents  seen  in  most  of  the  alveoli.      (Ranvier.) 

Fig.  249. — Section  of  a  Similar  Gland  after  a  Period  of  Activity.  The  mucigen  has  been  dis- 
charged from  the  mucin-secreting  cells,  which  consequently  appear  shrunken  and  less  clear.  Both 
the  cells  and  the  alveoli  are  much  smaller,  and  the  protoplasm  of  the  cells  is  more  apparent.  The 
crescents  of  Gianuzzi  are  enlarged,  c.  Crescent  cells;  g,  mucus-secreting  cells;  /,  lumen  of  alveolus. 
(Ranvier.) 


Histological  Structure.  The  salivary  glands  are  compound  tubular 
or  tubulo-racemose  glands.  They  are  made  up  of  lobules.  Each  lobule  con- 
sists of  the  branchings  of  a  division  of  the  main  duct  of  the  gland,  which 
are  generally  more  or  less  convoluted  toward  the  extremities,  that  form  the 
alveoli,  or  proper  secreting  parts  of  the  gland.  The  salivary  secreting  cells 
are  of  cubical  or  columnar  form  and  are  arranged  around  a  central  canal. 
The  granular  appearance  frequently  seen  in  the  salivary  cells  is  due  to  the 
numerous  zymogen  granules  which  they  contain. 

During  the  rest  period  the  cells  are  larger,  highly  granular,  with  obscured 


NERVOUS     MECHANISM     OF    THE     SECRETION     OF    SALIVA  305 

nuclei  and  smaller  lumen.  During  activity  the  cells  become  smaller  and 
their  contents  more  opaque. 

When  the  mucous  type  of  gland  is  secreting,  or  on  stimulation  of  the  nerve, 
mucigen  is  converted  into  mucin,  the  cells  swell  up,  appear  more  transparent, 
and  stain  deeply  in  logwood,  figure  249.  After  stimulation,  the  cells  become 
smaller,  more  granular,  and  more  easily  stained,  from  having  discharged  their 
contents,  and  the  nuclei  appear  more  distinct. 

Nerves  of  large  size  are  found  in  the  salivary  glands.  They  are  principally 
contained  in  the  connective  tissue  of  the  alveoli,  and  certain  glands,  especially 
in  the  dog,  are  provided  with  ganglia.  Some  nerves  have  special  endings  in 
Pacinian  corpuscles,  some  supply  the  blood-vessels,  and  others  penetrate  the 
basement  membrane  of  the  alveoli  and  end  upon,  but  not  in,  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the  ducts  of  the 
alveoli,  being  carried  in  by  the  fibrous  trabecule  between  the  alveoli,  in  which 
also  the  lymphatics  begin  by  lacunar  spaces. 

The  Nervous  Mechanism  of  the  Secretion  of  Saliva.  The  secretion 
of  saliva  is  under  the  control  of  the  nervous  system.  Under  ordinary  con- 
ditions it  is  excited  by  the  stimulation  of  the  peripheral  branches  of  two 
nerves,  the  gustatory  or  Ungual  branch  of  the  inferior  maxillary  division 
of  the  fifth  nerve,  and  of  the  glosso-pharyngeal,  which  are  distributed  to  the 
mucous  membrane  of  the  tongue  and  pharynx  conjointly.  The  stimulation 
occurs  on  the  introduction  of  sapid  substances  into  the  mouth,  and  the 
secretion  is  brought  about  in  the  following  way:  From  the  terminations  of 
the  above-mentioned  sensory  nerves  distributed  in  the  mucous  membrane 
an  impression  is  conveyed  upward  (afferent)  to  the  special  nerve  center 
situated  in  the  medulla  oblongata  which  controls  the  process,  and  by  it  is 
reflected  to  certain  nerves  supplied  to  the  salivary  glands,  which  will  be  pres- 
ently indicated.  In  other  words,  the  center,  when  stimulated  to  action  bv 
the  sensory  impressions  carried  to  it,  sends  out  impulses  along  efferent  or 
secretory  nerves  supplied  to  the  salivary  glands.  These  cause  the  saliva  to 
be  secreted  by  and  discharged  from  the  gland  cells.  Other  stimuli,  however, 
besides  that  of  the  food,  and  other  sensory  nerves  than  those  mentioned, 
may  reflexly  produce  the  same  effects.  For  example,  saliva  may  be  caused 
to  flow  by  irritation  of  the  mucous  membrane  of  the  mouth  with  mechanical, 
chemical,  electrical,  or  thermal  stimuli,  also  by  the  irritation  of  the  mucous 
membrane  of  the  stomach  in  some  way,  as  in  nausea  which  precedes  vomiting, 
when  some  of  the  peripheral  fibers  of  the  vagi  are  irritated.  Stimulation  of 
the  olfactory  nerves  by  smell  of  food,  of  the  optic  nerves  by  the  sight  of  it,  and 
of  the  auditory  nerves  by  the  sounds  which  are  known  by  experience  to  ac- 
company the  preparation  of  a  meal  may  also  stimulate  the  nerve  center  to 
action.  In  addition  to  these,  as  a  secretion  of  saliva  follows  the  movement 
of  the  muscles  of  mastication,  it  may  be  assumed  that  this  movement  stimu- 
lates the  secreting  nerve  fibers  of  the  gland,  direct  or  reflexlv.  From  the  fact 
20 


306  FOOD     AND     DIGESTION 

that  the  flow  of  saliva  may  be  increased  or  diminished  by  mental  states,  it 
is  evident  that  impressions  from  the  cerebrum  also  are  capable  of  stimulating 
the  center  to  action  or  of  inhibiting  its  action. 

Influence  of  Nerves  on  the  Submaxillary  Gland.  The  submaxillary 
gland  has  been  the  gland  chiefly  employed  for  the  purpose  of  experimentally 
demonstrating  the  influence  of  the  nervous  system  upon  the  secretion  of  saliva, 
because  of  the  comparative  facility  with  which  the  gland,  with  its  blood- 
vessels and  nerves,  can  be  exposed  to  view  in  the  dog,  rabbit,  and  other 
animals. 

The  chief  nerves  supplied  to  the  gland  are:  (i)  the  chorda  tympani,  a 
branch  given  off  from  the  facial  in  the  canal  through  which  it  passes  in  the 
temporal  bone;  and  (2)  branches  of  the  sympathetic  nerve  from  the  plexus 
around  the  facial  artery  and  its  branches  to  the  gland.  The  chorda,  figure 
250,  ch.  t,  passes  downward  and  forward,  under  cover  of  the  external  ptery- 
goid muscle,  and  joins  the  lingual  or  gustatory  nerve,  proceeds  with  it  for  a 
short  distance,  and  then  passes  along  the  submaxillary-gland  duct,  sm.  d, 
giving  branches  to  the  submaxillary  ganglion,  sm.  gl,  and  sending  others  to 
terminate  in  the  superficial  muscles  of  the  tongue.  It  consists  of  fine  medul- 
lated  fibers  which  lose  their  medulla  in  the  gland.  If  this  nerve  be  exposed 
and  divided  anywhere  in  its  course  from  its  exit  from  the  skull  to  the  gland  no 
immediate  result  will  follow,  nor  will  stimulation  either  of  the  lingual  or  of 
the  glosso-pharyngeal  produce  a  flow  of  saliva.  But  if  the  peripheral  end 
of  the  divided  nerve  be  stimulated,  an  abundant  secretion  of  saliva  ensues, 
and  the  blood  supply  is  enormously  increased  by  dilatation  of  the  arteries.  The 
veins  may  even  pulsate,  and  the  blood  contained  within  them  is  more  arterial 
than  venous  in  character. 

When,  on  the  other  hand,  the  stimulus  is  applied  to  the  sympathetic  fila- 
ments (mere  division  producing  no  apparent  effect),  the  arteries  contract, 
and  the  blood  stream  is  in  consequence  much  diminished;  and  only  a  sluggish 
stream  of  dark  blood  escapes  from  the  veins.  The  saliva,  instead  of  being 
abundant  and  watery,  becomes  scanty  and  tenacious.  If  both  chorda  tym- 
pani and  sympathetic  branches  be  divided,  the  gland,  released  from  nervous 
control,  may  secrete  continuously  and  abundantly  (paralytic  secretion). 

The  abundant  secretion  of  saliva  which  follows  stimulation  of  the  chorda 
tympani  is  not  merely  the  result  of  a  filtration  of  fluid  from  the  blood-vessels, 
in  consequence  of  the  largely  increased  circulation  through  them.  This  is 
proved  by  the  fact  that,  when  the  main  duct  is  obstructed,  the  pressure  within 
may  considerably  exceed  the  blood  pressure  in  the  arteries,  and  also  that  when 
into  the  veins  of  the  animal  experimented  upon  some  atropine  has  been  previ- 
ously injected,  stimulation  of  the  peripheral  end  of  the  divided  chorda  pro- 
duces all  the  vascular  effects  as  before,  without  any  secretion  of  saliva  accom- 
panying them.  Again,  if  an  animal's  head  be  cut  off,  and  the  chorda  be 
rapidly  exposed  and  stimulated  with  an  interrupted  current,  a  secretion  of 


INFLUENCE     OF     NERVES     ON     THE     SUBMAXILLARY     GLAND         307 

saliva  ensues  for  a  short  time,  although  the  blood  supply  is  necessarily  absent. 
These  experiments  serve  to  prove  that  the  chorda  contains  two  sets  of  nerve 
fibers,  one  set,  vaso-dilator,  which,  when  stimulated,  act  upon  a  local  vaso- 
motor center  for  regulating  the  blood  supply,  inhibiting  its  action,  and  causing 
the  vessels  to  dilate,  and  so  producing  an  increased  supply  of  blood  to  the 
gland;  while  another  set,  which  are  paralyzed  by  injection  of  atropine,  directly 
stimulate  the  cells  themselves  to  activity,  whereby  the  cells  secrete  and  dis- 
charge the  constituents  of  the  saliva  which  they  produce,  the  secretory  nerves. 
These  latter  fibers  very  possibly  terminate  on  the  salivary  cells  themselves. 
If,  on  the  other  hand,  the  sympathetic  fibers  be  divided,  stimulation  of  the 


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Fig.  250. — Diagrammatic  Representation  of  the  Submaxillary  Gland  of  the  Dog  with  its  Nerves 
and  Blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several 
structures.)  sm.  gld..  The  submaxillary  gland  into  the  duct  (sm.  d.)  of  which  a  cannula  has  been 
tied.  The  sublingual  gland  and  duct  are  not  shown,  n.  I.,  n.  I'.,  The  lingual  or  gustatory  nerve; 
ch.  t.,  ch.  t'.,  the  chorda  tympani  proceeding  from  the  facial  nerve,  becoming  conjoined  with  the 
lingual  at  n.  /'.,  and  afterward  diverging  and  passing  to  the  gland  along  the  duct;  sm.  gl.,  submax- 
illary ganglion  with  its  roots;  n.  I.,  the  lingual  nerve  proceeding  to  the  tongue;  a.  car.,  the  carotid  ar- 
tery, two  branches  of  which,  a.  sm.  a.  and  r.  sm.  p.,  pass  to  the  anterior  and  posterior  parts  of  the  gland; 
v.  sm.,  the  anterior  and  posterior  veins  from  thegland  ending  in  v.  j..  the  jugular  vein;  v.sym.,  the 
conjoined  vagus  and  sympathetic  trunks;  gl.  cer.  s.,  the  superior- cervical  ganglion,  two  branches  of 
which  forming  a  plexus,  a.  /..  over  the  facial  artery,  are  distributed,  n.  sym.  sm.,  along  the  two  glan- 
dular arteries  to  the  anterior  and  posterior  portion  of  the  gland.  The  arrows  indicate  the  direction 
taken  by  the  nervous  impulses;  during  reflex  stimulations  of  the  gland  they  ascend  to  the  brain 
by  the  lingual  and  descend  by  the  chorda  tympani.      (M.  Foster.) 

tongue  by  sapid  substances,  or  electrical  stimulation  of  the  trunk  of  the  lin- 
gual or  of  the  glosso-pharyngeal,  continues  to  produce  a  flow  of  saliva.  From 
these  experiments  it  is  evident  that  the  chorda -tympani  nerve  is  the  principal 
nerve  through  which  efferent  impulses  proceed  from  the  center  to  excite  the 
secretion  of  this  gland. 

The  sympathetic  nerve  also  contains  two  sets  of  fibers,  vaso-constrictor 
and  secretory.  Rut  the  flow  of  saliva,  upon  stimulating  the  sympathetic,  is 
scanty,  and  the  saliva  itself  viscid.    At  the  same  time  the  vessels  of  the  gland 


308  FOOD     AND     DIGESTION 

arc  constricted.  The  secretory  fibers  may  be  paralyzed  by  the  administration 
of  atropine. 

Nerves  of  the  Parotid  Gland.  The  nerves  which  influence  secre- 
tion in  the  parotid  gland  are  branches  of  the  facial  (lesser  superficial  petrosal) 
and  of  the  sympathetic.  The  former  nerve,  after  passing  through  the  otic 
ganglion,  joins  the  auriculotemporal  branch  of  the  fifth  cerebral  nerve,  and, 
with  it,  is  distributed  to  the  gland.  The  nerves  by  which  the  stimulus  ordi- 
narily exciting  secretion  is  conveyed  to  the  medulla  oblongata,  are,  as  in  the 
case  of  the  submaxillary  gland,  the  fifth  and  the  glossopharyngeal.  The 
pneumogastric  nerves  convey  a  further  stimulus  to  the  secretion  of  saliva  when 
food  has  entered  the  stomach;  the  nerve  center  is  the  same  as  in  the  case  of 
the  submaxillary  gland. 

Changes  in  the  Gland  Cells.  The  method  by  which  the  salivary 
cells  produce  the  secretion  of  saliva  appears  to  be  divided  into  two  stages, 
which  differ  somewhat  according  to  the  class  to  which  the  gland  belongs,  viz., 
whether  to  (i)  the  true  salivary,  or  to  (2)  the  mucous  type.  In  the  former 
case,  it  has  been  noticed,  as  already  described,  that  during  the  rest  which 
follows  an  active  secretion  the  lumen  of  the  alveolus  becomes  smaller,  the 
gland  cells  larger  and  very  granular.  During  secretion  the  alveoli  and  their 
cells  become  smaller,  and  the  granular  appearance  in  the  latter  to  a  consider- 
able extent  disappears,  and  at  the  end  of  secretion  the  granules  are  confined 
to  the  inner  part  of  the  cell  nearest  to  the  lumen,  which  is  now  quite  distinct, 
figure  251. 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the  act  of 
secretion  consists  in  the  protoplasm  of  the  salivary  cell  taking  up  from  the 
lymph  certain  materials  from  which  it  manufactures  the  elements  of  its  own 


Fig.  251. — Alveoli  of  True  Salivary  Gland.     A,  At  rest;    B,  in  the  first  stage  of  secretion;    C, 
after  prolonged  secretion.      (Langley.) 

secretion,  and  which  are  stored  up  in  the  form  of  granules  in  the  cell  during 
rest;  the  second  stage  consists  of  the  actual  discharge  of  these  granules,  with 
or  without  previous  change.  The  granules  are  zymogen  granules,  and  repre- 
sent the  chief  substance  of  the  salivary  secretion,  ptyalin.  In  the  case  of  the 
submaxillary  gland  of  the  dog,  at  any  rate,  the  sympathetic  nerve  fibers  appear 
to  have  to  do  with  the  first  stage  of  the  process,  and  when  stimulated  the  proto- 


SALIVA  309 

plasm  is  extremely  active  in  manufacturing  the  granules,  whereas  the  chorda 
tympani  is  concerned  in  the  production  of  the  second  act,  the  actual  discharge 
from  the  cells  of  the  materials  of  secretion,  together  with  a  considerable 
amount  of  fluid,  the  latter  being  an  actual  secretion  by  the  protoplasm,  as 
it  ceases  to  occur  when  atropine  has  been  subcutaneously  injected. 

In  the  mucus-secreting  gland,  the  changes  in  the  cells  during  secretion 
have  been  already  spoken  of.  They  consist  in  the  gradual  production  by  the 
protoplasm  of  the  cell  of  a  substance  called  mucigen,  which  is  converted  into 
mucin,  and  discharged  on  secretion  into  the  canal  of  the  alveoli.  The  mucigen 
is,  for  the  most  part,  collected  into  the  inner  part  of  the  cells  during  rest, 
pressing  the  nucleus  and  the  small  portion  of  the  protoplasm  which  remains, 
against  the  limiting  membrane  of  the  alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with  that  of 
glands  in  general.  The  cells  which  line  the  ultimate  branches  of  the  ducts 
are  the  agents  by  which  the  special  constituents  of  the  saliva  are  formed.  The 
material  which  they  have  incorporated  within  themselves,  which  is  doubtless 
a  product  of  the  metabolism  of  the  protoplasm  of  the  cells,  is  given  up  again 
almost  at  once  in  the  form  of  a  fluid,  secretion,  which  escapes  from  the  ducts 
of  the  gland.  The  cells  themselves  undergo  diminution  in  the  mass  of  their 
protoplasm,  which  is  again  renewed  in  the  intervals  of  the  active  exercise  of 
the  functions.  The  source  whence  the  cells  obtain  the  materials  for  the  con- 
struction of  secretion  is  the  blood-plasma,  which  is  filtered  off  from  the  circu- 
lating blood  into  the  interstices  of  the  glands,  as  in  all  living  tissues. 

Saliva.  Saliva,  as  it  commonly  flows  from  the  mouth,  is  the  mixed 
secretion  of  the  salivary  glands  proper  and  of  the  glands  of  the  buccal  mucous 
membrane  and  tongue.  When  obtained  from  parotid  ducts,  and  free  from 
mucus,  saliva  is  a  transparent  watery  fluid,  the  specific  gravity  of  which  varies 
from  1004  to  1008,  and  in  which,  when  examined  with  the  microscope,  are 
found  floating  a  number  of  minute  particles,  derived  from  the  secreting  ducts 
and  vesicles  of  the  glands.  In  the  impure  or  mixed  saliva  are  found,  besides 
these  particles,  numerous  epithelial  scales  separated  from  the  surface  of  the 
mucous  membrane  of  the  mouth  and  tongue,  and  the  so-called  salivary  cor- 
puscles, discharged  probably  from  the  mucous  glands  of  the  mouth  and  the 
tonsils,  which  subside  when  the  saliva  is  collected  in  a  deep  vessel  and  left  at 
rest.  They  form  a  white  opaque  sediment  leaving  the  supernatant  fluid  trans- 
parent and  colorless,  or  with  a  pale  bluish-gray  tint.  Saliva  also  contains 
various  kinds  of  micro-organisms  (bacteria).  The  saliva,  when  first  secreted, 
appears  to  be  always  alkaline  in  reaction  ;  the  alkalinity  is  about  equal  to  .08 
per  cent  of  sodium  carbonate,  and  is  due  to  the  presence  of  disodium 
phosphate,  Na2HP04. 

The  mucin  is  the  largest  representative  of  the  organic  nitrogenous  class 
of  bodies  in  the  saliva.  It  may  be  thrown  down  by  addition  of  acetic  acid. 
It  gives  the  three  chief  proteid  reactions,  and  may  easily  be  split  up  by  the 


310  FOOD     AND     DIGESTION 

action  of  a  dilute  mineral  acid  into  globulin  and  a  carbohydrate  whose  exact 
character  has  not  yet  been  established,  though  it  resembles  a  sugar  in  reducing 
copper- sulphate  solutions.  The  presence  of  potassium  sulphocyanide,  KCNS, 
in  saliva  may  be  shown  by  the  blood-red  coloration  which  the  fluid  gives 
with  a  solution  of  ferric  chloride,  Fe2Cl6,  and  which  is  bleached  on  the  addition 
of  a  solution  of  mercuric  chloride,  HgCl2,  but  not  by  hydrochloric  acid. 

Chemical  Composition  of  Human  Saliva.      (Hammerbacher.) 

In  1,000  Parts. 

Water 994-2 

Solids 5-8 

Mucus  and  epithelium 2.2 

Soluble  organic  matter  (ptyalin) 1.4 

Potassium  sulphocyanide 0.04 

Salts 2.20 

Saliva  from  the  parotid  is  less  viscid;  less  alkaline,  the  first  few  drops 
discharged  in  secretion  being  even  acid  in  reaction;  clearer,  although  it  may 
become  cloudy  on  standing  from  the  precipitation  of  calcium  carbonate  by  the 
escape  of  carbon  dioxide;  and  more  watery  than  that  from  the  submaxillary. 
It  has  moreover  a  less  powerful  action  on  starch.  Sublingual  saliva  is  the 
most  viscid,  and  contains  more  solids  than  either  of  the  other  two,  but  has 
little  diastasic  action. 

Rate  of  Secretion  and  Quantity  of  Saliva.  The  rate  at  which  saliva 
is  secreted  is  subject  to  considerable  variation.  When  the  tongue  and  muscles 
concerned  in  mastication  are  at  rest,  and  the  nerves  of  the  mouth  are  subject 
to  no  unusual  stimulus,  the  quantity  secreted  is  not  more  than  sufficient  with 
the  mucus  to  keep  the  mouth  moist.  During  actual  secretion  the  flow  is  much 
accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies  greatly,  but  is  at  least 
1  liter. 

Function  of  Saliva.  The  purposes  served  by  saliva  are  mechanical 
and  chemical. 

Mechanical.  (1)  It  keeps  the  mouth  in  a  due  condition  of  moisture, 
facilitating  the  movements  of  the  tongue  in  speaking,  and  the  mastication 
of  food.  (2)  It  serves  also  in  dissolving  sapid  substances,  and  renders  them 
capable  of  exciting  the  nerves  of  taste.  (3)  But  the  principal  mechanical 
purpose  of  the  saliva  is  that,  by  mixing  with  the  food  during  mastication,  it 
makes  a  soft  pulpy  mass  such  as  may  be  easily  swallowed.  To  this  purpose 
the  saliva  is  adapted  both  by  quantity  and  quality.  For,  speaking  generally, 
the  quantity  secreted  during  feeding  is  in  direct  proportion  to  the  dryness 
and  hardness  of  the  food. 

Chemical.  The  chemical  action  which  the  saliva  exerts  upon  the  food  in 
the  mouth  is  to  convert  the  starchy  materials  which  it  contains  into  soluble 
starch  and  then  into  sugar.    This  power  the  saliva  owes  to  the  enzyme  ptyalin. 


FUNCTION    OF    SALIVA  311 

Certain  investigators  have  of  late  asserted  that  saliva  contains  another  enzyme, 
known  as  maltose,  which  has  the  power  of  splitting  the  disaccharides  into 
monosaccharides,  or  maltose  into  dextrose.  The  action  of  this  ferment  is 
certainly  very  limited.  The  conversion  of  the  starch  under  the  influence  of  the 
ferment  into  sugar  takes  place  in  several  stages,  and  in  order  to  understand 
it  a  knowledge  of  the  structure  and  composition  of  starch  granules  is  neces- 
sary. A  starch  granule  consists  of  two  parts:  an  envelope  of  cellulose,  which 
does  not  give  a  blue  color  with  iodine  except  on  addition  of  sulphuric  acid, 
and  of  granulose,  which  is  contained  within,  and  which  gives  a  blue  color 
with  iodine  alone.  Briicke  states  that  a  third  body  is  contained  in  the  granule, 
which  gives  a  red  color  with  iodine,  viz.,  erythro-granulose.  On  boiling,  the 
granulose  swells  up,  bursts  the  envelope,  and  the  whole  granule  is  more  or 
less  completely  converted  into  a  paste  or  gruel,  which  is  called  gelatinous 
starch. 

When  ptyalin  acts  upon  boiled  starch,  it  first  changes  the  latter,  by  hydro- 
lysis, into  soluble  starch,  or  amidulin;  this  is  more  limpid  and  more  like  a  true 
solution,  though  it  still  gives  the  blue  coloration  on  the  addition  of  iodine. 
This  stage  is  very  brief,  only  thirty  seconds  being  sometimes  required  in  labora- 
tory experiments  to  render  a  stiff  starch  paste  completely  fluid  when  a  few 
drops  of  saliva  are  added  at  body  temperature.  This  rapidity  of  action  is  of 
great  importance,  as  under  proper  conditions  of  mastication  practically  all 
the  boiled  starch  of  the  food  ought  to  enter  the  stomach  as  soluble  starch. 
When  the  starch  has  not  been  previously  boiled,  the  envelope  of  cellulose 
retards  the  action  of  the  ptyalin  to  a  very  marked  degree. 

Starch. 

Soluble  starch. 


Erythro-dextrin.  Maltose  and  iso-maltose. 


Achroo-dextrins.         Maltose  and  iso-maltose. 

The  further  stages  of  hydrolytic  cleavage  result  in  the  formation  of  a 
variable  mixture  of  maltose  and  iso-maltose  with  a  series  of  dextrins,  but  ap- 
parently never  result  (in  laboratory  experiments)  in  the  complete  conversion 
of  the  dextrins  into  sugars.  Gradually,  as  the  starch  is  converted,  the  blue 
coloration  with  iodine  is  replaced  by  a  purplish-red  and  finallv  by  a  red 
color:  the  latter  color  is  produced  by  erythro-dextrin  (so-called  from  the 
color).  In  the  later  stages  no  coloration  is  obtained  with  iodine,  and  for  this 
reason  the  dextrins  formed  are  known  as  achroo-dextrins;  there  are  probably 
several  of  these,  but  they  have  not  yet  been  sufficiently  isolated.  As  sugar 
appears  very  early  in  the  process,  even  at  the  stage  of  erythro-dextrin,  and 


.'312  FOOD    AND     DIGESTION 

gradually  increases  in  amount,  it  is  generally  concluded  that  maltose  is 
formed  early  in  the  decomposition  of  the  starch  molecule.  The  process  is 
usually  represented  schematically  as  above. 

The  sugars  formed  are  maltose  (C  H  O  )  and  a  closely  allied  sugar 
known  as  iso-maltose.  A  small  percentage  of  dextrose  has  been  found  by 
some  observers,  and  this  is  due  to  the  action  of  maltose.  Maltose  is  allied 
to  saccharose  or  cane-sugar  more  nearly  than  to  glucose;  it  is  crystalline;  its 
solution  has  the  property  of  polarizing  light  to  the  right  to  a  greater  degree 
than  solutions  of  glucose  (3  to  i);  it  is  not  so  sweet,  and  reduces  copper  sul- 
phate less  easily.  It  can  be  converted  into  glucose  by  boiling  with  dilute 
acids  and  by  the  action  of  the  enzyme  maltase  present  in  saliva. 

According  to  Brown  and  Heron  the  reactions  may  be  represented  thus: 
One  molecule  of  gelatinous  starch  is  converted  by  the  action  of  an  amylolytic  ferment  into 

n  molecules  of  soluble  starch. 
One  molecule  of  soluble  starch  =    10  (C12H20O10)  +  8  (H2O),  which  is  further  converted 
by  the  ferment  into 

1.     Erythro-dextrin,  9  (C12H20O11))   (giving  red  with  iodine)  +  Mal- 
tose (C12H22O1,). 
then  into  2.     Erythro-dextrin  8  (C12H20O10)  (giving  yellow  with  iodine)  -\-  Mal- 
tose   2    (Cl2H220n). 

next  into  3.     Achroo-dextrin  7  (C12H20O10)  +  Maltose  3  (C12H22O11). 
And  so  on;   the  resultant  being: 

Soluble  starch  10  (C12H20O10)  +  Water  8  (H2O)  =  Maltose  8  (C12H22O1,)  + 
Achroo-dextrin  2  (C12H20O10). 

Many  observers,  however,  believe  that  the  maltose  simultaneously  present 
with  erythro-dextrin  is  not  actually  split  off  from  the  starch  molecule  in  the 
formation  of  erythro-dextrin,  but  that  it  is  the  product  of  more  advanced  hydrol- 
ysis in  other  starch  molecules.  They  point  out  that  in  such  a  chemical  re- 
action of  considerable  time  duration,  it  is  improbable  that  all  the  starch  mole- 
cules are  attacked  at  the  same  rate  or  are,  at  any  given  moment,  equally 
advanced  in  cleavage.  Their  theory  is  that  there  is  a  series  of  more  and  more 
simple  dextrins  formed  giving  rise  finally  to  the  disaccharides. 

The  presence  of  sugar  in  such  an  experiment  is  at  once  discovered  by  the 
application  of  Trommer's  test,  which  consists  in  the  addition  of  a  drop  or 
two  of  a  solution  of  copper  sulphate,  followed  by  a  larger  quantity  of  caustic 
potash.  When  the  liquid  is  boiled,  an  orange-red  precipitate  of  copper  sub- 
oxide indicates  the  presence  of  sugar. 

Influences  which  Affect  the  Action  of  Saliva  on  Starch.  Moderate 
heat,  about  37.8°  to  400  C,  is  most  favorable  to  the  rapid  cleavage  of  starch 
by  the  ptyalin.  Cold  retards  and  o°  C.  suspends  the  action  but  does  not  de- 
stroy the  ferment.    A  temperature  of  6o°  C.  destroys  the  ptyalin. 

Removal  of  the  products  of  salivary  digestion  as  they  are  formed  facilitates 
the  action  of  the  enzyme,  as  an  excess  of  these  products  is  detrimental  to  further 
action. 

The  reaction  between  starch  and  saliva  takes  place  best  in  a  neutral  or 


SALIVARY    DIGESTION     IN    THE    STOMACH  313 

very  faintly  alkaline  medium  and  is  inhibited  by  strong  alkalies  and  especially 
by  acids  even  as  weak  as  the  acidity  of  the  gastric  juice.  This  last  is  of 
particular  importance  since  it  raises  the  question  as  to  how  long  the  ptyalin 
may  act. 

The  action  of  saliva  on  starch  is  not  limited  to  the  brief  interval  during 
which  food  remains  in  the  mouth,  as  is  now  well  known,  but  may  continue 
for  a  time  in  the  stomach. 

Ptyalin  is  strictly  an  amylolytic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which  the  saliva  acts 
chemically.  The  secretion  has  no  apparent  influence  on  gum,  cellulose,  or 
on  fat,  and  is  equally  destitute  of  power  over  albuminous  and  gelatinous  sub- 
stances. 

The  salivary  glands  of  children  do  not  become  functionally  active  till  the 
age  of  4  to  6  months,  and  hence  the  bad  effects  of  feeding  them  before  this 
age  on  starchy  food,  corn-flour,  etc.,  which  they  are  unable  to  render  soluble 
and  capable  of  absorption. 

Salivary  Digestion  in  the  Stomach.  Laboratory  experiments 
have  demonstrated  that  while  the  addition  of  even  0.05  per  cent  of  hydrochloric 
acid  will  inhibit  the  action  of  ptyalin  on  a  solution  of  starch,  if  any  proteids 
be  present  in  the  solution  much  more  acid  must  be  added  before  the  action 
of  the  ptyalin  is  stopped.  The  explanation  of  the  latter  fact  is  that  the  acid 
unites  with  the  proteids  in-  some  chemical  combination  forming  "  combined 
acid,"  which  has  little  effect,  comparatively,  on  ptyalin.  This  "  combined 
acid"  gives  a  red  color  with  litmus,  but  is  distinguished  from  free  acid  by 
giving  a  brownish  instead  of  a  bluish  color  with  Congo  red.  When  food  enters 
an  empty  stomach,  as  happens  at  the  beginning  of  a  meal  the  acid  first  com- 
bines with  the  proteid  food  stuffs  and  so  does  not  at  once  affect  the  ptyalin. 

A  still  more  important  fact  in  its  bearing  on  this  subject  was  recently 
discovered  by  Cannon,  who  showed  experimentally  that  starchy  foods  mixed 
with  weak  alkali  remain  alkaline  in  the  stomach  for  as  much  as  an  hour  and 
a  half.  Such  foods  when  swallowed  into  the  stomach  are  packed  away  in 
that  organ  in  a  mass.  The  secretion  of  the  acid  gastric  juice  comes  in  contact 
only  with  the  outer  surface  of  the  mass,  which  is  not  materially  disturbed  by 
the  stomach  peristalses.  The  center  of  the  mass  may,  therefore,  remain  alka- 
line until  the  outer  layers  are  completely  eroded  away,  and  the  ptyalin  may 
continue  to  act  on  starch  during  the  whole  time. 

DEGLUTITION. 

When  properly  masticated,  the  food  is  transmitted  in  successive  portions 
to  the  stomach  by  the  act  of  deglutition  or  swallowing.  The  following  account 
of  deglutition  is  based  upon  the  researches  of  Kronecker  and  Meltzer,  whose 
experiments  seem  to  modify  in  some  details  the  earlier  theory  of  Magendie: 


314  FOOD     AND     DIGESTION 

The  mouth  is  closed,  and  the  food  after  thorough  mixing  with  the  saliva 
is  rolled  into  a  bolus  on  the  dorsum  of  the  tongue.  The  tip  of  the  tongue  is 
pressed  upward  and  forward  against  the  hard  palate,  thus  shutting  off  the 
anterior  part  of  the  mouth  cavity.  The  mylo-hyoid  muscles  then  suddenly 
contract,  the  bolus  of  food  is  put  under  great  pressure  and  shot  backward  and 
downward  through  the  pharynx  and  into  the  esophagus  and,  if  the  food  be 
fluid  enough,  even  to  the  cardiac  orifice  of  the  stomach.     Coincidently  with 


:' 


(l? 


■ 


Fig.  252. — Transverse  Section  of  the  Human  Esophagus,  a.  Fibrous  covering;  b,  longi- 
tudinal muscular  fibers;  c,  transverse  muscular  fibers;  d,  areolar  or  submucous  coat;  e,  muscularis 
mucosae;  f,  mucous  membrane,  with  part  of  a  lymphoid  nodule;  g,  stratified  epithehal  lining;  h, 
mucous  gland;   *,  gland  duct;   m',  striated  muscle  fibers.     (V.  Horsley.) 

the  contraction  of  the  mylo-hyoid  muscles,  the  hyoglossi  are  thrown  into 
action,  drawing  the  tongue  backward  and  downward,  not  only  increasing 
the  pressure  upon  the  food,  but  forcing  the  epiglottis  over  the  glottis,  closing 
the  larynx. 

It  has  been  shown  by  the  Roentgen-ray  method  that  the  character  of  the 
food  determines  somewhat  its  passage  through  the  esophagus.  The  dry 
and  semisolid  foods  are  seized  by  the  musculation  of  the  esophagus  and  passed 
down  that  organ  by  a  peristaltic  wave.  The  longitudinal  muscles  contract, 
tending  to  enlarge  the  diameter  of  the  esophagus  in  advance  of  the  food,  while 
contractions  of  the  circular  muscles  produce  pressure  on  the  bolus  just 
behind,  thus  forcing  it  along  to  the  cardia.  This  wave  reaching  the 
cardiac  orifice  about   six  seconds   after   the   commencement    of   the  act   of 


NEK  VOLS     MECHANISM     OF     DEGLUTITION  Si  5 

deglutition,  forces  the  food  into  the  stomach,  the  sphincter  having  previously 
relaxed.  The  interval  of  time  between  the  commencement  of  the  act  of  degluti- 
tion and  the  arrival  of  the  more  fluid  food  at  the  cardiac  orifice  of  the  stomach 
may  not  be  more  than  one-tenth  second,  though  it  remains  at  the  cardiac 
orifice  without  entering  the  stomach  until  the  first  parts  of  the  act  of  swal- 
lowing is  reinforced  by  the  subsequent  contraction  of  the  constrictors  of  the 
pharynx  and  the  passage  of  a  peristaltic  wave  down  the  esophagus.  In 
some  cases,  however,  the  liquid  food  is  not  stopped  at  the  cardiac  orifice, 
but  is  sent  through  the  relaxed  sphincter  by  the  original  force  of  the 
mylo-hyoid  contraction. 

In  man  the  esophagus  was  said  to  contract  in  three  separate  segments, 
the  first  segment  lying  in  the  neck  and  being  about  six  centimeters  long,  the 
second  being  the  next  ten  centimeters  of  the  tube,  and  the  third  the  remaining 
portion  to  the  stomach.  But  the  later  Roentgen-ray  observations  show  no 
break  in  the  continuous  passage  of  the  food,  though  the  movement  of  the  food 
is  slower  in  the  lower  segment  of  the  esophagus. 

The  act  of  swallowing  consists,  then,  of  the  contraction  in  sequence  of 
the  mylo-hyoids,  the  constrictors  of  the  pharynx,  and  the  esophagus.  The 
computed  time  of  contraction  is  as  follows: 

Seconds. 

Contraction  of  mylo-hyoids  and  constrictors  of  the  pharynx 0.3 

Contraction  of  the  first  part  of  the  esophagus 0.9 

Contraction  of  the  second  part  of  the  esophagus 1.8 

Contraction  of  the  third  part  of  the  esophagus 3.0 

6.0 

If  a  second  attempt  at  swallowing  be  made  before  the  first  has  been  com- 
pleted (that  is,  before  six  seconds  have  elapsed),  the  remaining  portion  of  the 
first  act  is  inhibited,  and  the  contraction  wave  reaches  the  stomach  six  sec- 
onds after  the  commencement  of  the  second  act. 

During  the  act  of  deglutition  the  posterior  nares  are  closed  through  the 
action  of  the  levator  palati  and  tensor  palati  muscles,  which  raise  the  velum; 
the  palato-pharyngei,  drawing  the  posterior  pillars  of  the  fauces  together; 
and  the  azygos  uvulae,  which  raises  the  uvula — thus  forming  a  complete  curtain. 
Otherwise  the  food  would  pass  into  the  nose,  as  happens  in  the  case  of  cleft 
palate.  At  the  same  time  the  larynx  is  closed  by  the  adductor  muscles  of  the 
vocal  cords  and  the  descent  of  the  epiglottis,  the  larynx  being  drawn  upward 
as  a  whole  through  the  action  of  the  mylo-hyoid,  genio-hyoid,  thyro-hyoid, 
and  digastric  muscles.  The  presence  of  the  epiglottis  is  not  necessary  for  the 
completion  of  the  act  of  degi.itition. 

Nervous  Mechanism  of  Deglutition.  The  sensory  nerves  engaged 
in  the  reflex  act  of  deglutition  arc  branches  of  the  fifth  cerebral  supplying  the 
soft  palate;  glossopharyngeal,  supplying  the  tongue  and  pharynx;  the  superior 
laryngeal  branch  of  the  vagus,  supplying  the  epiglottis  and  the  glottis.     The 


316  FOOD     AND     DIGESTION 

motor  fibers  concerned  are  branches  of  the  fifth,  supplying  part  of  the  digastric 
and  mylo-hyoid  muscles  and  the  muscles  of  mastication;  the  facial,  supplying 
the  levator  palati;  the  glosso-pharyngeal,  supplying  the  muscles  of  the 
pharynx;  the  vagus,  supplying  the  muscles  of  the  larynx  through  the  in- 
ferior laryngeal  branch;  and  the  hypoglossal,  the  muscles  of  the  tongue.  The 
nerve  center  by  which  the  muscles  are  harmonized  in  their  action  is  situated 
in  the  medulla  oblongata.  It  cannot  be  definitely  circumscribed,  but  is  in 
the  general  level  of  the  vagus  origin.  The  movements  of  the  esophagus  are 
coordinated  by  the  complex  of  sensory,  and  motor  fibers  of  the  fifth  and  the 
ninth  to  twelfth  cranial  nerves,  which  all  take  some  part  in  this  complicated 
reflex. 

DIGESTION  IN  THE  STOMACH. 

The  stomach  in  man  and  those  mammalia  which  are  provided  with  a 
single  stomach  consists  of  a  dilatation  of  the  alimentary  canal  placed  between 
and  continuous  with  the  esophagus,  which  enters  its  larger  or  cardiac  end  on 
the  one  hand,  and  the  small  intestine,  which  commences  at  its  narrowed  end 
or  pylorus,  on  the  other.  It  varies  in  shape  and  size  according  to  its  state  of 
distention.  It  is  supplied  with  nerves  from  the  vagus  and  from  the  sympa- 
thetic and  receives  a  special  artery,  the  gastric  artery. 

Structure  of  the  Stomach.  The  stomach  is  composed  of  four 
coats,  called  respectively,  the  external  or  peritoneal,  the  muscular,  the  sub- 
mucous, and  the  mucous  coat.  Blood-vessels,  lymphatics,  and  nerves  are 
distributed  in  and  between  them. 

The  muscular  coat  consists  of  three  separate  layers  of  fibers  which,  accord- 
ing to  their  several  directions,  are  named  the  longitudinal,  circular,  and 
oblique.  The  longitudinal  set  are  the  most  superficial  and  are  continuous 
with  the  longitudinal  fibers  of  the  esophagus  and  spread  out  in  a  diverging 
manner  over  the  cardiac  end  and  sides  of  the  stomach  to  the  pylorus.  The 
circular  or  transverse  coat  more  or  less  completely  encircles  all  parts  of  the 
stomach;  this  coat  is  thickest  at  the  middle  and  in  the  pyloric  portion  of  the 
organ,  and  forms  the  chief  part  of  the  thick  ring  of  the  pylorus.  The  next 
and  consequently  deepest  coat,  the  oblique,  is  continuous  with  the  circular 
muscular  fibers  of  the  esophagus  at  the  cardiac  orifice  of  the  stomach.  This 
coat  is  quite  interrupted  and  more  or  less  incomplete.  The  muscular  fibers 
of  the  stomach  and  intestinal  canal  are  unstriated. 

The  mucous  membrane  of  the  stomach,  which  rests  upon  a  layer  of  loose 
cellular  membrane,  or  submucous  tissue,  is  smooth,  soft,  and  velvety.  It  is 
of  a  pale  pink  color  during  life,  and  in  the  contracted  state  is  thrown  into 
numerous  longitudinal  folds  or  ruga?,  which  disappear  when  the  organ  is 
distended.     It  is  composed  of  a  mass  of  short  tubular  secreting  glands. 

The  Gastric  Glands.  The  glands  of  the  mucous  membrane  of  the 
stomach  are  of  two  varieties,  Cardiac  and  Pyloric. 


THE     GASTRIC     GLANDS 


317 


Cardiat  glands  are  found  throughout  the  whole  of  the  cardiac  end  of  the 
stomach.  They  are  arranged  in  groups  of  four  or  five,  which  are  separated 
by  a  fine  connective  tissue.     Two  or  three  tubes  often  open  into  one  duct, 


~T 


Fig  253.— The  Human  Stomach  and  the  Vagus  Distribution.  R.  L.,  Recurrent  laryngeal; 
Ca2,  inferior  cervical  cardiac  branch;  Cas,  Ca4.  cardiac  branches  of  vagus;  A.  P.  PL,  P-  r.  PL. 
anterior  and  posterior  pulmonary  plexuses;  Oes.  PI.,  esophageal  plexus;  Cast.  K.  and  L.,  gastric 
branches  of  vagus,  right  and  left;    Coe.  PL.  coeliac  plexus;   Hep.  PL.  hepatic  plexus. 

figure  254,  which  forms  about  a  third  of  the  whole  length  of  the  tube  and 
opens  on  the  surface.    The  ducts  and  the  free  surface  are  lined  with  columnar 


318 


!•<><>  I)     AN' I)     DIGESTION 


epithelium.  The  bod)  <>l  the  gland  is  composed  of  granular  secreting  cells 
called  chief  cells  or  peptic  cells.  Between  these  cells  and  the  membrana  pro- 
pria of  the  tubes  are  large  oval  or  spherical  cells,  granular  in  appearance  with 
clear  oval  nuclei;  these  cells  are  call  oxyntic  or  parietal  cells.  They  do  not 
form  a  continuous  layer,  figure  254.  Intercellular  tubules  extending  from 
the  duct  of  the  gland  between  the  chief  cells  and  connecting  with  intracellular 

secretory  tubules  in  the  parietal  cells 
have  been  shown  by  the  Golgi  method, 
figure  256. 

As  the  pylorus  is  approached  the 
gland  ducts  become  longer  and  the 
tube  proper  becomes  shorter,  and  oc- 
casionally branched  at  the  fundus. 

The  Pyloric  Glands.  These  glands 
have  much  longer  ducts  and  larger 
mouths  than  the  peptic  glands. 


Fig.  254. 


Fig.  2S5. 


Fig.  254. — From  a  Vertical  Section  through  the  Mucous  Membrane  of  the  Cardiac  End  of 
Stomach.  Two  peptic  glands  are  shown  with  a  duct  common  to  both,  one  gland  only  in  part,  a, 
Duct  with  columnar  epithelium  becoming  shorter  as  the  cells  are  traced  downward;  n,  neck  of 
gland  tubes,  with  central  and  parietal  or  so-called  peptic  cells;  h,  fundus  with  curved  cecal  extrem- 
ity— the  parietal  cells  are  not  so  numerous  here.      X  400.      (Klein  and  Noble  Smith.) 

Fig.  255. — Cross-sections  at  Various  Levels  of  Peptic  Glands  of  Stomach.  X  400.  M, 
Section  through  gastric  pit  near  surface;  M'.  section  through  gastric  pit  near  bottom;  h,  mouth 
of  gland;  k,  neck;  g,  body  near  fundus;  the  chief  cells  are  shaded  lightly;  b,  parietal  cells. 
(Kolliker.) 


The  parietal  cells  are  absent  in  the  pyloric  glands.    The  pyloric  glands  be- 
come larger  as  they  approach  the  duodenum,  also  more  convoluted  and  more 


THE     GASTRIC     GLANDS 


319 


deeply  situated.    They  are  directly  continuous  with  Brunner's  glands  in  the 
duodenum  (Watney). 

Blood-vessels  and  Lymphatics.  The  blood-vessels  of  the  stomach  first 
break  up  in  the  submucous  tissue  and  send  branches  upward  between  the 
closely  packed  glandular  tubes,  which  anastomose  around  them  by  a  fine 
capillary  network  with  oblong  meshes.  Contiguous  with  this  deeper  plexus, 
or  prolonged  upward  from  it,  so  to  speak,  is  a  more  superficial  network  of 
larger  capillaries,  which  branch  densely  around  the  orifices  of  the  tubes  and 


Fig.  256. 


Fig.  257. 


Fig.  256. — Longitudinal  Section  of  Fundus  of  Gland  from  Dog's  Stomach,  a,  Lumen  ol 
gland;  b,  intracellular  canals  in  parietal  cells;  c,  cut-off  portion  of  parietal  cell;  d,  chief  cells; 
e,  intercellular  canals  leading  from  lumen  of  gland  to  canals  in  parietal  cells.      (Bailey.) 

Fig.  257. — Tubule  of  Pyloric  Gland  of  Man.  (Highly  magnified.)  Note  the  thin  basal  layer 
of  cytoplasm;  the  reticular  cell  body  containing  secretion;  the  subdivision  of  the  latter  in  some 
cells  into  proximal  and  distal  masses. 


form  the  framework  on  which  are  molded  the  small  elevated  ridges  of  mucous 
membrane.  From  this  superficial  network  the  veins  chiefly  take  their  origin, 
pass  down  between  the  tubes,  with  no  very  free  connection  with  the  deeper 
intertubular  capillary  plexus,  and  open  finally  into  the  venous  network  in 
the  submucous  tissue. 

The  lymphatic  vessels  surround  the  gland  tubes  with  a  network.  Toward 
the  fundus  of  the  peptic  glands  are  masses  of  lymphoid  tissue  which  may 
appear  as  distinct  follicles,  somewhat  like  the  solitary  glands  of  the  small 
intestine. 


320 


FOOD     AND     DIGESTION 


Microscopic  Changes  in  the  Gastric  Glands  During  Secretion.  Lang- 
ley  has  made  a  study  of  the  histological  changes  in  the  glandular  tissues 
in  the  fresh  state.  He  finds  that  during  fasting  or  when  the  glands  are  at  rest 
the  chief  cells  arc  granular  throughout,  being  crowded  with  large  highly  re- 
fractive granules.  During  activity  these  granules  gradually  disappear  pro- 
gressively from  the  base  toward  the  border  of  the  cell  on  the  lumen  of  the  tube. 
They  no  doubt  represent  the  zymogen  substances  from  which  the  first  discharge 


Fig.  258. — Scheme  of  Blood-vessels  and  Lymphatics  of  Stomach.  X  70.  o,  Mucous  mem- 
brane; b,  muscularis  mucosae;  c,  submucosa;  d,  inner  circular  muscle  layer;  e,  outer  longitudinal 
muscle  layer;   .4,  blood-vessels;   B,  structure  of  coats;   C,  lymphatics.     (Szymonowicz,  after  Mall.) 

of  enzyme  is  derived  during  the  activity  of  secretion.  The  parietal  cells  are 
finely  granular  throughout,  though  they  decrease  in  size  during  activity,  as  in 
fact  do  the  chief  cells.  The  pyloric  cells  do  not  undergo  such  marked  changes, 
and  the  mucous  cells  of  the  more  superficial  layers  of  the  mucosa  cannot  be 
said  to  show  any  special  changes  at  the  time  of  digestional  activity  of  the 
other  layers.  During  periods  of  rest  the  gastric  cells  increase  in  size  and 
again  become  charged  with  granules  as  before. 

The  Act  of  Secretion  of  Gastric  Juice.  The  gastric  glands  un- 
dergo periods  of  rest  and  activity.  The  active  secretion  of  normal  gastric 
juice  takes  place  when  food  is  introduced  into  the  mouth,  or  in  fact  the 
mere  sight  of  appetizing  food  is  followed  by  an  abundant  secretion  of  gastric 
juice  as  shown  by  Bidder  and  Schmidt  on  a  dog  with  a  gastric  fistula.    Such 


THE     GASTRIC     JUICE 


321 


observations  strongly  indicate  that  the  act  is  a  nervous  phenomenon,  at  least 
under  nervous  control. 

Quite  recently  Pawlow  has  proved  that  secretory  fibers  are  carried 
to  the  gastric  glands  in  the  vagus  trunk.  His  experiment  consisted  in 
establishing  a  gastric  fistula,  and  some  days  later  in  dividing  the  esophagus 
in  the  neck  in  such  a  manner  that  any  food  swallowed  would  be  diverted 
to  the  exterior  through  the  cut  end.  A  "fictitious  meal"  could  then  be  given 
to  the  animal,  and  the  effect  upon  the  stomach  noted.  As  long  as  the  vagi 
were  intact,  certain  foods  (meats)  caused  a  flow  of  gastric  juice,  though 
none  of  the  food  reached  the  stomach.  The  secretion  of  gastric  juice  con- 
tinued for  hours  with  the  production  of  a  large  quantity  of  secretion.     When 


Fig.  259. — Very  Diagrammatic  Representation  of  the  Nerves  of  the  Alimentary  Canal.  Oc  to 
Ret,  the  various  parts  of  the  alimentary  canal  from  esophagus  to  rectum;  L.  V '.,  left  vagus,  ending  on 
front  of  stomach;  rl,  recurrent  laryngeal  nerve,  supplying  upper  part  of  esophagus;  R.  V .  right 
vagus,  joining  left  vagus  in  esophageal  plexus;  ce.  pi.,  supplying  the  posterior  part  of  stomach,  and 
continues  as  R'V  to  join  the  solar  plexus,  here  represented  by  a  single  ganglion,  and  connected 
with  the  inferior  mesenteric  ganglion,  m.  gl.\  a,  branches  from  the  solar  plexus  to  stomach  and  small 
intestine,  and  from  the  mesenteric  ganglia  to  the  large  intestine;  Spl.  maj.,  large  splanchnic  nerve, 
arising  from  the  thoracic  ganglia  and  rami  communicantes;  r.  c,  belonging  to  dorsal  nerves  from 
the  6th  to  the  9th  (or  10th);  Spl.  min.,  small  splanchnic  nerve  similarly  from  the  10th  and  nth 
dorsal  nerves.  These  both  join  the  solar  plexus,  and  thence  make  their  way  to  the  alimentary 
canal;  c.  r.,  nerves  from  the  ganglia,  etc.,  belonging  to  nth  and  12th  dorsal  and  1st  and  2d  lum- 
bar nerves,  proceeding  to  the  inferior  mesenteric  ganglia  (or  plexus),  m.  gl.,  and  thence  by  the  hypo- 
gastric nerve,  n.  hyp.,  and  the  hypogastric  nerve,  n.  hyp.,  and  the  hypogastric  plexus,  pi.  hyp.,  to  the 
circular  muscles  of  the  rectum;  /,  r.,  nerves  from  the  2d  and  3d  sacral  nerves,  S.  2,  S.  3  (nervi 
erigentes)  proceeding  by  the  hypogastric  plexus  to  the  longitudinal  muscles  of  the  rectum.  (M. 
Foster.) 


the  vagi  had  been  cut,  no  secretion  occurred.    Moreover,  he  found  that  direct 
stimulation  of  the  vagus  produced  a  flow  of  gastric  juice. 

Khigine  placed  foods  in  an  isolated  gastric  pouch  prepared  with  care  to 
maintain  the  nervous  relations  intact,  and  it  led  to  secretion  of  gastric  juice 
in  the  main  part  of  the  stomach.    This  is  undoubtedly  a  nervous  reflex  effect. 
21 


322 


FOOD     AND     DIGESTION 


Recently  observations  on  a  case  of  stricture  of  the  human  esophagus  which 
prevented  food  from  reaching  the  stomach  have  shown  that  an  abundant  flow 
of  gastric  juice  takes  place  when  food  is  taken  in  the  mouth. 

It  seems  conclusively  established  at  the  present  time  that  the  secretion  of 
gastric  juice  is  a  reflex  act  controlled  by  a  definite  nervous  mechanism.    This 


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!oui6 — 

1    J    3    A    5    *"   7    &    9    M  11   it 

„_ QumiUUj    oj  ocactunv. 

Fig.  260. — Table  to  Show  the  Secretion  of  Gastric  Juice  by  the  Dog.     (Khigine.) 

reflex  can  be  aroused  by  the  sensory  stimuli  of  taste,  smell,  and  even  sight. 
It  can  also  be  initiated  by  stimuli  arising  in  the  stomach  itself  by  the  effects 
of  ingredients  of  the  food  or  by  the  products  of  digestion.  Indeed  it  has  been 
shown  that  peptone  is  a  very  efficient  stimulus  for  this  stomach  reflex. 


THE    GASTRIC    JUICE  323 

The  influence  of  the  higher  nerve  centers  on  gastric  digestion,  as  in  the 
case  of  emotions,  is  too  well  known  to  need  more  than  a  reference. 

Immediately  on  the  introduction  of  food  or  other  stimulating  substance, 
the  mucous  membrane,  which  was  previously  quite  pale,  becomes  slightly 
turgid  and  reddened  with  the  influx  of  a  larger  quantity  of  blood,  and  the  gas- 
tric glands  commence  actively  to  secrete.  An  acid  fluid  ispoured  out  in  minute 
drops  and  the  secretion  may  continue  for  hours. 

The  Gastric  Juice.  The  first  analysis  of  gastric  juice  was  made  by 
Prout  on  a  small  and  impure  specimen.  Beaumont  made  an  elaborate  and 
classic  series  of  observations  on  the  gastric  secretion  of  Alexis  St.  Martin, 
in  whom  there  existed,  as  the  result  of  a  gunshot  wound,  an  opening  leading 
directly  into  the  stomach  near  the  upper  extrdmity  of  the  great  curvature 
and  three  inches  from  the  cardiac  orifice.  The  introduction  of  any  mechan- 
ical irritant,  such  as  the  bulb  of  a  thermometer,  into  the  stomach  through 
this  artificial  opening  excited  the  secretion  of  gastric  fluid.  This  was  drawn 
off,  and  was  often  obtained  to  the  extent  of  nearly  an  ounce. 

The  chemical  composition  of  human  gastric  juice  has  been  also  investigated 
by  Schmidt.  The  fluid  in  this  case  was  also  obtained  by  means  of  an  accidental 
gastric  fistula.  The  mucous  membrane  was  excited  to  action  by  the  intro- 
duction of  some  hard  matter,  such  as  dry  peas,  and  the  secretion  was  removed 
by  means  of  an  elastic  tube.  The  fluid  obtained  was  found  to  be  acid,  limpid, 
odorless,  with  a  specific  gravity  of  1002  to  10 10.  It  contained  a  few  cells  and 
some  fine  granular  matter.  The  analysis  of  the  fluid  obtained  in  this  way 
is  given  below.  Essentially  it  is  a  weakly  acid  fluid  containing  hydrochloric 
acid  and  two  enzymes,  pepsin  and  rennin,  with  possibly  a  third,  maltose.  The 
gastric  juice  of  dogs  and  other  animals  obtained  from  gastric  fistulas  shows 
some  difference  in  composition. 

Chemical  Composition  of  Gastric  Juice. 

Dogs.  Human. 

Water 971 .  17         994.4 

Solids 28 .  82  5 .  60 

Solids — 

Ferment — Pepsin 17.5  3  - 19 

Hydrochloric  acid  (free) 2.7  0.2 

Salts- 
Calcium,    sodium,    and    potassium    chlorides;      and     calcium, 

magnesium,  and  iron  phosphates 8.57  2.19 

The  quantity  of  gastric  juice  secreted  daily  has  been  variously  estimated; 
but  the  average  for  a  healthy  adult  may  be  assumed  to  range  from  2,000  to 
3,000  cubic  centimeters  in  the  twenty-four  hours. 

The  Acid  of  Gas  ric  Juice.  The  acidity  of  the  fluid  is  due  to  free 
hydrochloric  acid,  although  other  acids,  e.g.,  lactic,  acetic,  butyric,  are  not 
infrequently  to  be  found  therein  as  products  of  gastric  digestion  or  abnormal 


324  FOOD     AND     DIGESTION 

fermentation.  In  healthy  gastric  juice  the  amount  of  free  hydrochloric  acid 
is  usually  about  0.2  percent,  but  may  be  as  much  as  0.3  per  cent.  In  patho- 
logical conditions  it  may  be  entirely  absent,  or  may  amount  to  0.5  per  cent,  or 
even  more. 

Hydrochloric  acid  is  the  proper  acid  of  healthy  gastric  juice,  and  various 
tests  have  been  used  to  prove  this.  The  tests  depend  upon  changes  produced 
in  aniline  colors  by  the  action  of  hydrochloric  acid  even  in  minute  traces, 
whereas  lactic  and  other  organic  acids  have  no  such  action. 

An  aqueous  solution  of  oo-lropeolin,  a  bright  yellow  dye,  is  turned  red  on 
the  addition  of  a  minute  trace  of  hydrochloric  acid,  and  aqueous  solutions 
of  methyl  violet  and  gentian  violet  are  turned  blue  under  the  same  circum- 
stances. The  lactic  acid  sometimes  present  in  the  contents  of  the  stomach  is 
derived  partly  from  the  sarcolactic  acid  of  muscle  and  partly  from  lactic-acid 
fermentation  of  carbohydrates.  Lactic  acid  (C3H603),  if  present,  gives  the 
following  test.  A  solution  of  10  cubic  centimeters  of  a  4  per  cent  aqueous  solu- 
tion of  carbolic  acid,  20  cubic  centimeters  of  water,  and  one  drop  of  ferric 
chloride  is  made;  forming  a  blue-colored  mixture.  A  mere  trace  of  free  lactic 
acid  added  to  such  a  solution  causes  it  to  become  yellow,  whereas  hydro- 
chloric acid  even  in  large  amount  only  bleaches  it. 

The  proteid  matter  in  the  food  combines  to  some  extent  with  the  hydro- 
chloric acid,  which  then  is  known  as  combined  acid  and  does  not  redden  litmus 
paper.  As  this  combination  is  immediate,  it  follows  that  no  free  acid  is  found 
in  the  gastric  contents  until  the  amount  secreted  is  more  than  enough  to  satu- 
rate the  various  albuminous  affinities.  It  is  partly  for  this  reason  that,  as  al- 
ready mentioned,  salivary  digestion  may  continue  in  the  stomach  for  some 
time  after  the  commencement  of  gastric  digestion.  According  to  Ehrlich  the 
amount  necessary  to  saturate  the  affinities  of  100  grams  of  various  articles 
of  diet  is  as  follows: 

Beef  (boiled) 2.0  grams  of  pure  HC1. 

Mutton  (boiled) 1.9  " 

Veal  (boiled) 2.2  " 

Pork  (boiled) 1.6  " 

Ham  (boiled) 1.8  " 

Sweetbread  (boiled) 0.9  " 

Wheat  bread 0.3  " 

Rye  bread 0.5  " 

Swiss  cheese 2.6  " 

Milk  (100  c.c.) o'-32-o.42  " 

The  acid  is  chiefly  found  at  the  surface  of  the  mucous  membrane,  but  is 
in  all  probability  formed  by  the  parietal  cells  of  the  cardiac  glands,  hence 
called  oxyntic,  for  no  acid  is  formed  by  the  pyloric  glands  in  which  this 
variety  of  cell  is  absent.  It  seems  established  that  the  chlorides  of  the  blood 
are  the  source  of  the  hydrochloric  acid,  for  when  these  chloride  salts  are 
reduced  to   the  point  at  which  they  are  tenaciously  held  the  hydrochloric 


ACTION     OF     PEPSIN     AND     HYDROCHLORIC     ACID  l.>?5 

acid  is  no  longer  secreted.    One  can  only  guess  at  the  detail  by  which  the 
parietal  cells  secrete  the  acid. 

The  acid  probably  results  (Maly)  from  a  combination  of  common  salt 
with  monosodic  phosphate,  NaH2P04  +  NaCl  =  Na2HP04  +  HC1;  the 
disodic  phosphate  is  then  reconverted  by  the  action  of  carbonic  acid  and 
water,  Na,HP04  +  CO,  +  H,0  =  NaH,P04  +  NaHC03.  All  these 
salts  are  found  in  the  blood. 

The  Pepsin.  The  pepsin  of  the  gastric  juice  is  derived  from  the 
activity  of  the  chief  cells  of  the  fundic  glands.  The  zymogen  pepsinogen, 
which  is  its  immediate  precursor,  is  in  all  probability  represented  by  the  gran- 
ules of  the  resting  cells.  The  ferment  pepsin  does  not  exist  as  such  in  the  cells, 
for  an  extract  of  peptic  glands  in  0.2  per  cent  soda  solution  kept  at  400  C.  retains 
for  hours  its  power  to  digest  proteid  when  added  to  0.2  per  cent  hydrochloric 
acid.  If  the  extract  be  first  treated  with  acid  till  it  is  active,  then  neutralized 
and  kept,  it  quickly  loses  its  power  to  digest.  The  enzyme  is  destroyed  by 
the  treatment,  but  the  pro-enzyme  is  not  so  injured. 

Digestive  Action  of  Pepsin  and  Hydrochloric  Acid.  The  chief  func- 
tion of  gastric  juice  is  to  alter  the  proteid  food  stuffs  so  that  they  may 
be  readily  absorbed.  Less  important  functions  are  the  antiseptic  action  of 
the  hydrochloric  acid,  and  the  coagulation  of  milk.  The  chief  digestive  power 
of  the  gastric  juice  depends  on  the  pepsin  and  acid  contained  in  it,  both  of 
which  are  necessary  for  the' process  in  the  stomach. 

This  action  on  proteids  may  be  shown  by  adding  a  little  gastric  juice 
(natural  or  artificial)  to  some  flakes  of  fibrin  or  to  diluted  egg  albumin,  and 
keeping  the  mixture  at  a  temperature  of  about  37.8°  C.  (ioo°  F.).  It  is  soon 
found  that  the  fibrin  goes  into  solution  and  that  the  albumin  cannot  be  pre- 
cipitated on  boiling.  If  the  solution  be  neutralized  with  an  alkali,  a  precipitate 
of  acid  albumin  is  thrown  down.  After  a  while  the  acid  albumin  disappears, 
so  that  no  precipitate  results  on  neutralization,  and  proper  analysis  will  show 
that  all  the  fibrin  or  albumin  has  been  converted  into  other  proteid  substances, 
viz.,  proteoses  and  peptones.  The  process,  as  in  the  case  of  salivary  digestion, 
is  never  complete  and  the  final  result  is  always  a  mixture  of  peptones  with 
proteoses  which  cannot  be  further  peptonized.  The  relative  proportions,  of 
course,  depend  on  the  duration  of  the  process.  A  side  product  is  found  (as 
an  insoluble  residue)  in  artificial  gastric  digestion  which  gives  practically  all 
the  proteid  reactions  and  is  soluble  in  dilute  alkali,  though  insoluble  in  water, 
sodium  chloride,  or  dilute  acid.  This  is  known  as  anti-albumid  and  may  be 
changed  into  peptone  by  prolonged  digestion;  it  does  not  occur  in  physiologi- 
cal gastric  digestion.  The  commonest  proteose  is  the  one  formed  from  albumin 
and  is  known  as  albumose,  or  by  the  more  general  name  proteose;  this  name 
is  used  in  the  subsequent  descriptions  of  the  digestive  processes. 

All  classes  of  proteids  are  digested  by  gastric  juice,  leading  to  the  produc- 
tion of  proteoses  and  peptones.    The  change  is  indicated  besl  by  the  characters 


326  FOOD      AND      DIGESTION 

of  the  new  proteid  -formed.  Peptones  have  certain  characteristics  which 
distinguish  them  from  other  proteids.  They  are  diffusible,  i.e.,  they  possess 
the  property  of  passing  through  animal  membranes.  In  their  diffusibility 
peptones  differ  remarkably  from  egg  albumin,  and  on  this  diffusibility  depends 
one  of  their  chief  uses.  Egg  albumin  as  such,  even  in  a  state  of  solution,  would 
be  of  little  service  as  food,  inasmuch  as  its  diffusibility  renders  difficult  its 
absorption  or  in  the  case  of  insoluble  proteids  effectually  prevents  absorption 
into  the  blood-vessels  of  the  digestive  canal.  When  completely  changed  by 
the  action  of  the  gastric  juice  into  peptones,  albuminous  matters  diffuse  readily, 
and  are  thus  quickly  absorbed. 

Peptones  are  not  found  in  the  blood,  even  of  the  vessels  immediately  con- 
cerned in  absorption  from  the  stomach  and  intestines.  In  their  absorption, 
therefore,  by  the  epithelial  cells,  they  must  undergo  a  synthetic  change,  ap- 
pearing in  the  blood  as  albumins  and  globulins,  which  are  not  readily  diffu- 
sible and  which  occupy  the  same  plane  as  the  proteids  from  which  the  peptones 
were  derived.  The  previous  cleavage  to  proteoses  and  peptones  is  in  the 
nature  of  preparation  for  this  final  act  of  absorption. 

Products  at  Different  Stages  of  Gastric  Digestion.  The  proteid 
is  first  changed  into  syntonin,  or  acid  proteid,  by  the  combined  action  of  the 
pepsin  and  acid.  Though  the  acid  alone  is  capable  of  accomplishing  this 
step,  the  fact  that  it  does  not  do  so  physiologically  is  proven  by  the  great  length 
of  time  required,  in  laboratory  experiments,  for  the  change. 

The  next  change  is  the  conversion  of  the  syntonin  into  proteoses  which, 
according  to  Neumeister,  occurs  in  two  successive  stages.  The  first  of  these 
stages  is  the  conversion  of  syntonin  into  the  primary  proteoses,  i.e.,  proto- 
proteose  and  hetero-proteose.  The  second  is  the  conversion  of  both  proto- 
proteose  and  hetero-proteose  into  the  secondary  proteoses,  i.e.,  deutero-proteose. 
The  last  change  is  the  conversion  of  the  deutero-proteose  into  the  end  product 
peptone.  This  last  change  does  not  occur  completely  to  any  great  extent  and 
the  proteoses  always  predominate  in  the  digesting  mass.  Schematically  the 
changes  in  the  proteids  may  be  represented  as  follows: 

Proteid. 

i 
Syntonin  (acid  proteid). 


Proto-proteose.  Hetero-proteose. 

I  I 

Deutero-proteose  Deutero-proteose. 

I  I 

Peptone.  Peptone. 

The  action  of  pepsin  is  one  of  hydrolysis  and  the  products  are  hydrated 
forms  of  proteid.  The  acid  is  absolutely  essential  to  the  action  of  pepsin,  but 
it  also  aids  digestion  by  causing  the  proteids  to  absorb  water.    That  this  ac- 


MOVEMENTS     OF    THE     STOMACH  327 

tion  is  important  is  proven,  in  laboratory  experiments,  by  the  decreased 
length  of  time  required  for  digestion  when  fibrin  has  first  been  soaked  in  0.2 
per  cent  hydrochloric  acid  and  thus  caused  to  swell  with  the  absorption  of 
water  before  coming  in  contract  with  the  pepsin. 

Circumstances  Influencing  Gastric  Digestion.  A  temperature  of 
about  400  C.  is  most  favorable  to  gastric  digestion.  The  pepsin  is  de- 
stroyed by  a  temperature  of  550  (neutral)  to  650  C.  (acid  solution)  and  its 
action  is  retarded  and  suspended  by  low  temperatures.  It  is  inactive  in  neutral 
or  alkaline  solution,  for  an  acid  medium  is  necessary.  Hydrochloric  is  the 
best  acid  for  the  purpose,  but  nitric  acid  or  the  organic  acids  may  be  substi- 
tuted for  the  hydrochloric.  Excess  of  peptone  delays  the  action,  and  the 
removal  of  the  products  of  digestion  facilitates  the  process. 

Action  of  Rennin.  Milk  is  curdled,  the  casein  being  precipitated, 
and  then  dissolved.  The  curdling  is  due  to  a  special  ferment  of  the  gastric 
juice,  rennin,  and  is  not  due  to  the  action  of  the  free  acid  alone.  The  effect  of 
rennin,  which  is  obtained  from  the  fourth  stomach  of  a  calf,  has  long  been 
known,  as  it  is  used  extensively  to  cause  precipitation  of  casein  in  cheese  manu- 
facture.   The  ferment  rennin  is  active  in  a  neutral  solution  as  well  as  in  acid. 

Time  Occupied  in  Gastric  Digestion.  Under  ordinary  conditions, 
from  three  to  four  hours  may  be  taken  as  the  average  time  occupied  by  the 
digestion  of  a  meal  in  the  stomach.  But  many  circumstances  will  modify 
the  rate  of  gastric  digestion.  The  chief  are:  Thenatureot  the  food  taken  and 
its  quantity  (the  stomach  should  be  fairly  filled,  not  distended);  the  time  that 
has  elapsed  since  the  last  meal,  which  should  be  at  least  enough  for  the  stomach 
to  be  quite  clear  of  food;  the  amount  of  exercise  previous  and  subsequent  to 
a  meal  (gentle  exercise  being  favorable,  over-exertion  injurious  to  digestion); 
the  state  of  mind;  and  the  bodily  health. 

Summary  of  Changes  in  the  Food  in  Gastric  Digestion.  Briefly 
summarizing  the  action  of  gastric  juice,  the  facts  appear  as  follows:  Gastric 
juice  has  a  specific  digestive  action  on  proteid  foods  of  all  kinds,  converting 
them  into  the  more  soluble  proteoses  and  peptones.  The  action  is  due  to  an 
enzyme,  pepsin,  acting  in  and  with  an  acid,  hydrochloric  acid.  Digestion  takes 
place  best  at  the  temperature  of  the  body,  is  destroyed  by  high  heat  and  sus- 
pended by  cold,  o°  C.  Putrefaction  is  prevented  by  gastric  juice.  Milk  is 
first  coagulated  by  a  special  enzyme,  rennin,  and  then  digested  as  any  other 
proteid.  Gastric  juice  dissolves  soluble  substances  like  salts,  saccharides, 
etc.  Fats  and  carbohydrates  are  not  digested  by  gastric  juice,  in  fact  fats 
tend  to  hinder  the  action. 

MOVEMENTS    OF    THE    STOMACH. 

Attention  has  been  called  to  the  fact  that  the  stomach  is  a  muscular  sac 
capable  of  holding  quite  a  large  mass  of  food.     During  a  full  meal  as  much 


328  FOOD     AND     DIGESTION 

as  one  to  two  liters  or  more  of  semi-solid  food  is  packed  away  in  the  organ  in 
a  comparatively  short  space  of  time.  The  gastric  juice  is  secreted  by  the 
mucous  membrane  which  surrounds  the  surface  of  the  food  mass.  The  result 
is  that  the  secretion  begins  to  soften  and  digest  the  food  over  its  surface,  thus 
tending  to  liquefy  and  erode  away  layer  after  layer  of  the  food  mass.  The  pic- 
ture is  made  clearer  if  one  remembers  that  the  food  mass  is  retained  almost 
wholly  in  the  fundus  of  the  stomach.  The  pyloric  portion  of  the  stomach  is 
quite  strongly  muscular  and  quite  definitely  marked  off  by  the  strong  trans- 
verse band  at  its  union  with  the  fundus. 

The  gastric  juice  is  assisted  in  accomplishing  digestion  by  the  movements 
of  the  stomach  itself.  When  digestion  is  not  going  on,  the  stomach  is  uni- 
formly contracted,  its  orifices  not  more  firmly  than  the  rest  of  its  walls;  but, 
if  examined  shortly  after  the  introduction  of  food,  it  is  found  closely  encircling 
its  contents,  and  its  orifices  are  firmly  closed  like  sphincters.  The  cardiac 
orifice,  every  time  food  is  swallowed,  opens  to  admit  its  passage  to  the  stomach, 
and  immediately  closes  again.    The  pyloric  orifice,  during  the  taking  of  food 


Fig.  261. — Diagram  to  Show  the  Movement  of  Food  in  the  Pylorus  at  Times  when  the  Pyloric 

Valve  is  Closed. 

and  the  first  part  of  gastric  digestion,  is  so  completely  closed  that  none  of  the 
contents  escape. 

The  character  of  stomach  movements  has  been  admirably  determined  by 
recent  observers  using  the  Roentgen-ray  method.  Thus  Cannon  working 
with  cats  has  shown  that  in  from  five  to  ten  minutes  after  a  meal  slight  rings 
or  constrictions  occur  in  the  pyloric  antrum  and  travel  slowly  toward  the 
pyloric  valve  in  the  form  of  a  peristaltic  wave.  Successive  waves  begin  a  little 
further  back  toward  the  fundus  each  time  and  follow  over  the  pyloric 
antrum  with  clocklike  regularity,  in  the  cat  one  wave  in  ten  seconds,  which 
requires  in  each  case  about  twenty  seconds  for  its  completion.  In  man  they 
are  doubtless  slower.  These  peristalses  continue  during  the  whole  period  of 
digestion,  for  as  much  as  seven  or  even  more  hours. 

These  peristaltic  contractions  aid  the  gastric  juice  in  carrying  away  the 


MOVEMENTS     OF    THE    STOMACH 


329 


softened  layers  of  food  by  propelling  it  into  the  pylorus.  There  it  is  thoroughly 
mixed  with  the  gastric  juice,  forming  the  chyme.  Figure  261  gives  an  idea  of 
the  movement  of  the  food  in  the  antrum.  The  peristaltic  contractions  carry 
it  forward,  but  if  the  valve  does  not  open  to  permit  passage  to  the  duodenum, 
then  the  pressure  will  force  the  chyme  back  through  the  center  toward  the 
fundus.  After  several  minutes  the  pyloric  sphincter  will  occasionallv  relax 
to  allow  fluid  food  to  pass  to  the  duodenum,  but  when  more  solid  particles  come 


11A.M. 


12M. 


2RM. 


5P.M. 


Fig.  262. — Outlines  of    the    Roentgen-ray  Shadows  of  the  Stomach  Content  as    Digestion 

Progresses.     (Cannon.) 


up  against  the  valve  the  sphincter  promptly  contracts  and  remains  so  for  some 
time.  Toward  the  completion  of  digestion  even  solid  undigested  particles  are 
carried  on  into  the  intestine. 

The  movements  of  the  stomach  are  under  nervous  regulation.  Cannon 
found  that  the  peristalses  were  promptly  inhibited  in  cats  by  excitement.  Stim- 
ulation of  the  vagi  leads  to  contractions  of  the  stomach,  while  the  splanchnics 


330 


FOOD     AND     DIGESTION 


bring  about  relaxation  or  dilatation.  It  is  also  demonstrated  that  afferent 
vagus  impulses  influence  the  contractions  in  the  stomach. 

It  seems  probable  that  automatic  peristaltic  contraction  is  inherent  in  the 
muscular  coat  of  the  stomach,  and  that  the  central  nervous  system  is  only 
employed  to  regulate  it  by  impulses  passing  down  by  the  vagi  or  splanchnic 
nerves. 

Vomiting.  The  expulsion  of  the  contents  of  the  stomach  in  vomit- 
ing is  preceded  by  a  deep  inspiration  with  closure  of  the  glottis,  followed  im- 
mediately afterward  by  strong  contractions  of  the  muscles  of  the  abdomen, 
diaphragm,  and  stomach.  The  diaphragm  forms  an  unyielding  surface  against 
which  the  stomach  can  be  pressed.  In  this  way  as  well  as  by  its  own  contrac- 
tion the  diaphragm  is  fixed,  to  use  a  technical  phrase.  At  the  same  time  the 
cardiac  sphincter  muscle  is  relaxed,  and  the  orifice  which  it  naturally  guards  is 


FlG.  263. — Horizontal  Section  of  a  Small  Fragment  of  the  Mucous  Membrane,  including  one 
entire  crypt  of  Lieberkuhn  and  parts  of  several  others. 


actively  dilated.  The  pylorus  is  closed,  and,  the  stomach  itself  also  contracting, 
the  action  of  the  abdominal  muscles  produces  strong  compression  which  ex- 
pels the  contents  of  the  organ  through  the  esophagus,  pharynx,  and  mouth. 
Reversed  peristaltic  action  of  the  esophagus  probably  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite  passive  during 
vomiting,  and  that  the  expulsion  of  its  contents  is  effected  solely  by  the  pres- 
sure exerted  upon  it  when  the  capacity  of  the  abdomen  is  diminished  by  the 
contraction  of  the  diaphragm.  It  is  true  that  facts  are  wanting  to  demonstrate 
with  certainty  this  action  of  the  stomach  in  vomiting;  but  cases  of  fistulous 
opening  into  the  organ  appear  to  support  the  belief  that  it  does  take  place;  and 
the  analogy  of  the  case  of  the  stomach  with  that  of  the  other  hollow  viscera, 
as  the  rectum  and  bladder,  may  also  be  cited  in  confirmation. 

Vomiting  is  a  reflex  act.  It  can  be  excited  by  irritation  of  the  lining  of 
the  stomach  which  is  perhaps  the  normal  stimulus.  It  is  excited  by  stimula- 
tion or  irritation  of  other  parts  of  the  alimentary  tube,  i.e.,  the  pharynx,  the 


DIGESTION     IX    THE     INTESTINES 


331 


uvula,  the  intestine,  etc.  Vomiting  may  occur  from  stimulation  of  sensory 
nerves  from  many  organs,  e.g.,  kidney,  testicle,  etc.,  or  by  impulses  arising 
in  the  organs  of  special  sense,  the  eye,  olfactory  membrane,  etc.  The  sensory 
impulses  are  coordinated  by  a  nerve  center  located  in  the  medulla.  The 
center  may  also  be  stimulated  by  impressions  from  the  cerebrum  and  cere- 
bellum or  by  changes  arising  in  the  center  itself,  the  so-called  central  vomiting 
occurring  in  disease  of  those  parts.  The  efferent  impulses  are  carried  by  the 
phrenics  and  other  spinal  nerves  and  by  the  vagus. 

DIGESTION  IN  THE  INTESTINES. 

The  food  that  enters  the  small  intestine  has  already  been  subjected  to  two 
digestive  enzymes.  The  ptyalin  of  the  saliva  and  the  pepsin  of  the  gastric 
juice  together  with  the  mechanical  processes  involved  have  reduced  the  food 
to  a  pulpy  mass,  the  chyme.  This  peptonized  food  contains  most  of  the  total 
quantity  of  food  eaten,  little  having  been  absorbed  as  we  shall  see  later,  but 
much  of  the  starch  has  been  changed  to  soluble  maltose  and  dextrose  and 
the  proteid  to  albumoses  and  peptones.  The  discharge  from  the  stomach 
through  the  pyloric  valve  to  the  duodenum  has  been  going  on  through  three 


Fig.  204. 


Fig.  265. 


Fig.  264. — Piece  of  Small  Intestine  (previously  distended  and  hardened  by  alcohol).  Laid 
open  to  Show  the  Normal  Position  of  the  Valvule  Conniventes. 

Fig.  265. — Section  of  the  Pancreas  of  a  Dog  During  Digestion,  a.  Alveoli  lined  with  cells, 
the  outer  zone  of  which  is  well  stained  with  hematoxylin;  d,  intermediary  duct  lined  with  squa- 
mous epithelium.      X  350.      (Klein  and  Noble  Smith.) 


or  four  hours  on  an  average  for  each  full  meal.  This  stream  of  food  passing 
down  the  small  intestine,  slowly  because  of  the  valvulae  conniventes,  meets 
a  number  of  secretions  which  contain  enzymes  which  act  on  each  of  the  three 
great  food  principles,  proteids,  fats,  and  carbohydrates.  These  secretions  are 
the  pancreatic  fluid,  the  succue  entericus,  and  the  bile. 


332 


FOOD     AND     DIGESTION 


The  Pancreas.  The  pancreas  is  situated  within  the  curve  formed 
by  the  duodenum;  and  its  main  duct  opens  into  that  part  of  the  small  intestine 
through  a  duct  common  to  it  and  to  the  liver  and  about  two  and  a  half  inches 
from  the  pylorus. 

The  pancreas  bears  some  resemblence  in  structure  to  the  salivary  glands. 
Its  capsule  and  septa,  as  well  as  the  blood-vessels  and  lymphatics,  are  similarly 
distributed.  It  is,  however,  looser,  the  lobes  and  lobules  being  less  compactly 
arranged. 

Heidenhain  has  observed  that  the  alveolar  cells  in  the  pancreas  of  a  fasting 
dog  consist  of  two  zones,  an  inner  or  central  zone  which  is  finely  granular, 


Fig    266  — Section  of  the  Pancreas  of  Armadillo,  Showing  the  Two  Kinds  of  Gland-structure. 

(V.  D.  Harris.) 


and  which  stains  feebly,  and  a  smaller  parietal  zone  of  finely  striated  proto- 
plasm which  stains  easily.  The  nucleus  is  partly  in  one,  partly  in  the  other 
zone.  During  secretion  it  is  found  that  the  outer  zone  increases  in  size,  and 
the  central  granular  zone  diminishes,  as  in  the  case  of  the  salivary  glands. 
The  pancreatic  cell  itself  becomes  smaller  from  the  discharge  of  the  secretion. 
During  a  period  of  rest  the  granular  zone  again  increases  in  size  and  the 
outlines  of  the  cells  become  full  and  indistinct.  The  granules,  as  in  the  sali- 
vary cells,  are  the  material  from  which,  under  certain  conditions,  the  ferments 
of  the  gland  are  developed,  and  which  are  therefore  a  Zymogen.  In  addition  to 
the  ordinary  alveoli  of  the  pancreas  there  are  distributed  irregularly  in  the 
gland  other  collections  of  cells  of  a  different  character,  the  Islands  0}  Lan- 
gerhans.      These  cells  are    considerably  smaller,  their   protoplasm  is   more 


THE    PANCREAS 


-5iii5 


granular  and  less  easily  stained  with  hematoxylin,  and  their  nuclei  are  small 
and  stain  deeply.  The  collections  of  cells  vary  in  size  and  shape.  The 
special  form  of  nerve  terminations,  called  Pacinian  corpuscles,  are  often 
found  in  the  pancreas.  The  secretion  of  the  pancreas  has  been  obtained  for 
purposes  of  experiment  from  the  lower  animals  and  from  man  in  at  least 
one  case.     A   pancreatic  fistula   is  established  in    the    dog  by  opening  the 


Fig.  267. — Duct  with  Laterals  to  the  Alveoli.     Silver  method  of  Golgi  (E.  Muller).     A,  Duct 
with  branches;  m,  between  the  cells.     B,  Laterals  more  strongly  magnified. 


abdomen  and  exposing  the  duct  of  the  gland  which  is  then  made  to  com- 
municate with  the  exterior.  In  Pawlow's  method  a  circular  bit  of  the  intes- 
tinal mucous  membrane  around  the  mouth  of  the  duct  in  the  intestine  is 
brought  to  the  surface  and  stitched  into  the  wound.  The  secretion  is  then 
easily  collected  into  a  vessel  suspended  under  the  opening. 

The  Pancreatic  Juice.  Pancreatic  juice  is  colorless,  transparent, 
slightly  viscid,  and  alkaline  in  reaction.  It  varies  in  specific  gravity  from 
1010  to  1030,  according  as  it  is  obtained  from  a  permanent  fistula — then  more 


3f?4  FOOD     AND     DIGESTION 

watery,  or  from  a  newly  opened  duct.  The  solids  vary  in  a  temporary  fistula 
from  80  to  too  parts  per  thousand,  and  in  a  permanent  one  from  16  to  50  per 
thousand.  It  is  c  haracterized  by  having  three  distinct  and  important  en- 
zymes known  as  trypsin,  amylopsin,  and  steapsin,  whose  actions  are  respect- 
ively, proteolytic,  amylolytic,  and  lipolytic  (fat-splitting).  Maltase,  which 
inverts  the  disaccharides,  is  also  present,  and  some  have  stated  that  rennin  is 
found  in  pancreatic  juice. 

Chemical  Composition  of  Pancreatic  Juice.    (C.  Schmidt.) 

Recent  Permanent 

From  a  dog.  fistula.  fistula. 

Water 900.76  980.45 

Solids 99 .  24  19 .  55 

Organic  substances 90.44  12.71 

Ash 8.80  6.84 

Sodium  carbonate 0.58  3-31 

Sodium  chloride 7-35  2  -  5° 

Calcium,  magnesium,  and  sodium  phosphates °-53  0.08 

An  extract  of  pancreas  made  from  the  gland  which  has  been  re- 
moved from  an  animal  killed  during  digestion  possesses  the  active  properties 
of  pancreatic  secretion.  It  is  made  by  first  dehydrating  in  absolute  alcohol 
the  gland  which  has  been  cut  up  into  small  pieces.  After  the  entire  removal 
of  the  alcohol  the  gland  is  pulverized  and  extracted  in  strong  glycerin. 
The  amount  of  the  ferment  greatly  increases  if  the  gland  be  exposed  to  the 
air  for  three  or  four  hours  before  placing  in  alcohol;  indeed,  a  glycerin 
extract  made  from  the  gland  immediately  upon  the  removal  from  the  body 
often  appears  to  contain  none  of  the  ferments.  The  conversion  of  zymogen 
in  the  gland  into  the  ferment  takes  place  only  after  the  gland  stands  a  while. 
Dilute  acid  assists  or  accelerates  the  conversion,  and  if  a  recent  pancreas  be 
rubbed  up  with  dilute  acid  before  dehydration,  a  glycerin  extract  made 
afterward,  even  though  the  gland  may  have  been  only  recently  removed  from 
the  body,  is  very  active. 

Nervous  Regulation  of  the  Secretion  of  the  Pancreas.  Fibers  from 
the  vagus  and  from  the  splanchnics  are  distributed  to  the  pancreas.  In 
Pawlow's  laboratory  it  has  been  found  that  stimulation  of  these  nerves  leads 
to  the  increased  secretion  of  the  pancreas.  Popielski,  in  studying  the  effects 
of  dilute  hydrochloric  acid  solution  in  the  duodenum,  which  resulted  in  a 
marked  increase  of  pancreatic  secretion,  explained  the  phenomenon  as  a 
local  nerve  reflex. 

Doubt  has  been  cast  on  the  whole  question  of  nervous  control  by  the  recent 
discovery  of  the  fact  that  acid  (0.4  per  cent  hydrochloric  acid)  in  the  duodenum 
results  in  the  production  of  a  chemical  substance,  secretin,  by  the  duodenal 
mucous  membrane.  This  secretin  is  absorbed  into  the  circulation  and  acts 
specifically  on  the  pancreas  to  produce  increased  activity  by  the  pancreatic 
cells.     Acid  extracts  of  the  duodenal  mucous  membrane  produce  the  same 


ACTION    OF    THE    ENZYMES    OF    PANCREATIC    JUICE 


335 


effects  on  the  pancreas,  in  fact  this  is  the  current  method  of  stimulating 
the  flow  of  pancreatic  juice  at  the  present  time,  the  secretion  being  collected 
from  a  tube  introduced  into  the  duct 

Under  the  normal  stimulus  of  food,  the  flow  of  pancreatic  juice  is  greatly 
increased.  The  increase  continues  to  a  maximum  in  from  two  to  three  hours, 
after  which  it  gradually  decreases  through  the  period  of  digestion.     Pawlow 


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Fig.  268. — Three  Curves  Showing  the  Secretion  of  Pancreatic  Juice  upon  a  Diet  (1)  of  600  c.c. 
of  milk;  (2)  of  250  gm.  of  bread;  (3)  of  100  gm.  of  meat.  The  divisions  along  the  abscissa  repre- 
sent hours  after  the  beginning  of  the  meal;  the  figures  along  the  ordinates  represent  the  quantity 
of  the  secretion  in  cubic  centimeters.      (Walter.) 


has  found  a  certain  amount  of  adaptation  not  only  of  the  quantity  but  of 
the  enzyme  composition  of  the  pancreatic  secretion  to  the  kind  and  character 
of  the  food  (in  dogs). 

Action  of  the  Enzymes  of  Pancreatic  Juice.  The  secretion  of  the 
pancreas  accomplishes  its  digestive  action  by  means  of  the  enzymes  given 
above,  viz.,  trypsin,  amylopsin,  steapsin,  and  maltase. 

Trypsin.  Trypsin  is  a  proteolytic  enzyme.  Strange  to  say  it  does  not  exist 
in  the  fresh  pancreatic  juice  as  such,  but  makes  its  appearance  only  when  there 


330  FOOD      \M>     DIGESTION 

is  an  admixture  with  the  secretion  of  the  mucous  membrane  of  the  intestine. 
The  succus  entericus  contains  an  activating  enzyme,  enterokinase,  which 
converts  the  inactive  and  stable  trypsinogen  of  the  pancreatic  juice  into  the 
active  but  less  stable  trypsin.  This  fact  is  another  of  the  wonderful  series  of 
contributions  to  the  exact  knowledge  of  the  subject  of  digestion  made  from 
Pawlow's  laboratories. 

Trypsin  converts  proteids  into  proteoses  and  peptones.  The  process  is 
both  more  rapid  and  more  complete  than  in  gastric  digestion,  so  that,  in  the 
final  result,  the  peptones  are  greatly  in  excess  of  the  proteoses.  The  proteids 
pass  through  the  same  preliminary  stages  as  in  gastric  digestion,  being  split 
at  first  into  alkali-albumin,  then  into  primary  proteoses,  both  proto-proteose 
and  hetero-proteose,  and  then  into  deutero-proteose.  The  first  stages  are  so 
transient  that  it  is  difficult  to  detect  either  the  alkali-albumin  or  primary  pro- 
teose. The  deutero-albumoses  are  easily  demonstrated  in  the  earlier  stages, 
but  become  very  scanty  later.  Anti-albumid  is  found  as  a  side  product  in 
artificial  digestion,  but  is  not  present  in  normal  digestion. 

Trypsin  also  has  the  power  of  splitting  a  certain  proportion  of  peptones, 
the  hemi-peptones,  into  simpler  bodies  such  as  leucin  or  amido-caproic  acid, 
tyrosin  or  paraoxyphenyl-amido-propionic  acid,  lysin,  lysatinin,  tryptophan, 
and  some  other  bodies.  In  the  cleavage  of  the  proteid  molecule  there  is  prob- 
ably left  a  complex  nucleus  which  may  yet  serve  as  a  synthetic  center  for  the 
rebuilding  of  the  proteid  molecule.  This  nucleus  is  called  a  polype ptid. 
Leucin  and  tyrosin  have  been  found  in  the  intestinal  contents,  so  that  this 
destruction  of  hemipeptone  in  artificial  tryptic  digestion  must  take  place  to 
a  certain  extent  within  the  body  as  well. 

In  laboratory  experiments  only  about  one-half  of  the  peptones  can  be 
changed  in  this  way.  The  more  stable  portion  which  cannot  be  changed 
is  usually  known  as  antipeptone.  There  are  several  theories  as  to  the  reason 
or  use  of  this  change  into  leucin,  tyrosin,  etc.  One  of  the  most  plausible 
is  that  it  saves  the  body  from  needless  work  when  too  much  proteid  food  has 
been  taken;  the  breaking  down  in  the  intestine  of  bodies  only  slightly  removed 
from  urea  relieves  the  liver  and  other  glandular  organs  from  the  strain  of 
converting  an  excess  of  absorbed  proteid  material  into  a  form  in  which  it  can 
be  excreted.  Another  theory  is  that  leucin,  tyrosin,  etc.,  are  essential  for 
the  physiological  working  of  the  body  in  some  unknown  way,  just  as  are  the 
products  of  the  thyroid  gland.  The  formation  of  the  decomposition  products, 
indol  and  skatol,  is  caused  by  the  action  of  bacteria  on  proteids.  The  albu- 
minous or  proteid  substances  which  have  not  been  converted  into  peptone  in 
the  stomach,  and  the  partially  changed  substances,  i.e.,  the  proteoses,  are  con- 
verted into  peptone  by  the  pancreatic  juice,  and  then  in  part  into  leucin  and 
tyrosin,  etc. 

The  ferment  trypsin  acts  best  in  an  alkaline  medium,  but  will  act  also 
in  a  neutral  medium,  or  in  the  presence  of  a  small  amount  of  combined  acid; 


ACTION     OF    THE     ENZYMES     OF    PANCREATIC     JUICE  33? 

it  will  not  work  in  the  presence  of  free  acid.  It  therefore  differs  from  pepsin 
in  being  able  to  act  without  the  aid  of  any  other  substance  than  water.  In 
the  process  of  tryptic  digestion,  proteid  matter  does  not  swell  up  at  first,  but 
seems  to  be  corroded  at  once. 

Amylopsin.  Starch  is  converted  into  maltose  in  an  exactly  similar  manner 
to  that  which  happens  with  saliva,  erythro-dextrin  and  one  or  more  achroo- 
dextrins  being  the  intermediate  products.  The  amylolytic  enzyme  of  the 
pancreatic  juice,  which  cannot  be  distinguished  from  ptyalin,  is  called  amyl- 
opsin. The  maltose  thus  formed  is  converted  to  dextrose  by  the  maltase, 
in  which  form  it  is  ultimately  absorbed. 

Pancreatic  juice,  according  to  certain  observers,  possesses  the  property 
of  curdling  milk.  It  contains  a  special  ferment,  rennin,  for  that  purpose. 
The  ferment  is  distinct  from  trypsin,  and  will  act  in  the  presence  of  an  acid 
(W.  Roberts).  The  milk-curdling  ferment  of  the  pancreas  is,  in  some  pan- 
creatic extracts,  said  to  be  quite  powerful,  insomuch  that  i  c.c.  of  a  brine  ex- 
tract will  coagulate  50  c.c.  of  milk  in  a  minute  or  two. 

Steapsin  or  Lipase.  Oils  and  fats  are  emulsified  and  saponified  by  the  pan- 
creatic secretion.  The  terms  emulsification  and  saponification  may  need  a 
little  explanation.  The  former  is  used  to  signify  an  important  mechanical 
change  in  oils  or  fats,  whereby  they  are  made  into  an  emulsion,  or  in  other 
words  are  minutely  subdivided  into  small  particles.  If  a  small  drop  of  an 
emulsion  be  looked  at  under  the  microscope  it  will  be  seen  to  be  made  up  of 
an  immense  number  of  minute  rounded  particles  of  oil  or  fat,  of  varying 
sizes.  The  more  complete  the  emulsion  the  smaller  are  these  particles.  An 
emulsion  is  formed  at  once  if  oil  or  fat,  which  when  old  is  slightly  acid  from  the 
presence  of  free  fatty  acid,  is  mixed  with  an  alkaline  solution.  Saponification 
signifies  a  distinct  chemical  change  in  the  composition  of  oils  and  fats.  An 
oil  or  a  fat  being  made  up  chemically  of  glycerin,  a  triatomic  alcohol,  and 
one  or  more  fatty-acid  radicles,  when  an  alkali  (potassium  hydrate)  is  added 
to  it  and  heat  is  applied,  two  changes  take  place:  first,  the  oil  or  fat  is  split  up 
into  glycerin  and  its  corresponding  fatty  acid;  second  the  fatty  acid  combines 
with  the  alkali  to  form  a  soap  which  is  chemically  known  as  stearate,  oleate, 
or  palmitate  of  potassium.  Saponification  thus  means  a  chemical  splitting 
up  of  oils  or  fats  into  new  compounds,  and  emulsification  means  merely  a 
mechanical  splitting  up  into  minute  particles.  The  pancreatic  juice  has  been 
for  many  years  credited  with  the  possession  of  a  special  ferment,  which  was 
called  by  Claude  Bernard  steapsin,  and  which  is  a  lipase  or  fat-splitting  fer- 
ment. This  ferment  has  not  been  isolated,  but  its  presence  may  be  demon- 
strated by  adding  portions  of  the  fresh  pancreas  to  butter  or  other  fat  and 
maintaining  the  proper  temperature.  Its  action  is  made  manifest  by  the  libera- 
tion of  butyric  acid,  which  smells  like  rancid  butter. 

The  generally  accepted  theory  is  that  only  a  small  portion  of  the  fat  which 
is  eaten  is  thus  changed  into  soap,  and  that  the  function  of  the  saponified  fat 
22 


338 


FOOD     AND     DIGESTION 


is  to  assist  in  the  emulsification  of  the  major  part,  a  process  which  is  favorably 
influenced  by  the  bile.  The  proper  emulsification  of  fat  is  a  necessary  pre- 
liminary to  its  absorption,  for  when  in  disease  the  entrance  of  the  pancreatic 
juice  and  of  the  bile  to  the  intestine  is  interfered  with,  the  feces  contain  a 
great  excess  of  fat. 

Some  recent  experiments,  however,  tend  to  prove  that  the  entire  fat  of  the  food  is 
changed  in  the  intestine  into  fatty  acids  and  glycerin;  that  the  fatty  acids  are  entirely, 
or  in  part,  changed  to  soaps;  and  that  these  soaps,  or  mixture  of  soaps  and  free  fatty  acids, 
are  absorbed  in  solution.  The  chief  facts  favoring  this  view  are  that:  (i)  The  action  of 
steapsin  is  sufficiently  rapid  to  allow  the  saponification  of  a  full  fatly  meal  within  the 
ordinary  period  of  digestion;  (2)  histological  examination  has  never  shown  that  fat  par- 
licles  can  pass  into  a  columnar  cell,  and  none  have  ever  been  found  in  the  broad  striated 
border  of  the  cell;  (3)  the  fat  globules  found  in  columnar  cells  after  a  fatty  meal  grow 
steadily  larger  as  the  period  of  absorption  progresses,  indicating  that  they  are  deposited 
from  solution;  (4^  the  fatty  acids  are  easily  soluble  in  bile  solutions,  and  the  solubility  of 
the  soaps  is  greatly  increased  by  the  presence  of  bile.  The  fat  constituents,  according  to 
this  theory,  are  recombined  in  the  columnar  cells  to  form  neutral  fats. 

Conditions  which  Influence  the  Action  of  the  Pancreatic  Enzymes. 

The  various  pancreatic  enzymes  are  influenced  by  heat,  by  the  presence  of 
an  excess  of  digestion  products,  etc.,  in  the  same  way  as  ptyalin  and  pepsin. 
Pancreatic  enzymes  act  in  a  neutral  but  best  in  an  alkaline  solution.  The 
trypsin,  strange  to  say,  is  quickly  destroyed  by  the  alkaline  solution  (Bayliss 
and  Starling).  The  pancreatic  juice  offers  the  special  case  of  a  secretion  of 
proenzyme  which  is  stable  in  alkaline  solution  until  acted  on  by  enterokinase, 
and  the  amount  of  kinase  present  will,  therefore,  markedly  influence  the 
amount  of  digestion  of  proteid  per  unit  of  time. 

The  Secretions  of  the  Liver.  The  liver,  the  largest  gland  in  the 
body,  situated  in  the  abdomen  on  the  right  side  chiefly,  is  an  extremely  vascu- 
lar organ,  and  receives  its  supply  of  blood  from  two  distinct  sources,  viz., 


Fig.  269.— The  Liver  from  Below  and  Behind.  L.  S.,  Spigelian  lobe;  L.  C,  caudate  lobe; 
L.  Q.,  quadrate  lobe;  R.  L.,  right  lobe;  L.L.,  left  lobe;  g.  bl.,  gall-bladder;  v.c.i.,  inferior  vena 
cava;  u.f.,  umbilical  fissure;  f.d.v.,  fissure  of  the  ductus  venosus;  p,  portal  fissure  with  portal  vein, 
hepatic  artery  and  bile-duct.      (Wesley,  from  a  His  model  ) 


STRUCTURE     OF    THE    LIVER 


339 


from  the  portal  vein  and  from  the  hepatic  artery,  while  the  blood  is  returned 
from  it  into  the  vena  cava  inferior  by  the  hepatic  veins.  Its  secretion,  the  bile, 
is  conveyed  from  it  by  the  hepatic  duct,  either  directly  into  the  intestine,  or, 
when  digestion  is  not  going  on,  into  the  cystic  duct,  and  thence  into  the  gall- 


Fig.  270. — Portion  of  a  Lobule  of  Liver,     a.  Bile  capillaries  between  liver  cells,  the  network  in 
which  is  well  seen;   b,  blood  capillaries.      X  350.      (Klein  and  Noble  Smith.) 

bladder,  where  it  accumulates  until  required.  The  portal  vein,  hepatic  artery, 
and  hepatic  duct  branch  together  throughout  the  liver,  while  the  hepatic  veins 
and  their  tributaries  run  by  themselves.  The  interstices  of  these  vessels  are 
filled  by  the  liver  cells. 

Structure  of  the  Liver.     The  liver  is  made  up  of  small  roundish 
or  oval  portions  called  lobules,  each  of  which  is  about  ^V  of  an  mcn  (about 


Fig.  271. — Hepatic  Cells  and  Bile  Capillaries,  from  the  Liver  of  a  Child  Three  Months  Old. 
Both  figures  represent  fragments  of  a  section  carried  through  the  periphery  of  a  lobule.  The  red 
corpuscles  of  the  blood  are  recognized  by  their  circular  contour;  vp,  corresponds  to  an  interlobular 
vein  in  immediate  proximity  with  which  are  the  epithelial  cells  of  the  biliary  ducts.      (E.  Hering.) 

i  mm.)  in  diameter,  and  includes  the  minute  hepatic  artery  and  hepatic 
duct.  The  hepatic  cells,  which  form  the  glandular  or  secreting  part  of  the 
liver,  are  of  spheroidal  form,  somewhat  polygonal  from  mutual  pressure,  about 


340 


FOOD     AND     DIGESTION 


25  to  30  ft  in  diameter,  and  possess  one,  sometimes  two  nuclei.  The  cell-sub- 
stance contains  a  variable  amount  of  glycogen  and  often  some  fatty  molecules, 
and  possibly  some  granules  of  bile  pigment. 

The  bile  capillaries  commence  between  the  hepatic  cells,  and  are  bounded 
by  a  delicate  membranous  wall  of  their  own.     They  appear  to  be  always 


K>    V   Ml 

Fig.  272. — Section  of  Liver.      X  80.     P,  Portal  vein;  H,  hepatic  artery;   B,  bile-duct.     (Hen 

cirickson.) 


bounded  by  hepatic  cells  on  all  sides,  and  are  thus  separated  from  the  nearest 
blood  capillary  by  at  least  the  breadth  of  one  cell,  figures  271  and  272. 

The  gall-bladder,  g.  bl,  figure  269,  is  a  pyriform  sac  attached  to  the  under 
surface  of  the  liver,  and  supported  also  by  the  peritoneum.  The  larger  end, 
or  fundus,  projects  beyond  the  front  margin  of  the  liver,  while  the  smaller 
end  contracts  into  the  cystic  duct.  It  is  a  muscular  walled  reservoir  covered 
with  a  serous  epithelium  and  lined  by  mucous  membrane.  The  function 
of  the  gall-bladder  is  to  retain  the  bile  during  the  interval  of  digestion. 

The  Bile.  The  bile  is  a  somewhat  viscid  fluid,  of  a  yellow,  reddish- 
yellow,  or  green  color,  a  strongly  bitter  taste,  and,  when  fresh,  with  a  scarcely 
perceptible  odor;  it  has  a  neutral  or  slightly  alkaline  reaction,  and  its  specific 
gravity  is  about  1020.    Its  color  and  consistency  vary  much,  quite  independent 


THE     BILE  341 

of  disease;  but,  as  a  rule,  bile  becomes  gradually  more  deeply  colored  and 
thicker  as  it  advances  along  its  ducts,  or  when  it  remains  long  in  the  gall- 
bladder where  it  becomes  more  viscid  and  ropy,  darker,  and  more  bitter.  This 
is  on  account  of  its  greater  degree  of  concentration,  from  resorption  of  its 
water,  and  also  from  being  mixed  with  mucus. 

Chemical  Composition  of  Human  Bile.     (Frerichs.) 

Water 859 . 2 

Solids — Bile  salts 9 1  -  5 

Fat g .  2 

Cholesterin 2.6 

Mucus  and  coloring  matters 29 . 8 

Salts 7.7 

140.8 


Bile  sails  can  be  obtained  as  colorless,  exceedingly  deliquescent  crystals, 
soluble  in  water,  alcohol,  and  alkaline  solutions,  giving  to  the  watery  solution 
the  taste  and  general  characters  of  bile.  They  consist  of  sodium  salts  of  gly- 
cocholicand  taurocholic  acids;  the  formula  of  the  former  being  C„H„NaNO  , 

o       26      42  6 

and  of  the  latter  C26H44NaN07S. 

The  bile  acids  are  easily  decomposed  by  the  action  of  dilute  acids  or  alkalies  thus: 

C26H43N06  +  H20  =  C2H5NO2  +  C24H4„05 

Glycocholic  Acid.  Glycin.  Cholic  Acid. 

and  C2CH45NO,S  +  H20  =  C2H,N03S  +  C24H40Os 
Taurocholic  Acid.  Taurin.  Cholic  Acid. 

Glycin  is  amido-acetic  acid,  i.e.,  acetic  acid  C2H402,  with  one  of  the  atoms  of  H  re- 
placed by  the  radical  amidogen  NH2C2H3(NH2)02,  C2H5NO2.  Taurin  likewise  is 
amido-isethionic  acid.  Isethionic  acid  is  sulphurous  acid  H2SO3,  in  which  an  atom  of 
H  is  replaced  by  the  monatomic  radicle  oxy-ethylene,  C2H4OH,  viz.,  H(C2H40H)SOi; 
and  in  amido-isethionic  acid,  the  OH  hydroxyl  in  this  radicle  is  replaced  by  amidogen  NH», 
thus  H(C2H4NH2)S03  =  C2H7NSO3.  The  proportion  of  these  two  salts  in  the  bile  of 
different  animals  varies,  e.g.,  in  the  ox  bile  the  glycocholate  is  in  great  excess,  whereas  the 
bile  of  the  dog,  cat,  bear,  and  other  carnivora  contains  taurocholate  alone.  In  human  bile 
the  glycocholate  is  in  excess  (4.8  to  1.5). 

The  yellow  coloring  matter  of  the  bile  of  man  and  the  Carnivora  is  termed 
Bilirubin,  Clt}H18N203,  is  crystallizable  and  insoluble  in  water,  and  soluble  in 
chloroform  or  carbon  disulphide.  A  green  coloring  matter,  Biliverdin,  C1BH  - 
N204,  which  always  exists  in  large  amount  in  the  bile  of  Herbivora,  is  formed 
from  bilirubin  on  exposure  to  the  air,  or  by  subjecting  the  bile  to  any  other 
oxidizing  agency,  as  by  adding  nitrous  acid.  Biliverdin  is  soluble  in  alcohol, 
glacial  acetic  acid,  and  strong  sulphuric  acid,  but  insoluble  in  water,  in  chloro- 
form, and  ether.  It  is  usually  amorphous,  but  may  sometimes  crystallize  in 
green  rhombic  plates. 

There  is  a  close  relationship  between  the  coloring  matters  of  the  blood 
and  of  the  bile,  and  it  may  be  added,  between  these  and  that  of  the  urine, 


342  FOOD     AND     DIGESTION 

urobilin,  and  of  the  feces,  stcrcobilin.  It  is  probable  they  are,  all  of  them, 
varieties  of  the  same  pigment,  or  derived  from  the  same  source.  Cholesterin, 
C,7H45OH,  and  lecithin,  C42Hs4NP09  are  constant  constituents  of  bile.  Iron 
is  found  among  the  salts  of  the  ash. 


Fig.  273. — Crystalline  Scales  of  Cholesterin. 

The  Role  of  Bile  in  Intestinal  Digestion.  Though  it  is  not  a  true 
digestive  fluid,  in  that  it  has  no  ferment  and  digests  nothing  itself,  yet  it  must 
be  regarded  as  an  important  aid  to  digestion  for  the  following  reasons:  (a)  Bile 
assists  in  emulsifying  the  fats  of  the  food,  and  thus  renders  them  capable  of 
passing  into  the  lacteals  by  absorption.  For  it  has  appeared  in  some  experi- 
ments in  which  the  common  bile-duct  was  tied,  that,  although  the  process 
of  digestion  in  the  stomach  was  unaffected,  chyle  was  no  longer  well  formed; 
the  contents  of  the  lacteals  consisting  of  clear,  colorless  fluid,  instead  of  being 
opaque  and  white,  as  they  ordinarily  are  after  feeding.  It  is,  however,  the 
combined  action  of  the  bile  with  the  pancreatic  juice  to  which  the  emulsifica- 
tion  is  due  rather  than  to  that  of  the  bile  alone.  The  bile  itself  has  a  very 
feeble  emulsifying  power.  If  the  theory  be  accepted  that  fats  are  absorbed 
as  fatty  acids  and  soaps,  in  solution,  the  action  of  the  bile  becomes  very  im- 
portant because  solutions  of  bile  salts  have  the  power  of  dissolving  the  fatty 
acids.  The  moistening  of  the  mucous  membrane  of  the  intestines  with  bile, 
for  this  very  reason,  facilitates  absorption  of  fatty  matters  through  it. 

(b)  The  bile,  like  the  gastric  fluid,  has  a  certain  but  not  very  considerable 
antiseptic  power,  and  may  serve  to  prevent  the  decomposition  of  food  during 
the  time  of  its  sojourn  in  the  intestines.  Experiments  show  that  the  contents 
of  the  intestines  are  much  more  fetid  after  the  common  bile-duct  has  been 
tied  than  at  other  times.  Moreover,  it  is  found  that  the  mixture  of  bile  with 
a  fermenting  fluid  stops  the  process  of  fermentation. 

Bile  is  also  an  excretive  fluid  carrying  waste  products  thrown  off  by  the 
liver.  The  liver  during  fetal  life  is  proportionately  larger  than  it  is  after 
birth,  and  the  secretion  of  bile  is  active,  although  there  is  no  food  in  the  in- 
testinal canal  upon  which  it  can  exercise  any  digestive  property.     At  birth, 


MODE     OF    SECRETION    AND     DISCHARGE     OF     BILE  343 

the  intestinal  canal  is  full  of  concentrated  bile,  mixed  with  intestinal  secretion, 
and  this  constitutes  the  meconium,  or  feces  of  the  fetus.  In  the  fetus,  therefore, 
the  main  purpose  of  the  secretion  of  bile  must  be  directly  excretive.  Probably 
all  the  bile  secreted  in  fetal  life  is  incorporated  in  the  meconium,  and  with  it 
discharged. 

Mode  of  Secretion  and  Discharge  of  Bile.  The  secretion  of  bile 
is  continually  going  on,  but  is  retarded  during  fasting,  and  accelerated  on 
taking  food.  This  is  shown  by  tying  the  common  bile-duct  of  a  dog,  and  estab- 
lishing a  fistulous  opening  between  the  skin  and  gall-bladder,  whereby  all  the 
bile  secreted  is  discharged  at  the  surface.  When  the  animal  is  fasting,  some- 
times not  a  drop  of  bile  is  discharged  for  several  hours.  In  about  ten  minutes 
after  the  introduction  of  food  into  the  stomach,  the  bile  begins  to  flow  abun- 
dantly, and  continues  to  do  so  during  the  period  of  digestion. 

The  bile  is  constantly  being  formed  in  the  hepatic  cells;  thence,  being  dis- 
charged into  the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks,  and 
from  the  main  hepatic  duct  may  be  carried  at  once  into  the  duodenum.  This 
probably  happens  only  while  digestion  is  going  on,  i.e.,  for  five  to  seven  hours 
after  the  introduction  of  food  into  the  stomach.  During  fasting,  it  flows  from 
the  common  bile-duct  through  the  cystic  duct  into  the  gall-bladder,  where  it 
accumulates  till,  in  the  next  period  of  digestion,  it  is  discharged  into  the  intes- 
tine. The  gall-bladder  thus  acts  as  a  reservoir  for  the  bile  during  the  intervals 
when  digestion  is  not  in  progress. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder  is  simple. 
The  orifice  through  which  the  common  bile-duct  communicates  with  the 
duodenum  is  narrower  than  the  duct,  and  appears  to  be  closed,  except  when 


Fir,.  274. — Transverse  Section  through  Four  Crypts  of  Lieberkiihn,  from  the  Large  Intestine 
of  the  Pig.  They  are  lined  by  columnar  epithelial  cells,  the  nuclei  being  placed  in  the  outer  part 
of  the  cells.  The  divisions  between  the  cells  are  seen  as  lines  radiating  from  l,  the  lumen  of  the 
crypt;  g,  epithelial  cells,  which  have  become  transformed  into  goblet  cells.  X  350.  (Klein  and 
Noble  Smith.) 

there  is  sufficient  pressure  behind  to  force  the  bile  through  it.  The  pressure 
exercised  upon  the  bile  secreted  during  the  intervals  between  periods  of  diges- 
tion appears  insufficient  to  overcome  the  force  of  the  sphincter  by  which  the 
orifice  of  the  duct  is  closed;  and  the  bile  in  the  common  duct  traverses  the 


344 


FOOD     AM)     DIGESTION 


cystic  duct  and  so  passes  into  the  gall-bladder,  being  probably  aided  in  this 
retrograde  course  by  the  peristaltic  action  of  the  ducts.  The  bile  is  discharged 
from  the  gall-bladder  and  enters  the  duodenum  on  the  introduction  of  food 
into  the  small  intestine.  It  is  pressed  on  by  the  contraction  of  the  coats  of 
the  gall-bladder,  and  of  the  common  bile-duct.  Their  contraction  is  excited 
by  the  stimulus  of  the  food  in  the  duodenum  acting  through  a  reflex  arc  to 
produce  contractions,  the  force  of  which  is  sufficient  to  open  the  orifice  of  the 
common  bile-duct. 

When  the  discharge  of  the  bile  into  the  intestine  is  prevented  by  an  ob- 
struction of  some  kind,  as  by  a  gall-stone  blocking  the  hepatic  duct,  it  is  reab- 


Fig.  275. — Longitudinal  Section  of  Fundus  of  Crypt  of  Lieberkiihn.  b.  Goblet  cell  showing 
mitosis;  e,  epithelial  cell;  k,  cell  of  Paneth;  /,  leucocyte  in  epithelium;  m,  mitosis  in  epithelial  cell. 
Surrounding  the  crypt  is  seen  the  stroma  of  the  mucous  membrane.      X  530.      (Kolliker.) 


sorbed  in  great  excess  into  the  blood,  and,  circulating  with  it,  gives  rise  to 
the  well-known  phenomena  of  jaundice.  This  is  explained  by  the  fact  that  the 
pressure  of  secretion  in  the  ducts,  although  normally  very  low,  not  exceeding 
15  millimeters  of  mercury  in  the  dog,  is  still  higher  than  that  of  the  portal 
veins.  If  the  pressure  exceeds  15  mm.  the  secretion  continues  to  be  formed 
but  passes  into  the  blood-vessels  through  the  lymphatics. 

The  Intestinal  Secretion,  or  Succus  Entericus.  It  is  impossible  to 
isolate  the  secretion  of  the  glands  of  Brunner  or  of  the  glands  of  Lieberkiihn, 
but  the  total  secretion  of  the  intestinal  mucosa  can  be  secured  by  isolating  a 
loop  of  intestine  by  the  operation  known  as  the  Thiry  fistula.    A  few  drops 


DIGESTIVE     CHANGES     IN     THE     SMALL     INTESTINE  34,5 

of  secretion,  the  succus  entericus,  can  be  obtained  by  this  means.  Intestinal 
juice  is  a  yellowish  alkaline  fluid  with  a  specific  gravity  of  ion  and  con- 
tains about  2.5  per  cent  of  solid  matters. 

Intestinal  juice  has  only  slight  digestive  action.  It  contains  a  weak  pro- 
teolytic enzyme  and  a  weak  amylolytic  enzyme.  Maltase  is  also  present.  But 
the  chief  and  most  profound  importance  is  given  to  the  intestinal  juice  by  the 
discovery  of  the  activating  enzyme,  enterokinase.  This  specific  activating 
enzyme  for  the  tripsinogen  of  the  pancreatic  juice  places  the  intestinal  secre- 
tion in  the  rank  of  necessary  secretion  for  efficient  digestion.  Enterokinase 
can  be  prepared  by  extracting  the  superficial  scrapings  of  the  intestinal  mucous 
coat.  The  duodenal  region  is  richest  in  enterokinase,  but  the  secretion  of  the 
lower  intestinal  lengths  also  contains  the  enzyme. 

Extracts  of  the  mucosa  of  the  intestine  have  been  found  to  contain  another 
substance  which  has  the  specific  action  of  splitting  peptones  into  simpler 
amino  bodies.    This  substance  has  been  called  erepsin. 

There  are,  therefore,  three  important  new  substances  in  the  succus  en- 
tericus (or  in  the  extract  of  the  glands),  secretin,  erepsin,  and  enterokinase, 
in  addition  to  the  proteolytic  and  diastatic  enzymes. 

Summary  of  the  Digestive  Changes  in  the  Small  Intestine.  The 
thin  chyme  which,  during  the  whole  period  of  gastric  digestion,  is  being  con- 
stantly squeezed  or  strained  through  the  pyloric  orifice  into  the  duodenum, 
consists  of  albuminous  matter  that  is  broken  down,  dissolving  and  half  dis- 
solved; of  fatty  matter  broken  down  and  melted,  but  not  dissolved  at  all; 
of  starch  in  various  stages  of  the  process  of  conversion  into  sugar,  and  as 
it  becomes  sugar  dissolving  in  the  fluids  with  which  it  is  mixed;  while  with 
these  are  mingled  gastric  juice  and  fluid  that  has  been  swallowed,  together 
with  such  portions  of  the  food  as  are  not  digestible. 

The  chyme  in  the  duodenum  is  subjected  to  the  influence  of  the  bile  and 
pancreatic  juice  and  also  to  that  of  the  succus  entericus.  All  these  secretions 
have  a  more  or  less  alkaline  reaction,  and  neutralize  the  acid  of  the  gastric 
chyme. 

The  special  digestive  changes  in  the  small  intestine  are:  (i)  The  fats  are 
changed  by  the  bile  and  pancreatic  juice  in  two  ways,  (a)  They  are  chemically 
decomposed  by  the  alkaline  secretions,  and  a  soap  and  glycerin  are  the  result. 
(b)  They  are  emulsified,  i.e.,  their  particles  are  minutely  subdivided  and  dif- 
fused, so  that  the  mixture  assumes  the  condition  of  a  milky  fluid  or  emulsion. 
(2)  The  albuminous  substances  which  have  been  partly  dissolved  in  the  stomach 
are  subjected  chiefly  to  the  action  of  the  pancreatic  juice.  The  pepsin  is 
rendered  inert  by  the  bile.  The  pancreatic  trypsin  proceeds  with  the  fur- 
ther conversion  of  the  proteoses  into  peptones,  and  part  of  the  peptones 
(hemipeptones)  into  leucin,  tyrosin,  and  other  amino  bodies.  (3)  The  starchy 
portions  of  the  food  are  now  acted  on  briskly  by  the  pancreatic  juice  and 
the  succus  entericus,  and  are  changed  to  maltose  and  dextrose.     (4)  Salines 


346 


FOOD     AND     DIGESTION 


and  other  soluble  matters,  such  as  common  salt,  are  usually  in  a  state  of 
solution  before  they  reach  the  intestine. 

Digestive  Changes  in  the  Large  Intestine.  The  changes  which  take 
place  in  the  chyme  in  the  large  intestine  are  probably  only  the  continuation 
of  the  same  changes  that  occur  in  the  course  of  the  food's  passage  through 
the  upper  part  of  the  intestinal  canal.  No  special  enzymes  have  been  clearly 
shown  for  the  mucous  membrane  of  the  large  intestine.  The  enzymes  of  the 
small  intestine  may  continue  their  action  here,  being  hindered  only  by  the 
acid  developed  from  fermentation  processes. 

Action  of  Micro-organisms  in  the  Intestines.  Certain  changes 
take  place  in  the  intestinal  contents  independent  of,  or  at  any  rate  supple- 
mental to,  the  action  of  the  digestive  ferments.  These  changes  are  brought 
about  by  the  action  of  micro-organisms  or  bacteria.  We  have  indicated  else- 
where that  the  digestive  ferments  are  examples  of  unorganized  ferments,  so 
bacteria  are  examples  of  organized  ferments.     Organized  ferments,  of  which 


°o-o00o° 


»       0 

0  <p 


V 


YU 


7 


d? 


s 


Fig.  276. — Types  of  Micro-organisms,  a,  Micrococci  arranged  singly;  in  twos,  diplococci — 
if  all  the  micrococci  at  a  were  grouped  together,  they  would  be  called  staphylococci — and  in  fours, 
sarcinse;  b,  micrococci  in  chains,  streptococci;  c,  and  d,  bacilli  of  various  kinds,  one  is  represented 
with  flagellum;  e,  various  forms  of  spirilla;  /,  spores,  either  free  or  in  bacilli. 


the  yeast  plant  may  be  taken  as  a  typical  example,  consist  of  unicellular  vege- 
table organisms,  which  when  introduced  into  a  suitable  medium  grow  with  re- 
markable rapidity.  By  their  growth  they  produce  new  substances  from  those 
supplied  to  them  as  food.  Thus,  for  example,  when  the  yeast  cell  is  introduced 
into  a  solution  of  grape-sugar,  it  grows,  and  alcohol  and  carbon  dioxide  are 
produced.  These  substances  probably  arise  from  the  formation  by  the  cell  ac- 
tivity of  some  chemical  substances  which  are  allied  to  the  unorganized  ferments 
and  which  greatly  increase  in  amount  with  the  multiplication  of  the  original 
cell.  In  all  such  fermentative  processes  organisms  analogous  to  the  yeast  cell 
are  present,  and  it  is  not  strange  that  if  the  ferment  cell  is  introduced  into  a 
suitable  medium  it  may  by  its  rapid  growth  convert  an  unlimited  amount  of 
one  substance  into  another.  Speaking  generally,  a  special  variety  of  cell  is 
concerned  with  each  ferment  action,  thus  one  variety  has  to  do  with  alcoholic, 
another  with  lactic,  and  another  with  acetous  fermentation. 


THE     FECES  347 

A  considerable  number  of  species  of  bacteria  exist  in  the  body  during  life, 
chiefly  in  connection  with  the  mucous  membranes,  particularly  of  the  digestive 
tract.  Many  forms  of  bacteria  have  been  isolated  from  the  mouth,  a  few 
varieties  from  the  stomach,  and  a  very  large  number  from  the  intestines.  It 
is  only  in  the  last-named  locality  that  their  multiplication  has  much  effect  from 
a  physiological  point  of  view.  The  normal  (hydrochloric-acid)  acidity  of  the 
stomach  usually  destroys  all  the  micro-organisms  taken  in  with  the  food,  but 
when  the  amount  of  this  acid  is  deficient  (and  sometimes  even  when  it  is  nor- 
mal) some  of  the  spores  may  escape.  On  reaching  the  small  intestine  these 
spores  begin  to  develop  in  its  alkaline  medium,  and  may  increase  to  such  an 
extent  as  to  stop  all  intestinal  digestion;  the  point  where  this  occurs  varies 
from  day  to  day.  The  large  intestine  always  swarms  with  micro-organisms, 
though  they  do  not  readily  pass  the  ileo-cecal  valve  into  the  small  intestine. 
The  bacteria  found  in  the  intestine  are  anaerobic,  i.e.,  they  do  not  develop  in 
the  presence  of  free  oxygen. 

The  changes  induced  in  the  intestine  by  the  activity  of  micro-organisms 
are  of  two  kinds,  fermentation  and  putrefaction;  the  former  of  these  results 
in  the  breaking  down  of  carbohydrate  matter,  and  the  latter  in  the  disintegra- 
tion of  proteid  matter.  The  process  of  fermentation  is  the  less  complex  and 
probably  occurs  normally  in  the  small  intestine  to  a  certain  extent.  The  lactic- 
acid  fermentation  is  the  most  important,  though  the  butyric-acid  fermentation 
is  next;  under  their  influence  the  carbohydrates  are  broken  down  into  lactic 
and  butyric  acids,  and  perhaps  into  acetic  acid  also.  Carbonic  acid  gas  may 
be  formed  at  the  same  time  and  cause  flatulence.  Cellulose  and  other  in- 
soluble carbohydrates  are  decomposed,  with  the  formation  of  marsh  gas 
and  hydrogen,  which  escape  by  the  rectum. 

In  putrefaction  the  process  is  similar  to  that  in  tryptic  digestion,  the  pro- 
teids  being  broken  down  into  peptones,  leucin,  tyrosin,  and  a  long  row  of  similar 
substances.  It  also  results  in  the  production  of  various  gases,  such  as  carbon 
dioxide,  sulphureted  hydrogen,  ammonia,  hydrogen  and  methane  (marsh 
gas),  and  of  a  high  percentage  of  the  volatile  fatty  acids,  valerianic  and  butyric. 
Of  the  aromatic  substances  the  most  important  are  indol  and  skatol,  though 
their  toxicity  has  been  greatly  overestimated.  Some  undergo  oxidation,  indol 
and  skatol  forming  indoxyl  and  skatoxyl;  they  are  usually  carried  off  in  the 
feces,  but  when  the  bowel  is  obstructed  they  are  absorbed  and  eventually 
appear  in  the  urine,  indoxyl  and  skatoxyl  forming  respectively  indoxyl-  and 
skatoxyl-sulphuric  acids  and  their  salts.  Tyrosin  is  further  broken  down 
into  para-oxy-phenol-propionic  acid,  paracresol,  and  phenol;  para-oxy-phenol- 
acetic  acid  is  also  formed.  Experiments  have  been  performed  to  determine 
whether  or  not  the  intestinal  bacteria  are  neccessary  to  normal  digestion.  The 
weight  of  evidence  is  in  favor  of  the  view  that  they  are  not. 

The  Feces.  The  contents  of  the  large  intestine,  as  they  proceed 
toward  the  rectum,  become  more  and  more  solid,  lose  more  liquid  and  nutrient 


348 


FOOD    AND     DIGESTION 


parts,  and  gradually  acquire  the  odor  and  consistency  characteristic  of  feces. 
After  a  sojourn  of  uncertain  duration  in  the  sigmoid  flexure  of  the  colon,  or 
in  the  rectum,  they  are  finally  expelled  by  the  act  of  defecation.  The  average 
quantity  of  solid  matter  evacuated  by  the  human  adult  in  twenty-four  hours 
is  about  200  to  250  grams,  but  the  amount  and  character  vary  exceedingly  ac- 
cording to  the  food  eaten.  Vegetable  foods  contain  much  indigestible  matter, 
while  meats  and  meat  diets  leave  very  little  unabsorbed  material  to  be  ex- 
pelled in  the  feces. 


Table  of  Composition  of  Feces. 

The  amount  of  water  varies  considerably,  from  68  to  82  per  cent   and 
upward.     The  following  table  gives  about  an  average  composition: 

Water 733 .  00 

Solids,  comprising: 

a.  Insoluble  residues  of  the  food,  uncooked  starch,  cellulose, 

woody  fibers,  cartilage,  horny  matter,  mucin,  seldom  mus- 
cular fibers  and  other  proteids,  fat,  and  cholesterin 

b.  Certain  substances  resulting  from  decomposition  of  foods, 

indol,  skatol,  fatty  and  other  acids;    calcium  and  mag- 
nesium soaps  

c.  Special  excretions, — Excretin,  excretoleic  acid   (Marcet), 

and  stercorin  (Austin  Flint) 

d.  Salts, — Chiefly  phosphate  of  magnesium  and  phosphate 

of  calcium,  with  small  quantities  of  iron,  soda,  lime,  and 
silica 

e.  Insoluble  substances  accidentally  introduced  with  the  food 

f.  Mucus,  epithelium,  altered  coloring  matter  of  bile,  fatty 

acids,  etc 

g.  Varying  quantities  of  other  constituents  of  bile  and  secre- 

tions   


267.00 


Intestinal  Gases.     Under  ordinary  circumstances,  the  alimentary  ca- 
nal contains  a  considerable  quantity  of  gases.    The  presence  of  gas  in  the 


t 


4     ^hOOCx^cD 


z 

5    A 


Fig.  277. — Diagram  Illustrating  the  Segmentation  of  the  Food  in  the  Small  Intestine.     (Cannon.) 


intestines  is  so  constant  and  the  amount  in  health  so  uniform  that  there  can 
be  no  doubt  that  its  existence  is  a  normal  condition. 

The  gas  contained  in  the  stomach  and  bowels  is  from  air  swallowed  with 


MOVEMENTS     OF    THE     INTESTINES 


349 


either  food  or  saliva,  gases  developed  by  the  decomposition  of  foods,  or  of  the 
secretions  and  excretions  thrown  into  the  intestines.  The  decomposition  of 
foods  is  the  chief  source.  The  following  table,  compiled  by  Brinton,  is  a  col- 
lection of  analyses  that  have  been  made  and  is  chiefly  valuable  as  showing 
the  kinds  of  gases  present: 


Gases  Found  in  the  Alimentary  Canal. 


Composition  by  Volume. 

Whence  obtained. 

Oxygen. 

Nitrog. 

Carbon. 
Acid. 

Hydrog. 

Carburet. 
Hydrogen. 

Sulphuret. 
Hydrogen. 

Stomach 

II 

71 
32 
67 

35 
46 
22 

14 

3° 
12 

51 
43 
40 

4 

38 

8 

6 

19 

13 

8 

11 

19 

Small   intestines 

1 

Colon 

)■   Trace. 

Rectum 

J 
o-5 

Expelled  per  anum. .  .  . 

The  amounts  of  the  gases  vary  with  the  diet. 

An  analysis  of  the  intestinal  gases  (Ruge,  copied  by  Halliburton)  in  man 
is  as  follows: 


Gases. 


Carbon  dioxide 

Hydrogen 

Carbureted  hydrogen 
Nitrogen 


Milk  Diet. 


0    to  16 
43  to  54 
0.9 
36  to  38 


Meat  Diet. 


0.7 
26 
45 


to  13 

to   3 

to  37 
to  64 


Vegetable   Diet. 


44 


to  34 

■5  to     4 

to  55 

to  19 


The  carbon  dioxide  arises  from  the  carbonates  and  lactates  in  food,  from 
fermentation  and  putrefaction  of  carbohydrates  and  proteids,  and  from 
butyric-acid  fermentation. 

The  hydrogen  is  derived  from  butyric-  and  lactic-acid  fermentations,  and 
carbureted  hydrogen  comes  from  the  decomposition  of  acetates  and  lactates 
and  from  cellulose.    The  nitrogen  is  derived  from  the  swallowed  air. 


MOVEMENTS  OF  THE  INTESTINES. 

The  muscular  activity  of  the  intestines  accomplishes  two  important  func- 
tions, i.e.,  it  thoroughly  mixes  the  digesting  food  and  secretions  and  it  carries 
the  content  along  the  tract.  Intestinal  peristalses  have  been  described  for  a 
long  time.  These  peristalses  begin  as  contractions  of  the  circular  muscles, 
producing  ring-like  constrictions  that  are  propagated  as  waves  over  the  intestine 


350  FOOD     AND     DIGESTION 

from  above  downward.  Such  constrictions  carry  the  intestinal  contents 
forward.  The  longitudinal  muscles  by  their  contraction  produce  pendular 
motion  of  the  intestine. 

A  most  instructive  contribution  to  the  knowledge  of  intestinal  movements 
has  been  made  by  Cannon.  He  fed  cats  food  mixed  with  10  to  33  per  cent  of 
subnitrate  of  bismuth,  and  observed  the  shadows  of  the  food  when  subjected 
to  the  Roentgen  rays.  A  length  of  food  in  the  intestine  was  seen  to  be  con- 
stricted into  a  series  of  oval  masses,  figure  277.  Each  of  these  oval  masses  is 
quickly  constricted  in  the  middle,  and  neighboring  halves  of  adjacent  masses 
flow  together.  After  this  process  is  repeated  a  number  of  times  a  peristaltic- 
wave  of  the  type  previously  described  sweeps  the  whole  content  of  the  loop 
down  the  intestinal  tract. 

Peristaltic  contractions  of  the  same  general  type  as  in  the  small  intestine 
also  occur  in  the  large  intestine.  Cannon  has  noted  a  variation  here,  also.  The 
ascending  and  the  transverse  loops  of  the  colon  exhibit  rhythmic  antiperistalses 
which  keep  the  content  moving  against  the  ileocecal  valve  for  several  minutes 
at  a  time.  From  time  to  time  strong  general  contractions,  in  the  cecum  and 
ascending  colon,  force  some  of  the  food  onward.  When  material  has  accumu- 
lated in  the  transverse  colon,  deep  successive  tonic  constrictions  appear  and 
force  its  contents  into  the  descending  colon.  When  sufficient  material  has  ac- 
cumulated here,  it  is  evacuated  by  strong  peristalses  combined  with  compres- 
sion by  the  contracting  abdominal  muscles. 

Reverse  or  antiperistalsis  does  not  commonly  occur  in  the  small  intestine, 
but  large  nutrient  enemata  introduced  into  the  rectum  and  colon  may  be  forced 
by  antiperistaltic  waves  in  the  large  intestine  to  and  through  the  ileocecal 
valve  into  the  small  intestine.  Here  they  are  treated  in  the  same  way  as  food 
which  has  been  introduced  in  the  normal  way. 

Influence  of  the  Nervous  System  on  Intestinal  Peristalsis.  As  in 
the  case  of  the  esophagus  and  stomach,  the  peristaltic  movements  of  the  in- 
testines may  be  directly  set  up  in  the  muscular  fibers  by  the  presence  of  food 
acting  as  the  stimulus.  Few  or  no  movements  occur  when  the  intestines  are 
empty.  The  intestines  are  connected  with  the  central  nervous  system  both 
by  the  vagi  and  by  the  splanchnic  nerves,  as  well  as  by  other  branches  of  the 
sympathetic  which  come  to  them  from  the  celiac  and  other  abdominal  plexuses. 
The  relations  of  these  nerves  respectively  to  the  movements  of  the  intestine 
and  the  secretions  are  probably  the  same  as  in  the  case  of  the  stomach  already 
considered. 

The  vagus  fibers  are  described  as  the  motor  fibers  for  the  intestine,  while 
the  sympathetic  are  said  to  be  at  least  in  part  inhibitory.  Various  states  of  the 
central  nervous  system,  such  as  fear,  anger,  etc.,  inhibit  the  intestinal  move- 
ments. The  intestine  carries  out  peristalses  when  isolated  from  the  body  so 
that  the  central  connections  do  not  originate,  but  are  only  regulative.  The 
intestinal   movements  are  essentially  automatic,   depending  on   the  rhyth- 


SALIVA     AND     SALIVARY     DIGESTION  351 

mic  property  of  the  muscle  itself  but  coordinated  by  the  complex  local  nervous 
mechanism. 

The  innervation  of  the  large  intestine  is  also  double  in  character  and 
the  relations  are  doubtless  the  same  as  in  the  small  intestine. 

Defecation.  The  emptying  of  the  rectum  is  essentially  an  involun- 
tary act  which  has  acquired  a  certain  amount  of  voluntary  regulation.  The 
act  is  accomplished  wholly  reflexly  in  dogs  with  isolated  lumbar  cord,  in  fact 
has  been  observed  when  the  lumbar  spinal  c<  rd  was  removed.  In  the  latter 
case  defecation  occurs  by  automatic  peristalsis  of  the  rectum,  while  in  the 
former  cases  reflexes  through  the  lumbar  cord  carry  out  the  act.  The  stimulus 
of  the  feces  against  the  rectum  and  the  internal  sphincter  initiate  the  movement. 

Normally  in  man  the  rectal  stimulus  gives  rise  to  the  consciousness  of 
the  desire  to  defecate  and  the  initiation  of  efferent  nerve  impulses  that  may 
increase  the  contraction  of  the  external  sphincter  and  inhibit  the  act  tempo- 
rarily. During  defecation,  however,  the  voluntary  effort  leads  to  relaxation  of 
the  external  sphincter,  and  the  normal  peristalsis  of  the  rectum  is  supported 
by  contractions  of  the  abdominal  musculature  so  as  greatly  to  increase  the 
abdominal  pressure,  thus  aiding  the  involuntary  reflex. 

LABORATORY  EXPERIMENTS  IN  DIGESTION. 
I.   SALIVA  AND  SALIVARY  DIGESTION. 

i.  Reflex  Salivary  Secretion.  Saliva,  which  is  the  mixed  secretion 
of  the  salivary  and  buccal  glands,  is  produced  more  or  less  intermittently.  Ex- 
amine, taste,  or  smell  appetizing  food,  for  example,  an  apple,  the  salivary  glands 
begin  to  discharge  secretion  which  is  poured  into  the  mouth  more  rapidly 
than  under  ordinary  conditions.  This  increased  activity  is  a  reflex  secretion. 
It  is  brought  about  by  the  stimulation  of  sensory  structures  which  lead  to 
afferent  nerve  impulses  reacting  on  nerve  centers  in  the  medulla  to  cause 
secretory  nerve  impulses  to  the  glands.  The  stimulating  effect  of  food  in  the 
mouth  causes  the  most  rapid  reflex  secretion,  which  may  last  through  several 
minutes,  or  even  hours.  Especially  stimulating  substances  are,  beside  food, 
such  substances  as  tartaric  acid,  lemon  juice,  ether,  alcohol,  etc.,  in  fact  any- 
thing that  produces  strong  local  irritation  will  lead  to  reflex  secretion. 

2.  The  Secretory  Nerves  of  the  Salivary  Glands  of  the  Dog.  The 
nervous  mechanism  for  the  salivary  gland  is  well  known,  and  the  anatomical 
relations  are  such  as  to  make  this  gland  a  favorable  one  for  studying  the  nerv- 
ous mechanism  of  glands  in  general. 

Anesthetize  a  dog  and  bind  it  to  a  suitable  holder.  Expose  the  nerves  to 
the  submaxillary  gland  as  follows:  cut  through  the  skin  of  the  lower  jaw  along 
the  inner  border  for  about  3  inches.  Isolate  and  double  ligate  the  jugular 
vein  and  any  other  veins  in  the  field  except  the  ones  coming  from  the  sub- 


352  FOOD     AND     DIGESTION 

maxillary  gland.  Isolate  and  cut  the  digastric  muscle,  also  the  mylo-hyoid, 
using  pains  not  to  injure  the  duct  of  the  gland  or  its  arteries.  When  the 
muscles  are  laid  back,  the  artery  and  accompanying  sympathetic  nerve 
branches,  the  hypoglossal  and  the  lingual  nerves,  the  submaxillary  duct  and 
the  submaxillary  gland,  will  all  be  exposed.  Isolate  and  introduce  a  very 
fine  glass  cannula  into  the  submaxillary  duct.  A  small  nerve  filament 
branches  from  the  lingual  nerve  and  runs  to  the  hilus  of  the  gland,  the  chorda 
tympani.  Carefully  expose  the  chorda,  place  a  silk  ligature  under  it  for  con- 
venience in  handling.    Also  expose  the  sympathetic  filaments  with  the  artery. 

Stimulate  the  chorda  tympani  with  a  mild  induction  current  for  a  few 
minutes  at  a  time  at  intervals,  and  note  that  the  secretion  which  is  absent 
or  forming  slowly  before  stimulation  now  gathers  quickly  and  leaves  the  end 
of  the  cannula  in  a  series  of  drops.  Collect  the  saliva  in  a  small  beaker.  One 
can  measure  the  rate  of  flow  by  collecting  the  saliva  in  a  small  graduated 
cylinder,  or,  by  changing  the  beaker  every  ten  minutes,  making  a  record  of  the 
quantity  of  secretion  formed.  Stimulate  the  sympathetic  fibers,  cutting  the 
hypoglossal  nerve  if  necessary,  and  note  that  the  secretion  is  very  slightly  in- 
creased, but  the  increase  lasts  for  only  a  few  minutes.  If  the  sympathetic 
fibers  are  stimulated  before  the  chorda,  then  the  sympathetic  secretion  is 
relatively  less  than  if  the  order  of  stimulation  is  reversed. 

During  stimulation  of  the  nerves,  note  the  relative  flow  of  blood  through 
the  organ.  During  chorda  stimulation  the  flow  is  increased;  during  sympa- 
thetic stimulation  it  is  decreased,  as  these  nerves  contain  vaso-dilator  and 
vaso-constrictor  fibers,  respectively. 

3.  Microscopic  Changes  in  the  Gland  Cells.  Make  a  histological 
preparation  (by  any  standard  method  of  fixing  and  staining)  of  the  submaxil- 
lary gland  of  the  cat,  a,  taken  after  a  period  of  several  hours'  fasting  when 
the  gland  cells  may  be  assumed  to  be  at  rest;  and  b,  immediately  after  a  period 
of  activity  (from  eating,  or  activity  secured  by  the  stimulation  of  the  chorda 
tympani)  and  note:  a,  The  cells  from  the  resting  gland  are  relatively  larger, 
the  nuclei  are  pushed  back  against  the  basement  membrane,  they  have 
sparsely  sustaining  protoplasm,  and  the  cells  are  crowded  with  large  gran- 
ules, which  in  a  fortunate  preparation  fill  the  entire  cell.  The  outlines  of  the 
cells  are  relatively  indistinct  and  the  lumen  of  the  gland  is  small,  b,  The  cells 
of  the  active  gland  are  relatively  small,  the  nuclei  are  centrally  placed,  the 
protoplasm  stains  more  definitely,  the  granules  are  usually  present  but  limited 
to  the  side  of  the  cell  next  to  the  lumen,  the  outlines  of  the  cells  are  distinct, 
and  the  lumen  is  often  quite  large. 

4.  The  Chemical  Composition  of  Saliva.  Collect  several  cubic  cen- 
timeters of  saliva  as  follows:  Wash  the  mouth  thoroughly  with  water,  then 
induce  secretion  of  saliva  by  chewing  a  bit  of  paraffin  or  a  piece  of  thoroughly 
washed  rubber.  The  inhalation  of  ether  vapor  will  often  facilitate  the  reflex 
secretion.     One  should  avoid  strong  acids  to  induce  secretion  unless  their 


DIGESTIVE    ACTION     OF    SALIVA     ON    STARCH  353 

presence  is  to  be  taken  into  consideration  afterward.  Make  the  following 
tests : 

Reaction.  A  slip  of  neutral  litmus  paper  when  introduced  into  freshly 
collected  saliva,  or  for  convenience  simply  taken  into  the  mouth  during  sali- 
vary secretion,  shows  an  alkaline  reaction. 

Mucin.  To  3  or  4  c.c.  of  saliva  add  2  per  cent  acetic  acid  drop  by  drop 
until  distinct  acidity  is  obtained.  On  stirring  the  saliva  with  a  glass  rod  a 
sticky  mucin  makes  its  appearance. 

Potassium  Sulphocyanide.  To  2  c.c.  of  saliva  in  a  test  tube  add  2  or  3 
drops  of  ferric-chloride  solution,  slightly  acidulated  with  hydrochloric  acid, 
a  reddish-brown  coloration  indicates  the  presence  of  potassium  sulphocyanide. 
One  should  run  a  blank  test  on  distilled  water  for  comparison. 

Chlorides.  Add  silver  nitrate  to  2  c.c.  of  saliva  after  first  removing  the 
proteids.  A  white,  cloudy  precipitate,  which  disappears  on  adding  ammonia 
and  reappears  on  adding  nitric  acid,  indicates  the  presence  of  chlorides. 

Proteids.  Remove  the  mucin  from  a  sample  of  saliva,  as  above,  and  test 
by  the  characteristic  proteid  reactions.  A  faint  trace  of  proteid  can  usually 
be  demonstrated. 

5.  Digestive  Action  of  Saliva  on  Starch.  Review  the  test  for  starch, 
dextrin,  and  dextrose,  as  preparation  for  an  identification  of  these  prod- 
ucts of  salivary  digestion.  To  50  c.c.  of  1  per  cent  starch  paste  in  the 
water  bath  at  400  C.  add  5  c.c.  of  saliva,  and  mix  thoroughly  with  a  glass  rod. 
Immediately  begin  two  series  of  tests:  a,  for  the  presence  of  starch;  b,  for 
the  presence  of  reducing  sugar.  The  tests  for  starch  can  be  made  by  adding 
to  3  drops  of  starch,  on  a  porcelain  plate,  an  equal  quantity  of  dilute  iodine 
in  potassium  iodide  solution.  Use  a  glass  rod.  Make  the  tests  every  2  minutes 
for  20  minutes.  The  tests  for  reducing  sugar  are  best  made  by  placing  2  c.c. 
of  Fehling's  solution  in  each  of  a  series  of  test  tubes  and  adding,  at  intervals 
of  5  minutes,  1  c.c.  from  a  dropping-pipet  and  boiling.  If  the  tests  are  set 
away  as  fast  as  they  are  prepared,  a  reddish-yellow  cuprous  oxide  will  settle 
out,  and  the  series  will  give  a  rough  comparison  as  to  the  quantity  of  reducing 
sugar  present. 

In  the  first  series  the  deep  blue  of  the  starch  reaction  quickly  changes 
to  a  reddish-blue,  a  red,  a  reddish-brown,  until  finally  no  change  in  cclrr 
other  than  that  produced  by  the  mixture  of  the  iodine  occurs,  showing  that 
the  starch  has  passed  the  second  stage  of  erythro-dextrin  in  its  disappearance. 
The  indication  of  reducing  sugar  in  the  second  series  shows  that  this  erythro- 
dextrin  has  been  transformed  into  reducing  sugar,  and  also  that  the  amount 
of  sugar  is  greatly  increased  during  the  progress  of  the  test. 

6.  The  Influence  of  Temperature  on  Salivary  Digestion.  Prepare 
three  test  tubes,  a,  b,  c,  containing  4  c.c.  each  of  saliva.  Boil  a,  place  b  in 
a  water  bath  at  400  C,  and  place  c  in  ice  water.  After  c  has  been  cooled  down 
to  the  temperature  of  the  ice  bath  add  to  each  2  c.c.  of  1  per  cent  starch  solu- 

23 


354 


FOOD     AND     DIGESTION 


tion  and  mix.  At  intervals  of  2  to  5  minutes  test  these  3  samples  for  the  dis- 
appearance of  starch  and  appearance  of  reducing  sugar,  as  in  experiment  5. 
No  change  will  take  place  in  a;  b  will  be  quickly  digested;  and  the  digestion 
in  c  will  be  slight  or  suspended.  Upon  placing  c  in  a  warm  bath  digestion  will 
quickly  occur. 

7.  Influence  of  Acids  and  Alkalies  on  Salivary  Digestion.  To 
each  of  5  test  tubes,  a,  b,  c,  d,  e,  add  5  c.c.  of  saliva.  Leave  a  for  the  normal; 
make  b  strongly  alkaline;  c  exactly  neutral;  d  acid  to  the  extent  of  0.2  to  0.3  per 
cent  hydrochloric  acid;  e  strongly  acid.  Place  all  in  the  water  bath  at  400  C. 
Add  to  each  2  c.c.  of  1  per  cent  starch  paste  and  mix.  Test  for  starch  and  for 
reducing  sugar  at  intervals  of  20  minutes  and  compare,  noting  the  results 
in  the  following  table: 


A 

B 

C 

D 

K 

Prepare  and  set 
in   water  bath 
at  40    C. 

5  c.c.  saliva 

5  c.c.  saliva 

and 

1  c.c.  strong 

KOH 

5  c.c.  saliva 

exactly 
neutralized 

5  c.c.  saliva 

and 
1  c.c.  0.2  per 
cent  hydro- 
chloric acid 

5  c.c.  saliva 

and 
1  c.c.  strong 
hydrochlo- 
ric acid 

Then  add 

2  c.c.  1  per 
cent  starch 

2  c.c.  1  per 
cent  starch 

2  c.c.  1  per 
cent  starch 

2  c.c.  1  per 
cent  starch 

2  c.c.  1  per 
cent  starch 

Test   for  starch 
and  sugar  im- 
mediately. 

After  20  minutes. 

After  40  minutes. 

The  results  obtained  in  the  experiments  5,  6,  and  7  show  that  starch  is 
converted  into  reducing  sugar,  and  furthermore  that  the  conditions  for  its 
conversion  indicate  that  the  change  is  accomplished  by  an  amylolytic  enzyme 
which  in  this  case  is  called  ptyalin. 

8.  The  Action  of  Ptyalin  is  Favored  by  the  Removal  of  the  End 
Products.  Place  50  c.c.  of  2  per  cent  starch  paste  in  a  dialyzing  tube  or 
paper,  suspend  in  a  beaker  of  running  water.  Take  50  c.c.  of  the  same  solution 
in  a  beaker,  to  each  add  2  c.c.  of  saliva  and  mix  thoroughly.  Test  for  the  dis- 
appearance of  starch  at  intervals  of  20  minutes.  The  starch  in  the  dialyzing 
tube  will  disappear  first  because  the  reducing  sugar  passes  out  through  the 
dialyzer,  while  in  the  beaker  it  is  retained  and  hinders  the  further  action  of 
ptyalin. 


GASTRIC     DIGESTION 


355 


II.  GASTRIC  JUICE  AND  GASTRIC  DIGESTION. 

9.  The  Secretion  of  Gastric  Juice.  The  conditions  which  influence 
gastric  secretion  can  be  readily  observed  on  the  dog  with  a  gastric  fistula. 
Take  a  dog  which  has  had  a  gastric  fistula  prepared  some  weeks  before  and 
which  is  in  a  condition  of  hunger,  place  him  in  a  holder  with  a  cup  suspended 
to  collect  the  gastric  juice,  and  exhibit  before  the  dog  some  fresh  meat  or 
other  food  which  he  enjoys,  but  do  not  allow  him  to  cat  it.  After  teasing  the 
animal  for  5  or  10  minutes,  an  abundant  flow  of  gastric  juice  will  begin.  Paw- 
low  calls  this  the  psychic  secretion. 

If  an  esophageal  fistula  has  also  been  performed  on  the  animal  the  dog 
may  be  allowed  to  eat  the  meat,  of  course  swallowing  it  out  of  the  esophageal 


Fig.  27S. — -Operation  on  the  Stomach  to  Form  an  Isolated  Pouch  with  Nerves  Intact. 
Isolated  sac;    I',  cavity  of  stomach;    .1,  A,  opening  at  the  abdominal  wall. 


fistula  back  into  the  plate.  In  this  experiment  an  abundant  How  of  gastric 
secretion  takes  place  and  may  continue  for  an  hour  or  more. 

If  a  gastric  pouch  has  been  performed  by  Pawlow's  method,  the  animal 
may  be  allowed  to  eat  the  food,  swallowing  it  into  the  stomach.  In  this  case 
the  reflex  secretion  just  described  takes  place  as  usual,  but  is  followed  after 
an  hour  or  an  hour  and  a  half  by  a  second  increase  in  the  quantity  of  secretion. 
This  second  increase  has  been  ascribed  to  the  reflexes  originating  in  the 
stomach,  possibly  from  the  reflex  stimulating  action  of  the  digestive  products 
themselves. 

10.  Composition  of  Gastric  Juice.  Test  a  sample  of  gastric  juice 
obtained  from  a  gastric  fistula,  as  follows: 

Reaction.     Gastric  juice  is  strongly  acid.     Test  for  free  hydrochloric  acid 


356  FOOD    AND     DIGESTION 

as  follows:  Gastric  juice  turns  congo-red  to  a  blue  color.  Organic  acids  pro- 
duce violet.  Gastric  juice  plus  0.5  per  cent  alcoholic  solution  of  dimethyl- 
amido-azobenzol  develops  a  cherry-red  color,  a  reaction  that  is  given  by  free 
hydrochloric  acid.  Combined  hydrochloric  acids  and  organic  acids  do  not  give 
the  color.  Giinzburg's  reagent,  consisting  of  2  per  cent  phloroglucin  and  1 
per  cent  vanillin  in  80  per  cent  alcohol,  produces  a  rose-colored  mirror 
on  porcelain  in  the  presence  of  free  hydrochloric  acid.  The  test  is  very 
delicate. 

Proteids.  The  usual  proteid  tests  can  be  applied  to  gastric  juice  and  show 
that  it  contains  small  quantities. 

11.  Artificial  Gastric  Juice.  An  active  principle,  pepsin,  of  gastric 
juice  can  be  obtained  by  extracting  the  gastric  mucous  membrane  of  the 
dog,  pig,  etc.  Scrape  off  the  mucous  membrane,  grind  it  to  a  fine  pulp  by 
repeatedly  running  it  through  a  sausage  machine,  or  by  pounding  in  a  mortar 
with  clean  sand.  The  mucous  membrane  should  be  allowed  to  stand  for 
three  or  four  hours  before  extraction,  otherwise  the  zymogen,  and  not  the 
enzyme,  will  be  obtained.  Extract  a  portion  of  this  gastric  pulp  in  water,  and 
filter.  Or  extract  with  glycerin  for  several  weeks  and  filter.  Either  of  these 
extracts  contains  the  enzyme.  A  solution  of  the  glycerin  extract  in  0.2  per 
cent  hydrochloric  acid  contains  all  the  properties  of  gastric  juice.  This  is 
known  as  artificial  gastric  juice. 

Commercial  pepsin  already  prepared  can  be  obtained  on  the  market. 
Artificial  gastric  juice  is  made  from  commercial  pepsin  by  adding  3  to  5  grams 
to  a  liter  of  0.2  per  cent  hydrochloric  acid. 

12.  Digestive  Action  of  Gastric  Juice,  or  Artificial  Gastric  Juice. 
The  digestive  action  of  gastric  juice  is  limited  to  proteids.  Shreds  of  fibrin 
which  permit  the  gastric  juice  to  come  in  intimate  contact  with  all  parts  of 
the  material,  form  the  best  proteid  for  testing  the  action  of  this  enzyme. 
Prepare  a  series  of  test  tubes,  a,  b,  c,  d,  each  containing  5  c.c.  of  artificial 
gastric  juice.  Add  to  a  some  shreds  of  fibrin;  to  b  some  boiled  white  of  an  egg; 
to  c  some  fibers  of  boiled  meat;  to d  some  fibers  of  raw  meat;  place  in  a  warm 
bath  at  400  C.  and  examine  at  intervals  of  20  minutes.  Tabulate  the  results 
by  the  plan  indicated  in  experiment  13,  noting  particularly  the  rapidity  with 
which  the  proteid  goes  into  solution. 

13.  Conditions  Affecting  the  Enzyme  Action  of  Gastric  Juice. 
Prepare  a  series  of  test  tubes  containing  5  c.c.  each  of  gastric  juice,  according 
to  the  table  on  the  following  page.  Add  a  definite  quantity  of  fibrin  to  each 
and  note  the  changes  at  intervals  of  20  minutes. 

14.  Cleavage  Products  of  Gastric  Digestion.  Add  5  to  10  grams 
of  fibrin  to  100  c.c.  of  artificial  gastric  juice  in  a  flask  and  place  in  a 
water  bath  at  400  C.  After  one  hour  filter  off  40  c.c.  Exactly  neutralize  this 
filtrate  with  1  per  cent  potassium  hydrate.  A  precipitate  makes  its  appearance, 
and  can  be  collected  on  the  filter  paper,  washed  with  distilled  water,  and  dis- 


ACTION    OF    RENNIN 


357 


solved  in  i  per  cent  dilute  hydrochloric  acid,  acid  albumin.  Test  for  the  pro- 
teid  reactions. 

After  two  hours  filter  the  remaining  60  c.c,  exactly  neutralize  to  remove 
any  traces  of  acid  albumin,  and  filter.  The  filtrate  contains  proteoses.  Con- 
centrate the  filtrate  over  a  water  bath  to  one-fourth  its  volume,  add  an  equal 
quantity  of  saturated  ammonium-sulphate  solution,  a  sticky  precipitate  of 
primary  proteoses  separates  out.  Collect  on  a  filter  paper,  wash  with  half- 
saturated  ammonium  sulphate,  redissolve  in  very  dilute  salt-solution,  and 
test  for  proteid  reactions.  The  primary  proteoses  are  precipitated  by  nitric 
acid. 

To  the  filtrate  from  the  half-saturated  ammonium  sulphate  add  crystals  of 
ammonium  sulphate  until  complete  saturation  with  salt.    Deutero-albumoses 


A 

B 

c 

D 

E 

5  c.c.  gas- 
tric juice  at 
400  'C. 

5  c.c.  neutral 

gastric  juice 

at  400  C. 

5  c.c.  alka- 
line gastric 
juice  at  400  C. 

5  c.c.  boiled 

gastric  juice 

at  400  C. 

5  c.c.  gastric 
juice  at  o°  C. 

Then  add 

Fibrin 

Fibrin 

Fibrin 

Fibrin 

Fibrin 

Note  after  20 
minutes. 

After  40  minutes. 

After  60  minutes. 

separate  out.    Collect  on  a  filter  paper,  wash,  dissolve,  and  test  for  proteids. 
The  secondary  proteoses  are  not  precipitated  by  nitric  acid. 

Finally  the  filtrate  contains  peptone.  It  can  be  isolated  and  tested  by 
concentrating  over  the  water  bath,  adding  barium  hydrate  to  slight  excess 
to  remove  the  sulphate,  filtering,  and  precipitating  the  excess  of  barium  by 
exact  neutralization  with  1  per  cent  sulphuric  acid.  Test  for  proteid  reac- 
tions. Peptone  gives  a  rose  color  in  the  biuret  reaction.  The  xanthoproteic 
reaction  gives  the  color  change,  but  not  the  usual  precipitate.  Peptone  is  re- 
dissolved  from  its  alcoholic  precipitate  without  change.    It  is  dialyzable. 

15.  Action  of  Rennin.  Add  a  solution  of  commercial  rennin  (jun- 
ket powder),  or  of  the  extract  of  gastric  mucous  membrane  of  the  fourth 
stomach  of  a  calf,  to  5  c.c.  of  milk  and  let  stand  for  a  few  minutes.  Repeat 
the  test  with  artificial  gastric  juice.  Also  with  neutral  gastric  juice.  In  each 
case  the  milk  will  form  a  jelly-like  clot,  which  is  firmer  in  the  test  tube  contain- 
ing commercial  rennin,     In  the  test  tube  containing  artificial  gastric  juice, 


358  FOOD     AND     DIGESTION 

the  milk  is  first  coagulated,  then  slowly  dissolved  or  digested.    This  clotting 
is  due  to  the  special  coagulating  enzyme,  rennin. 

III.  PANCREATIC  JUICE  AND  PANCREATIC  DIGESTION. 

1 6.  The  Secretion  of  Pancreatic  Juice.  If  a  dog  containing  a  pan- 
creatic fistula  made  by  Pawlow's  method  is  available,  then  try  the  experi- 
ment of  feeding  the  animal  and  noting  the  rate  of  secretion  of  pancreatic 
juice  through  a  period  of  two  hours.  When  the  gastric  digestion  has  proceeded 
to  the  point  where  the  acid  chyme  may  be  supposed  to  have  entered  the  duo- 
denum, then  a  sharp  increase  in  the  flow  of  pancreatic  juice  takes  place.  This 
increased  activity  will  last  through  a  period  of  two  or  three  hours  or  more. 
It  is  produced  either  by  nerve  reflexes  (Pawlow)  or  by  the  influence  of  the 
secretion  produced  by  the  gastric  mucous  membrane  when  stimulated  by  acid. 

17.  Influence  of  Secretin  on  the  Rate  of  Secretion.  Make  an  ex- 
tract of  the  intestinal  mucous  membrane,  preferably  from  the  duodenum, 
by  scraping  off  the  membrane,  grinding  it  to  a  pulp,  and  extracting  it  over  a 
water  bath  in  0.2  per  cent  hydrocholoric  acid,  and  filtering. 

Anesthetize  a  large  dog,  open  the  abdomen,  isolate  the  pancreatic  duct, 
introduce  a  cannula,  and  arrange  for  the  collection  of  pancreatic  juice.  Intro- 
duce a  cannula  into  the  saphenous  vein  and  connect  it  with  a  buret  containing 
the  extract  of  secretin  already  prepared.  Inject  5-c.c.  quantities  of  the  secretin 
solution  into  the  vein  at  intervals  of  ten  minutes.  Measure  the  rate  of  secretion 
of  pancreatic  juice  by  counting  the  drops  per  minute,  or  if  the  secretion  is 
rapid  enough,  by  collecting  it  at  intervals  of  five  or  ten  minutes  and  measuring 
it  in  a  graduated  pipet. 

This  method  will  often  yield  enough  pancreatic  juice  in  the  course  of  a 
couple  of  hours  to  make  the  pancreatic  experiments  which  follow.  Bayless 
and  Starling  call  it  secretin  juice. 

18.  Chemical  Characters  of  Pancreatic  Juice.  Test  the  reaction, 
proteid,  salt,  etc.,  content  of  the  sample  of  pancreatic  juice  collected  in  the 
last  experiment. 

19.  Artifical  Pancreatic  Juice.  Artificial  pancreatic  juice  can  be 
prepared  from  the  pancreas  by  grinding  and  macerating  and  extracting  a 
pancreas  with  water  or  glycerin,  as  described  for  the  gastric  glands  in  experi- 
ment 11  above.  Commercial  preparations  of  pancreatic  enzyme  can  be  ob- 
tained on  the  market.  A  solution  of  glycerin  extract  of  pancreatic  gland  or 
of  commerical  pancreatin  in  0.2  per  cent  sodium  carbonate  is  known  as  arti- 
ficial pancreatic  juice. 

20.  The  Enzymes  of  Pancreatic  Juice.  The  pancreatic  juice  con- 
tains enzymes  which  have  exerted  a  digestive  action  on  starches,  fats,  and 
proteids.  This  fact  can  be  tested  as  follows:  a,  To  5  c.c.  of  artificial  pancreatic 
juice  add  2  c.c.  of  1  per  cent  starch  paste,  mix  and  set  in  the  water  bath  at  400  C. 


ACTION    OF    THE     ENZYMES     OF     PANCREATIC     JUICE 


359 


b,  To  i  c.c.  of  pancreatic  juice  (artificial  juice  is  not  active),  collected  in  experi- 
ment 17,  add  0.5  c.c.  of  neutral  olive  oil,  and  place  over  a  water  bath,  c,  To  5  c.c. 
of  artificial  pancreatic  juice  add  a  few  flocks  of  fibrin.  Test  the  digestive 
action  on  starch  by  the  iodine  test  for  the  disappearance  of  starch,  or  by  the 
copper-reduction  test  for  the  presence  of  reducing  sugar.  Test  the  fat  by  its 
reaction,  noting  that  the  neutral  or  slightly  alkaline  solution  has  become  acid, 
also  by  the  fact  that  an  emulsion  has  been  formed.  Note  that  the  proteid 
has  gone  into  solution. 

The  digestive  action  on  starch  is  due  to  the  enzyme  amylopsin,  or  pan- 
creatic diastase,  as  it  is  sometimes  called.  The  fat-splitting  effect  is  due  to  the 
enzyme  lipase,  and  the  solution  of  the  fibrin  is  accomplished  by  the  proteolytic 
enzyme,  trypsin. 

21.  Conditions  which  Influence  the  Action  of  the  Enzymes  of 
Pancreatic  Juice.  To  each  of  5  test  tubes,  a,  b,  c,  d,  e,  add  5  c.c.  of 
artificial  pancreatic  juice.  Place  a,  b,  c,  d  in  the  water  bath  at  400  C,  and  e 
into  an  ice  bath.  Leave  a  normal,  make  b  exactly  neutral,  add  to  c  1  c.c.  of  2 
per  cent  hydrochloric  acid,  and  boil  d .  Add  to  each  tube  2  c.c.  of  1  per  cent 
starch  paste.  Follow  the  digestive  changes  by  the  tests  previously  outlined. 
Tabulate  according  to  the  following  scheme: 


A 

B 

c 

D 

E 

Take 

5  c.c.  pan- 
creatic 
juice  400  C. 

Neutralize 
5  q.c.  pan- 
creatic juice 
400  C. 

5  c.c.  pancre- 
atic juice  and 
1  c.c.  of  2  per 
cent  hydro- 
chloric acid 
400  C. 

5  c.c.  pan- 
creatic 
juice  and 
boil. 

5  c.c.  pan- 
creatir 
juice  at  o°  C. 

Then  add 

2  c.c.  of 
starch 

2  c.c.  of 
starch 

2  c.c.  of 
starch 

2  c.c.  of 
starch 

2  c.c.  of 
starch 

Note    after    20 
minutes. 

After    40    min- 
utes. 

After    60    min- 
utes. 

Repeat  this  experiment  with  a  second  set  of  test  tubes  containing  fibrin. 
Lipase  is  not  very  active  in  artificial  pancreatic  juice  and  may  be  omitted. 
If  pancreatic  juice  is  available  make  a  third  set  containing  fat. 

22.  Cleavage  Products  of  Pancreatic  Digestion.     To  200  c.c  of  arti- 


360  FOOD     AND     DIGESTION 

ficial  pancreatic  juice  add  25  grams  of  moist  fibrin  and  place  in  a  water  bath 
at  400  C,  add  7  c.c.  of  chloroform  to  prevent  putrefactive  changes.  After  three 
or  four  hours  filter  off  80  c.c.  and  place  the  remainder  on  the  water  bath  for 
two  or  three  days.  Test  the  filtrate  for  alkali  albumin,  albumoses,  and  pep- 
tones, by  the  method  outlined  in  experiment  14  above. 

Filter  the  second  portion  and  concentrate  to  a  syrupy  mass  on  the  water 
bath.  Crystals  make  their  appearance.  Pour  off  the  fluid,  wash  the  crystals 
with  cold  water,  and  examine  under  the  microscope  for  sheaves  of  tyrosin. 
The  filtrate  contains  lencin. 

If  the  digestion  had  been  allowed  to  proceed  without  the  chloroform, 
bacteria  would  have  appeared  in  the  solution,  and  proteid  cleavage  products, 
due  to  their  action,  would  be  found,  notably  indol. 

IV.  BILE  AND  INTESTINAL  JUICE. 

23.  Bile.  Secure  bile  from  the  gall-bladder  of  a  pig  or  dog,  or,  if 
it  is  possible,  a  sample  of  human  bile.  Test  the  reaction  which,  in  fresh 
bile,  is  neutral.  Test  for  mucin;  albumin;  and  for  iron;  hydrochloric  acid 
and  ferrocyanide  of  potassium  give  a  blue  color  when  iron  is  present. 

Bile  Salts.  Evaporate  10  c.c.  of  bile  to  complete  dryness,  mix  with  animal 
charcoal,  add  50  c.c.  of  absolute  alcohol,  filter;  add  an  excess  of  ether  to  the 
filtrate,  which  gives  a  white  precipitate  of  bile  salts.  Crystals  will  form  on 
standing  in  a  well-stoppered  flask  for  a  day  or  two. 

Bile  Acids.  A  drop  of  syrup  of  cane-sugar  in  a  test  tube  of  bile  forms  a 
deep  red-purple  color  at  the  line  of  separation  from  concentrated  sulphuric 
acid.    Furfur  aldehyde  with  cholalic  acid  gives  the  color. 

Bile  Pigments.  With  1  c.c.  of  bile  in  a  test  tube  strong  nitroso-nitric 
acid  produces  a  play  of  colors  beginning  with  green,  blue,  red,  and  yellow — 
Gmelin's  test. 

Bile  does  not  contain  digestive  enzymes,  but  the  bile  wets  the  mucous 
surface  of  the  intestine  and  facilitates  the  solution  of  fats  and  fatty  acids. 

24.  Intestinal  Juice.  The  secretion  of  the  mucous  membrane 
of  the  small  intestine  has  been  proven  to  have  a  weak  digestive  action  on  pro- 
teids  and  perhaps  on  starches.  It  can  be  obtained  from  an  intestinal  fistula. 
Its  chief  digestive  importance  consists  in  the  presence  of  the  activating  enzyme, 
enterokinase.  Enterokinase  can  be  prepared  by  extracting  the  mucous  mem- 
brane of  the  small  intestine  by  the  method  outlined  for  making  a  pancreatic 
extract. 

To  two  test  tubes  containing  5  c.c.  of  artificial  pancreatic  juice,  or  pref- 
erably containing  secretin  pancreatic  juice,  add  flocks  of  fibrin.  Keep  one 
for  the  control,  to  the  other  add  2  c.c.  of  enterokinase  solution.  The  test  tube 
containing  enterokinase  will  digest  more  rapidly  and  more  effectively  than 
the  other. 


CHAPTER  IX 

ABSORPTION 

Absorption  in  its  restricted  use  means  the  process  by  which  the  digested 
foods  pass  through  the  walls  of  the  alimentary  canal  and  into  the  circulation. 
In  its  more  general  meaning  absorption  is  the  process  by  which  substances 
pass  from  one  part  of  the  body  to  another  by  means  other  than  the  blood- 
and  lymph-vessels.  Usually  the  absorption  takes  place  from  a  free  surface, 
such  as  the  alimentary  canal,  the  skin,  and  the  lungs. 

The  alimentary  canal  is  lined  throughout  with  a  continuous  layer  of  epi- 
thelial tissue.  This  layer  is  only  a  single  cell  thick  in  most  of  its  extent, 
but  nevertheless  it  effectively  separates  the  food  inside  the  canal  from  the 
lymph  in  the  tissue  interspaces  on  the  outside  of  the  mucous  membrane. 
These  spaces  are  separated  from  the  blood  in  the  adjacent  blood-vessels  by  a 
second  continuous  layer,  the  endothelial  walls  of  the  capillaries.  The  food, 
therefore,  in  its  absorption,  must  pass  through  two  layers  of  tissue  to  reach 
the  blood  stream.  But  the  submucous  lymphatic  spaces  and  vessels  furnish 
channels  which  may  carry  substances  into  the  blood  by  way  of  the  thoracic 
duct.  The  mucous  membrane  is,  therefore,  the  one  strict  barrier  through 
which  the  food  must  pass  in  the  act  of  absorption. 

The  exact  methods  by  which  absorption  takes  place  have  long  been  a 
subject  of  controversy  and  of  research.  But  this  problem  is  of  such  diffi- 
culty that  it  is  yet,  in  the  main,  unsolved.  Known  physical  and  chemical 
laws  were  thought  to  explain  the  facts  of  absorption.  Some  of  the  known 
physical  factors  concerned  in  absorption  and  elimination  have  already  been 
considered  in  a  former  chapter,  osmosis  and  diffusion,  Chapter  IV.  A  third 
factor,  filtration,  consists  in  the  passage  of  a  fluid  under  pressure  through  a 
membrane.  These  factors  undoubtedly  play  an  important  role  in  the  passage 
of  solutions  through  the  alimentary  mucous  membrane  and  the  walls  of  the 
blood-vessels.  The  part  which  the  physical  factors  play  is  probably  more 
pronounced  in  the  absorption  of  water  and  crystalloids.  The  nature  of  the 
fluid  within  the  digestive  tract,  and  the  movements  of  the  walls  of  the  stomach 
and  intestines  by  means  of  which  the  material  to  be  absorbed  is  brought 
into  intimate  contact  with  the  absorbing  membrane,  are  additional  factors 
which  influence  absorption. 

But  the  mechanical  and  physical  factors  do  not  fully  explain  the  observed 
facts  of  absorption.     It  becomes  more  and  more  evident  that  there  is  an 

361 


362  ABSORPTION 

unexplained  factor  bound  up  in  the  characteristics  of  the  living  protoplasm 
of  the  epithelial  cells  themselves.  When  isotonic  blood  serum  is  introduced 
into  the  intestine  the  salts  and  water  are  at  once  absorbed,  also  the  albumins, 
but  more  slowly.  In  this  experiment  the  osmotic  conditions  are  in  balance 
and  the  pressure  is  greater  on  the  side  of  the  blood-vessels,  so  that  absorption 
takes  place  with  the  actual  expenditure  of  energy.  The  important  fact 
here  is  that  the  absorption  through  a  living  membrane  is  influenced  by  the 
membrane  in  ways  that  we  cannot  yet  explain.  It  is  this  factor  which  de- 
termines the  different  rate  of  absorption  and  the  so-called  selective  absorp- 
tion in  different  regions  of  the  alimentary  canal. 

As  a  rule,  the  current  of  absorption  is  from  the  stomach  or  intestine  into 
the  blood;  but  the  reversed  action  may  occur,  as,  for  example,  when  sulphate 
of  magnesium  is  taken  into  the  alimentary  canal.  In  this  case  there  is  a 
rapid  discharge  of  water  from  the  blood-vessels  into  the  canal.  The  rapidity 
with  which  matters  may  be  absorbed  and  diffused  through  the  textures  of 
the  body  has  been  found  by  experiment.  It  appears  that  lithium  chloride 
may  be  diffused  into  all  the  vascular  textures  of  the  body,  and  into  some 
of  the  non-vascular,  as  the  cartilage  of  the  hip  joint,  as  well  as  into  the  aque- 
ous humor  of  the  eye,  in  a  quarter  of  an  hour  after  being  given  by  way  of  the 
mouth  and  on  an  empty  stomach.  Lithium  carbonate,  when  taken  in  five- 
or  ten-grain  doses  on  an  empty  stomach,  may  be  detected  in  the  urine  in 
five  or  ten  minutes;  or,  if  the  stomach  be  full  at  the  time  of  taking  the  dose, 
in  twenty  minutes. 

Absorption  in  the  Mouth.  The  epithelial  lining  of  the  mouth  is 
of  the  thicker  stratified  type  and  the  conditions  are  otherwise  unfavorable 
for  absorption.  Little,  if  any,  absorption  normally  takes  place  in  the  mouth, 
and  the  same  is  true  for  the  esophagus. 

Absorption  in  the  Stomach.  The  mucous  and  submucous  coats  of 
the  stomach,  see  figure  258,  are  well  supplied  with  blood-vessels  and  lym- 
phatics. The  mucous  membrane  is,  however,  so  crowded  with  the  peptic 
glands  that  the  relative  amount  of  absorbing  surface  is  small.  It  is  limited 
to  the  mucous  membrane  around  the  mouths  of  the  glands. 

Recent  experiments  have  shown  that  though  absorption  does  take  place 
in  the  stomach,  it  is  not  as  active  as  was  formerly  supposed,  even  in  the  case 
of  water.  Von  Mering  has  found  that  water  begins  to  pass  from  the  stomach 
into  the  intestine  almost  as  soon  as  it  is  swallowed,  and  that  very  little  of  it 
is  absorbed  from  the  stomach.  Of  500  c.c.  given  by  the  mouth  to  a  large 
dog  with  a  duodenal  fistula,  only  5  c.c.  were  absorbed  in  25  minutes,  the 
rest  having  passed  into  the  intestine.  Peptones,  sugars,  and  salts  are  ab- 
sorbed in  the  stomach,  but  only  to  a  limited  extent.  Peptones  are  not  ab- 
sorbed in  appreciable  amount  unless  present  to  as  much  as  5  per  cent  or 
more.  Examination  of  the  mucous  membrane  during  the  stage  of  active 
digestion  has  revealed  the  presence  of  albumoses.     Sugars,  like  peptones,  are 


ABSORPTION    IN    THE     INTESTINES 


36.'} 


absorbed  by  the  stomach  only  to  a  slight  extent  in  the  weaker  solutions, 
but  are  readily  absorbed  when  the  more  concented  solutions  are  introduced 
into  the  stomach,  five  per  cent  and  over  (von  Mehring).  Fats  are  not  absorbed 
at  all  in  the  stomach.  Even  salts  in  the  stomach  are  not  readily  absorbed 
until  this  concentration  is  from  three  to  four  times  that  of  the  blood.  This 
fact  is  in  direct  opposition  to  the  popular  views  on  the  subject. 

While  some  absorption  does  take  place  in  the  stomach  it  is  evidently  not 
of  any  great  importance  under  normal  conditions.  The  presence  of  alcohol 
has  been  shown  to  increase  the  amount  of  absorption,  and  pepper,  mustard, 
and  such  drugs  as  produce  mild  local  irritation  accomplish  the  same  result. 

Absorption  in  the  Intestines.  The  products  of  digestion  are  all 
absorbed  in  the  small  intestine,  as  is  abundantly  shown  by  experiments. 


W^^j^M^^^^^M^M0§i0f  *• 


Fig.  279. — Scheme  of  Blood-vessels  and  Lymphatics  of  Human  Small  Intestine,  a,  Central 
lacteal  of  villus;  b,  lacteal;  c.  stroma;  d,  muscularis  mucosae;  e,  submucosal  f,  plexus  of  lymph- 
vessels;  g,  circular  muscle  layer;  h,  plexus  of  lymph-vessels;  *',  longitudinal  muscle  layer;  ;",  serous 
coat;  k,  vein;  /.artery;  m,  base  of  villus;  n.  crypt;  <o,  artery  of  villus;  p,  vein  of  villus;  q,  epithe- 
lium.    (Mall.) 


Absorption  from  the  small  intestine  has  been  studied  in  the  human  subject 
in  the  case  of  a  patient  who  had  a  fistulous  opening  in  the  lower  part  of  the 
ileum.  For  example,  85  per  cent  of  the  proteid  of  a  test  meal  was  absorbed 
before  the  food  reached  the  fistul  1.     The  food  passes  slowly  down  the  length 


364 


ABSORPTION 


of  the  small  intestine,  and  the  digestive  changes  produce  a  series  of  cleavages 
which  have  known  osmotic  and  diffusion  properties.  The  question  has  been 
to  determine  which  of  the  cleavage  products  are  most  favorable  for  absorp- 
tion and  the  details  of  the  mechanism. 

The  mucous  membrane  of  the  small  intestine  possesses  special  structures 
for  absorption,  the  villi.  Each  villus  projects  as  a  finger-like  process  into 
the  lumen  of  the  intestine.  Its  single-layered  covering  of  epithelial  cells 
supported  by  a  connective-tissue  framework  brings  a  relatively  large  extent 


Lymphatic    of     head     and 
neck,  right 

Right  internal  jugular  vein 
Right  subclavian  vein 

Lymphatics  of  right  arm 


Receptaculum  chyli 


Lymphatics  of  lower  extrem- 
ities 


Lymphatics  of  head  and 
neck,  left 

Toracic  duct 

Left  subclavian  vein 


Thoracic  duct 


Lacteals 


Lymphatics    of  lower  ex- 
tremities 


Fig.  280. — Diagram  of  the  Principal  Groups  of  Lymphatic  Vessels.     (From  Quain.) 


of  surface  into  contact  with  the  digesting  food,  which  is  thus  separated  from 
a  loop  of  capillaries  and  lymphatic  radicals. 

The  capillaries  of  the  villus  are  connected  with  the  veins  which  contribute 
to  the  portal  vein,  hence  carry  blood  to  the  liver.  The  lacteals  of  the  villus 
contribute  to  the  mesenteric  lacteal  system,  hence  the  chyle  and  lymph  pass 
through  the  mesenteric  glands  and  the  portal  duct  to  the  subclavian  vein 
in  the  neck.  There  are  thus  two  routes  by  which  absorbed  foods  may  reach 
the  general  circulation.     These  paths  can  be  independently  isolated;  and  a 


ABSORPTION    OF     PROTEIDS     FROM    THE     INTESTINES 


365 


study  of  the  composition  of  their  discharge  during  active  absorption  con- 
tributes to  our  knowledge  of  the  course  taken  by  the  different  absorption 
products. 

Absorption  of  Proteids  from  the  Intestines.  Proteid  is  absorbed 
chiefly  in  the  small  intestine,  though  just  exactly  how  cannot  at  present  be 
affirmed.     In  the  preceding  chapter  the  cleavage  products  of  proteid  diges- 


I 


\IW 


Fig.  281. 


Fig.  282. 


Fig.  281. — Superficial  Lymphatics  of  the  Forearm  and  Palm  of  the  Hand,  J. — 5;  Two  small 
glands  at  the  bend  of  the  arm;  6,  radial  lymphatic  vessels;  7,  ulnar  lymphatic  vessels;  8,  8. 
palmar  arch  of  lymphatics;  9,  9',  outer  and  inner  sets  of  vessels;  b,  cephalic  vein,  d,  radial 
vein;  e,  median  vein;  /,  ulnar  vein.  The  lymphatics  are  represented  as  lying  on  the  deep  fascia. 
(Mascagni.) 

Fig.  282. — Lymphatic  Vessels  of  the  Head  and  Neck  and  the  Upper  Part  of  the  Trunk.  (Mas- 
cagni.) J. — The  chest  and  pericardium  have  been  opened  on  the  left  side,  and  the  left  mamma  de- 
tached and  thrown  outward  over  the  left  arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The 
principal  lymphatic  vessels  and  glands  are  shown  on  the  side  of  the  head  and  face,  and  in  the  neck, 
axilla,  and  mediastinum.  Between  the  left  internal  jugular  vein  and  the  common  carotid  artery. 
the  upper  ascending  part  of  the  thoracic  duct  marked  I,  and  above  this,  and  descending  to  2,  the 
arch  and  last  part  of  the  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm  in  the 
mediastinal  glands,  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics,  is  also  shown. 


3GG 


ABSORPTION 


tion  have  been  discussed.  It  was  shown  there  that  albumoses,  peptones, 
peptids,  and  the  amido-acids  are  derived  from  the  proteids  as  digestion 
products.  It  has,  in  the  past,  been  assumed  that  peptone  represents  the 
form  most  freely  absorbed.  No  peptone  has,  however,  been  isolated  from 
the  blood  or  lymph  on  the  vascular  side  of  the  epithelial  membrane.  But 
the  same  may  be  said  with  equal  truth  of  the  other  cleavage  products.  The 
present  supposition  is  that  the  proteids  are  taken  up  by  the  epithelium  and 
synthesized  into  other  and  more  complex  forms  before  being  discharged 
into  the  blood;   or  that  the  digestion  cleavages  arc  further  broken  down  in 


Fig.  283. — A  Small  Portion  of  Medullary  Substance  from  a  Mesenteric  Gland  of  the  Ox.  d,  d, 
Trabecular;  a,  part  of  a  cord  of  glandular  substances  from  which  all  but  a  few  of  the  lymph-cor- 
puscles have  been  washed  out  to  show  its  supporting  meshwork  of  retiform  tissue  and  its  capillary 
blood-vessels  (which  have  been  injected  and  are  dark  in  the  figure);  b,  b,  lymph-sinus,  of  which 
the  retiform  tissue  is  represented  only  at  c,  c.    X  300.      (Kolliker.) 

the  liver  into  elimination  forms,  such  as  urea,  ammonium  carbonate,  etc. 
If  the  intestinal  epithelium  produces  change  in  the  proteid  on  its  passage 
through,  then  it  is  evident  that  absorption  of  proteids  is  more  than  mere 
osmosis  and  filtration.  This  idea  is  further  strengthened  by  the  known 
power  of  the  intestines  to  absorb  certain  albumins,  egg  albumin  for  example, 
which  is  non-diffusible  and  non-dialyzable. 

In  animal  foods,  such  as  eggs,  meat,  etc.,  it  is  estimated  that  about  98  per 
cent  of  the  proteid  is  absorbed;  whereas  in  vegetable  foods,  where  the  pro- 
teid is  often  protected  from  the  action  of  the  digestive  enzymes,  there  may 
be  10  to  15  per  cent  loss.  Analysis  of  the  total  lymph  discharge  of  the  thoracic 
duct  fails  to  show  any  increase  of  proteids  during  active  digestion,  from  which 
it  is  inferred  that  proteids  pass  by  way  of  the  liver. 


ABSORPTION     OF     CARBOHYDRATES     BY     THE     INTESTINES 


367 


From  12  to  15  per  cent  of  the  proteid  remains  in  the  food  as  it  passes  the 
ileocecal  valve.  This  amount,  less  the  loss  in  the  feces,  is  absorbed  in  the 
large  intestine. 

Absorption  of  Carbohydrates  by  the  Intestines.  Carbohydrates 
are  broken  down  to  dextrose,  levulose,  etc.,  and  are  absorbed  as  such.  Even 
the  soluble  cane-sugar  is  split  by  the  invertase  of  the  intestine  into  the  mono- 
saccharides, dextrose  and  levulose.  Starch  is  the  source  of  most  of  the  500 
grams  of  dextrose  absorbed  in  an  average  diet  per  day.  During  the  absorp- 
tion of  a  carbohydrate  meal  the  percentage  of  dextrose  in  the  blood  of  the 
portal  vein  is  increased  over  the  normal  which  is  0.1  to  1.5  per  cent.  This 
excess  of  dextrose  passes  through  the  liver  and  is  temporarily  stored  in  the 


Fig.  284. — Section  of  the  Villus  of  a  Rat  Killed  during  Fat  Absorption,  ep.  Epithelium ;  :tr,  stri- 
ated Vxjrder;  c,  lymph-cells;  c',  lymph-cells  in  the  epithelium;  /,  central  lacteal  containing  disinte- 
grating lymph-corpuscles.      (E.  A.  Schafer.) 

liver  cells  as  glycogen.  In  the  case  of  a  fistula  in  the  receptaculum  chyli, 
the  chyle  contained  less  than  a  half  per  cent  of  the  total  dextrose  absorbed. 

Experiments  on  the  rate  of  absorption  of  the  different  sugars  seem  to 
indicate  that  their  absorption  does  not  follow  known  physical  laws  and  that 
we  must  assume  an  unknown  chemical  factor  in  the  living  protoplasm. 

Dextroses  are  absorbed  readily  by  the  large  intestine. 

Fermentation  process  from  bacterial  growth  produces  certain  acids  from 
the  carbohydrates,  chiefly  in  the  large  intestine.     These  are  readily  absorbed. 

Absorption  of  Fats  by  the  Intestines.  Fats  reach  the  absorbing 
epithelium  in  two  forms,  as  soluble  glycerin  and  soaps  and  as  finely  emulsi- 
fied fats.     The  first  two  are  taken  up  by  the  epithelium   readily   enough, 


368 


ABSORPTION 


but  in  the  last  the  process  of  absorption  is  not  so  clear.  It  is  comparatively 
easy  to  demonstrate  the  presence  of  microscopic  globules  of  fat,  both  in  the 
intercellular  substance  and  in  the  epithelial  cells  themselves.  But  it  has 
been  constantly  noticed  that  there  is  a  clear  zone  along  the  free  borders  of 
the  cells.  Fat  drops  exist  in  the  adjacent  digesting  mass,  and  in  the  deeper 
parts  of  the  cells,  but  not  in  this  border  zone.  Since  the  demonstration  of 
the  reversible  action  of  lipase,  the  view  has  been  strengthened  that  in  the 
very  act  of  absorption  the  emulsified  fats  are  decomposed  and  passed  through 
the  cell  border  only  to  be  resynthesized  in  the  cell  protoplasm.  This  is  of 
course  against  the  strictly  mechanical  view.  The  decreasing  efficiency  of 
fats  when  the  bile,  which  wets  the  mucous  surface  and  dissolves  the  fatty 
acids,  is  withheld  from  the  intestine  also  supports  this  view.  As  absorption 
progresses  the  size  of  the  fat  drops  in  the  epithelial  cells  increases,  a  fact 


Fig.  285. 


-Mucous  Membrane  of  Frog's  Intestine  during   Fat  Absorption,    ep.  Epithelium; 
str,  striated  border;  C,  lymph-corpuscles;  /,  lacteal.     (E.  A.  Schafer.) 


that  is  readily  explained  by  supposing  a  continued  synthesis  and  accumula- 
tion of  fat. 

The  fat  drops  are  ultimately  discharged  into  the  connective-tissue  spaces 
and  finally  pass  into  the  lymph  channels,  the  thoracic  duct,  and  into  the 
blood  of  the  subclavian  vein.  This  is  the  course  taken  by  the  larger  per- 
centage of  the  fat.  However,  some  of  the  fat  is  absorbed  into  the  capillaries 
of  the  villi  and  passes  through  the  liver.  The  presence  of  fat  drops  in  the 
liver  cells  at  certain  times  can  be  ascribed  to  storage  of  this  absorbed  fat. 

It  is  said  that  the  more  readily  emulsified  fats,  those  that  melt  readily  at 
the  body  temperature,  are  the  more  completely  absorbed.  The  efficiency 
of  absorption  is  as  high  as  96  to  98  per  cent  for  the  oils,  and  decreases  sharply 
for  such  fats  as  the  tallows. 

The  large  intestine  is  capable  of  absorbing  fats,  though  not  so  readily 
as  the  small  intestine. 

Absorption  of  Minerals  and  Water  in  the  Intestines.  The  salts 
common  in  the  foods  are  most  of  them  readily  soluble,  dissociate  quite  com- 
pletely in  the  dilute  solutions,  and  diffuse  and  dialyze  readily.  Of  the  salts 
of  the  foods,  the  sodium  and  potassium  cations  and  chlorine  anion  are  the 
most  readily  dissociated  and  are  most  diffusible,  while  the   calcium   and 


ABSORPTION    FROM    THE    SKIN,    THE    LUNGS,    ETC.  369 

magnesium  cations  and  the  sulphate  anion  are  least  diffusible.  These  sub- 
stances pass  through  the  intestinal  epithelial  cells  and  the  intercellular  sub- 
stance; at  least  salts  easily  recognized  by  microchemical  means  have  been 
found  in  both  localities  during  absorption.  It  seems  probable  that  the 
forces  concerned  are  largely  osmosis  and  diffusion. 

Yet  observers  have  not  been  able  to  show  that  the  rate  and  character  of 
the  absorption  of  even  the  salines  obey  the  known  physical  laws.  In  fact 
there  is  evidence  that  some  of  the  salts,  iron  for  example,  are  taken  up  as 
organic  compounds  (hematogens  of  Bunge).  The  activity  of  the  epithelial 
cells  is  to  be  taken  into  account,  even  in  the  absorption  of  salts. 

Water,  which  we  have  seen  is  not  absorbed  in  the  stomach,  is  readily 
absorbed  in  the  small  intestine.  Perhaps  the  bulk  of  the  water  taken  into 
the  system  is  absorbed  in  the  upper  part  of  the  small  intestine.  In  the  large 
intestine,  too,  it  is  absorbed  with  facility  and  in  considerable  quantities. 
The  content  of  the  bowel  is  still  quite  fluid  when  it  enters  the  ascending  colon, 
but  the  feces  are  quite  firm  on  discharge  from  the  rectum.  There  are  many 
analogies  by  which  we  may  suppose  a  controlling  influence  of  the  epithelium 
over  the  process  of  water-absorption.  Among  the  fishes  there  are  species, 
the  salmon  for  example,  in  which  the  blood  maintains  a  relatively  constant 
osmotic  pressure,  and  therefore  salt  content.  In  the  salmon  this  is  about 
the  same  as  that  of  human  blood.  The  blood  is  separated  in  the  gills  by 
an  extremely  thin  epithelium  from  the  water  in  which  the  animals  live,  yet 
these  fishes  go  with  impunity  from  sea  water,  with  two  and  a  half  times  more 
salt  than  the  blood,  to  fresh  water  with  practically  no  salt  at  all.  The  epi- 
thelium of  the  gills  permits  the  passage  of  oxygen,  but  it  does  not  permit 
the  diffusion  or  dialysis  of  the  salts  or  the  water  in  either  direction.  It  is 
possible  that  there  is  a  certain  amount  of  resistance  to  the  passage  of  water 
through  the  walls  of  the  stomach,  while  the  intestinal  epithelium  permits 
water  to  pass  readily. 

The  factors  active  in  absorption  are  under  searching  investigation  at  the 
present  time,  so  that  it  is  reasonable  to  hope  that  the  near  future  will  give 
a  more  exact  understanding  of  this  intricate  subject. 

ABSORPTION  FROM  THE  SKIN,  THE  LUNGS,  ETC. 

The  dry  corneous  stratified  epithelium  covering  the  human  body  pos- 
sesses great  resistance  to  the  absorption  of  most  substances.  The  sebaceous 
secretion  keeps  the  surface  slightly  oily.  Watery  solutions  do  not  readily 
wet  the  surface  and  therefore  do  not  penetrate.  There  is  some  absorption 
of  water  on  prolonged  contact  with  the  skin,  but  the  amount  is  insignificant. 
Medicated  baths,  especially  hot  baths,  may  be  accompanied  by  some  slight 
absorption  of  the  substances  dissolved  in  the  waters;  though  it  must  be 
confessed  that  the  good  effects  of  such  treatment  come  from  other  sources. 
24 


370  ABSORPTION 

On  the  other  hand,  oily  substances  come  in  more  intimate  contact  with 
the  skin  and  penetrate  deeper  and  more  readily.  Therefore  lotions  con- 
taining medicines  are  occasionally  applied  to  the  skin,  and  slow  but  gradual 
absorption  occurs.     The  volatile  oils  penetrate  the  skin  readily. 

The  epithelial  lining  of  the  lungs  seems  peculiarly  adapted  to  the  quick 
absorption  of  all  gases  and  volatile  substances.  This  is  illustrated  by  the 
rapidity  with  which  anesthesia  may  be  accomplished  by  breathing  the  vapors 
of  ether  or  chloroform. 

Solutions  injected  into  or  otherwise  brought  into  contact  with  the  sub- 
dermal  connective  tissue,  the  body  of  a  muscle,  or  the  peritoneal  or  thoracic 
cavity,  very  quickly  pass  into  the  general  circulation.  They  are  practically 
injected  into  the  lymphatic  intercellular  spaces  in  these  instances  and,  of 
course,  are  very  readily  carried  through  the  lymphatic  vessels,  figures  280  and 
282,  to  the  thoracic  duct  and  into  the  blood.  Comparing  the  rapidity  of  ab- 
sorption in  the  cases  mentioned,  that  from  the  muscle  is  most  rapid,  a  fact 
of  medical  importance  in  the  use  of  the  hypodermic  needle  for  the  giving 
of  medicines  in  emergency. 


CHAPTER  X 

EXCRETION 

Every  substance  taken  into  the  body,  in  whatever  form,  must,  in  the 
end,  be  cast  off  again,  no  matter  how  great  the  change  that  may  be  wrought 
during  its  sojourn.  We  have  already  found  that  in  the  lungs  the  expired 
air,  and  in  the  intestine  the  feces,  carry  from  the  body  waste  matters  of  no 
further  use.  We  have  now  to  find  that  the  urine  separated  by  the  kidney 
and  the  sweat  and  sebum  of  the  skin  are  likewise  channels  by  which  the 
body  throws  off  water,  salts,  and  broken-down  organic  matters  of  no  further 
use  to  the  organism.  Of  these  two  organs,  the  skin  and  the  kidney,  the 
latter  is  by  far  the  more  important  in  so  far  as  the  quantity  and  complexity 
of  its  secretion  is  concerned. 

STRUCTURE  AND  FUNCTION  OF  THE  KIDNEYS. 

General  Structure.  The  kidneys  are  two  in  number,  and  are 
situated  deeply  in  the  lumbar  region  of  the  abdomen  on  either  side  of  the 
spinal  column  behind  the  peritoneum.  They  correspond  in  position  to  the 
last  two  dorsal  and  two  upper  lumbar  vertebrae,  the  right  slightly  below 
the  left  in  consequence  of  the  position  of  the  liver  on  the  right  side  of  the 
abdomen.  They  are  about  4  inches  long,  2^  inches  broad,  and  i|  inches 
thick.     The  weight  of  each  kidney  is  about  4^  ounces,  140  grams. 

On  dividing  the  kidney  into  two  equal  parts  by  a  section  carried  through 
its  long  convex  border,  figure  286,  the  main  part  of  its  substance  is  seen  to 
be  composed  of  two  chief  portions  called  respectively  cortical  and  medullary, 
the  latter  being  also  sometimes  called  pyramidal,  from  the  fact  of  its  being 
composed  of  about  a  dozen  conical  bundles  of  uriniferous  tubules,  each  bun- 
dle forming  what  is  called  a  pyramid.  The  upper  part  of  the  ureter,  or  duct 
of  the  organ,  is  dilated  into  the  pelvis ;  and  this,  again,  after  separating  into 
two  or  three  principal  divisions,  is  finally  subdivided  into  8  to  12  smaller 
portions,  calyces,  each  of  which  receives  the  pointed  extremity  or  papilla  of 
a  pyramid.  Sometimes,  however,  more  than  one  papilla  is  received  by  a 
calyx. 

The  kidney  is  a  compound  tubular  gland.  Both  its  cortical  and  ils  medul- 
lary portions  are  composed  essentially  of  numerous  tubes,  the  tubuli  urinijeri, 

371 


372 


EXCRETION 


which  begin  at  the  opening  on  the  Malpighian  pyramid  and,  after  a  devious 
course,  end  in  the  capsule  of  the  glomerulus. 

Tubuli  Uriniferi.  The  tubuli  uriniferi,  figure  287,  are  composed 
of  a  nearly  homogeneous  membrane,  and  are  lined  internally  by  epithelium. 
They  vary  considerably  in  size  in  different  parts  of  their  course,  but  are, 
on  an  average,  about  40  //.  in  diameter,  and  are  found  to  be  made  up  of  several 
distinct  sections.     The  first  section  or  part  to   be   identified  is   the  Malpi- 


Fig.  286. — Longitudinal  Section  of  Kidney  through  Hilum.  a.  Cortical  pyramid;  b,  medullary 
ray;  c,  medulla;  d,  cortex;  e,  renal  calyx;  f,  hilum;  g,  ureter;  h,  renal  artery;  i,  obliquely  cut  tubules 
of  medulla;  j  and  k,  renal  arches;  /,  column  of  Bertini;  m,  connective  tissue  and  fat  surrounding 
renal  vessels;  n,  medulla  cut  obliquely;  o,  papilla;  p,  medullary  pyramid.     (Merkel-Henle.) 


ghian,  or  Bowman's,  capsule,  figure  287.  It  is  composed  of  a  hyaline  membrana 
propria,  thickened  by  a  varying  amount  of  fibrous  tissue,  and  lined  by  flattened 
nucleated  epithelial  plates.  This  capsule  is  the  dilated  extremity  of  the 
uriniferous  tubule  which  is  invaginated  to  receive  the  glomerulus  of  con- 
voluted capillary  blood-vessels.  The  invaginated  portion  of  the  tubule  is  of 
particular  importance  since  it  is  the  membrane  through  which  a  large  part 
of  the  urine  is  secreted.  The  glomerulus  is  connected  with  an  efferent  and 
an  afferent  blood-vessel.  The  Malpighian  capsule  is  connected  by  a  con- 
stricted neck,  figure  287,  N,  with  the  proximal  convoluted  tubule.     This  forms 


TUBULI     URINIFERI 


373 


several  distinct  curves  and  is  lined  with  short  columnar  cells.  The  tube 
next  passes  almost  vertically  downward  toward  the  medulla,  forming  the 
spiral  tubule,  still  within  the  cortex  of  the  kidney,  which  is  of  much  the  same 
diameter.  The  loop  of  Henle,  L,  in  the  medulla,  is  a  very  narrow  tube  lined 
with  flattened  nucleated  cells.     Passing  vertically  upward  from  the  loop  of 


COB  TEX 

i  ; 

IBYRINTH    ]it£.D.RAY\  LABYR. 


Fig.  287- — Scheme  of  Uriniferous Tubule  and  of  the  Blood-vessels  of  the  Kidney,  Showing  Their 
Relation  to  Each  Other  and  to  the  Different  Parts  of  the  Kidney.  G,  Glomerulus;  BC,  Bowman's 
capsule;  N,  neck,  PC,  proximal  convoluted  tubule;  S,  spiral  tubule;  D,  descending  arm  of  Henle's 
loop;  L,  Henle's  loop;  A ,  ascending  arm  of  Henle's  loop;  IDC,  distal  convoluted  tubule;  AC,  arched 
tubule;  SC,  straight  collecting  tubule;  ED,  duct  of  Bellini;  A,  arcuate  artery,  and  V,  arcuate  vein, 
giving  off  interlobular  vessels  to  cortex  and  vasa  recta  to  medulla;  a,  afferent  vessel  of  glomer- 
ulus; e,  efferent  vessel  of  glomerulus;  c,  capillary  network  in  cortical  labyrinth;  5,  stellate  veins,  vr, 
vasa  recta  and  capillary  network  of  medulla.      (Pearsol.) 

Henle,  the  tubule  varies  somewhat  in  histological  character,  but  the  irregular 
tubule  and  the  distal  convoluted  tube,  identical  in  all  respects  with  the  prox- 
imal convoluted  tube,  are  to  be  noted.  The  proximal  convoluted  tube 
passes  into  the  curved  and  straight  collecting  tubes,  the  latter  running 
vertically  downward  to  the  papillary  layer,  and,  joining  with  other  collecting 
tubes,  form  larger  ducts  which  finally  open  at  the  apex  of  the  papilla.  These 
collecting  tubes  are  lined  with  nucleated  columnar  or  cubical  cells. 


:;7i 


EXCRETION 


Renal  Blood  Supply.  The  renal  artery  divides  into  several  branches 
which  pass  in  at  the  hilus  of  the  kidney  and  are  covered  by  a  fine  sheath 
<if  areolar  tissue  derived  from  the  capsule.  They  enter  the  substance  of  the 
organ  chiellv  in  the  intervals  between  the  papillae  and  at  the  junction  between 
the  cortex  and  the  boundary  Layer.  The  main  branches  then  pass  almost 
horizontally,  forming  more  or  less  complete  arches  and  giving  off  branches 
upward  to  the  cortex  and  downward  to  the  medulla.  The  former  are  for 
the  most  part  straight;  they  pass  almost  vertically  to  the  surface  of  the  kidney, 
giving  off  laterally  in  all  directions  longer  and  shorter  branches,  which  ulti- 


Fig.  288. — From  a  Vertical  Section  through  the  Kidney  of  a  Dog,  the  Capsule  of  which  is  Sup- 
posed to  be  on  the  Right,  a,  The  capillaries  of  the  Malpighian  capsule,  the  glomerulus,  are  arranged 
in  lobules;  n,  neck  of  capsule;  c,  convoluted  tubes  cut  in  various  directions;  b,  irregular  tubule: 
d,  e,  and  f  are  straight  tubes  running  toward  capsules  forming  a  so-called  medullary  ray;  d,  collect- 
ing tube;  e,  spiral  tube;  /,  narrow  section  of  ascending  limb.     X  380.     (Klein  and  Noble  Smith. )J 


mately  supply  the  glomerulus.  The  small  afferent  artery,  figures  287,  a, 
290,  d,  which  enters  the  Malpighian  capsule,  breaks  up  in  the  interior  into 
a  dense  convoluted  and  looped  capillary  plexus,  which  is  ultimately  gathered 
up  again  into  several  small  efferent  vessels,  comparable  to  minute  veins, 
which  leave  the  capsule  at  one  or  more  places  near  the  point  at  which  the 
afferent  artery  enters  it.  On  leaving,  they  do  not  immediately  join  other 
small  veins  as  might  have  been  expected,  but  again  break  up  into  a  second 
set  of  capillary  vessels  which  form  an  interlacing  network  around  the  urinif- 
erous  tubules.  This  second  capillary  plexus  terminates  in  small  veins 
which,  by  union  with  others,  help  to  form  the  radicles  of  the  renal  vein. 


RENAL  BLOOD  SUPPLY 


375 


These  form  venous  arches  corresponding  to  the  arterial  arches  situated 
between  the  medulla   and  cortex. 

Thus,  in  the  kidney,  the  blood  entering  by  the  renal  artery  traverses 
two  sets  of  capillaries  before  emerging  by  the  renal  vein,  an  arrangement 
which  may  be  compared  to  the  portal  system. 

The  tuft  of  vessels  within  the  Malpighian  capsule  in  the  course  of  de- 
velopment has  been  thrust  into  the  dilated  extremity  of  the  urinary  tubule, 
which  finally  completely  invests  it.  Thus  within  the  Malpighian  capsule 
there  are  two  layers  of  squamous  epithelium,  a  parietal  layer  lining  the  cap- 
sule proper,  and  a  visceral  or  reflected  layer  immediately  covering  the  vas- 
cular tuft,  figure  290,  and  sometimes  dipping  down  into  its  interstices.     This 


1  Wt&'&X^v  ■ 


r 


Fig.  289. — Transverse  Section  of  a  Renal  Papilla,  a.  Large  tubes  or  papillary  ducts;  b,  c,  and 
d,  smaller  tubes  of  Henle;  e,  f,  blood  capillaries,  distinguished  by  their  flatter  epithelium. 
(Cadiat.) 

reflected  layer  of  epithelium  is  readily  seen  in  young  subjects,  but  cannot 
always  be  demonstrated  in  the  adult,  figures  290  and  291. 

The  vessels  which  enter  the  medullary  layer  break  up  into  smaller  arte- 
rioles, which  form  a  fine  arterial  meshwork  around  the  tubes  of  the  papillary 
layer  and  end  in  a  similar  plexus  from  which  the  venous  radicles  arise.  The 
vessels  do  not  form  a  double  set  of  capillaries. 

Besides  the  small  afferent  arteries  of  the  Malpighian  bodies  there  are, 
of  course,  others  which  are  distributed  in  the  ordinary  manner,  for  the  nutri- 
tion of  the  different  parts  of  the  organ;  and  there  are  numerous  straight 
vessels,  the  vasa  recta,  in  the  pyramids  between  the  tubes.  Some  of  these 
are  branches  of  the  vasa  efferentia  from  Malpighian  bodies,  and  therefore 
comparable  to  the  venous  plexus  around  the  tubules  in  the  cortical  portion, 
while  others  arise  directly  as  small  branches  of  the  renal  arteries. 


376 


EXCRETION 


Renal  Nerves.  Vasoconstrictor  and  vaso-dilator  nerves  are  sup- 
plied to  the  blood-vessels  of  the  kidney,  but  no  clearly  defined  secretory 
nerves  have  yet  been  demonstrated  for  the  organ.  The  vascular  nerves 
arise  out  of  the  anterior  spinal  roots  (Bradford),  chiefly  the  eleventh  to  the 


ui.  r  i  29°-—Malpighian  Capsule  and  Tuft  of  Capillaries,  Injected  through  the  Renal  Artery 
witn  colored  Lrelatin.  a,  Glomerular  vessels;  b,  capsule;  c,  anterior  capsule;  d,  glomerular  artery; 
e,  efferent  veins;  /.  epithelium  of  tubes.     (Cadiat.) 


Fig.  291.— Diagrams  Illustrating  Stages  in  the  Development  of  the  Malpighian  Capsule.  In  1 
and  2  the  developing  blood-vessel  is  approaching  the  blind  end  of  the  capsule.  In  3  the  tubule  is 
beginning  to  invagmate  and  enclose  the  capillary.  In  4  and  5  later  stages  are  shown.  The  cells 
forming  the  two  layers  of  the  capsule  grow  very  thin.     (Bailey.) 

thirteenth  dorsal  nerves.  They  reach  the  kidney  by  way  of  the  splanchnic 
nerves  and  the  renal  plexus  to  the  renal  artery  along  which  they  run  into 
the  substance  of  the  kidney.  Berkeley  has  demonstrated  nerve  plexuses 
about  the  arterioles  and  around  Bowman's  capsule.     Terminal  knob-like 


THE    URETERS    AND    URINARY    BLADDER  377 

endings  of  nerve  fibrils  were  shown.  Some  authors  have  claimed  renal  vaso- 
constriction following  vagus  stimulation,  but  the  fact  seems  not  to  be  uni- 
versally admitted. 

The  Ureters  and  Urinary  Bladder.  The  duct  of  each  kidney,  the 
ureter,  is  a  tube  about  the  size  of  a  goose-quill  and  from  twelve  to  sixteen 
inches  in  length.  It  is  continuous  above  with  the  pelvis  of  the  kidney,  and 
ends  below  by  obliquely  perforating  the  walls  of  the  bladder  and  opening 
on  its  internal  surface.  It  has  three  principal  coats,  an  outer  fibrous,  a 
middle  muscular,  of  which  the  fibers  are  unstriped  and  arranged  in  three 
layers.  The  fibers  of  the  central  layer  are  circular,  and  those  of  the  other 
two  layers  longitudinal  in  direction.  It  has  an  internal  mucous  lining  con- 
tinuous with  that  of  the  pelvis  of  the  kidney  above  and  the  lining  of  the  urinary 
bladder  below.  The  urinary  bladder,  which  forms  a  receptacle  for  the  tem- 
porary lodgment  of  the  urine  in  the  intervals  of  its  expulsion  from  the  body, 
is  more  or  less  pyriform.  Its  widest  part,  which  is  situated  above  and  be- 
hind, is  termed  the  fundus;  and  the  narrow  constricted  portion  in  front  and 
below,  by  which  it  becomes  continuous  with  the  urethra,  is  called  its  cervix 
or  neck.  It  is  constructed  of  four  principal  coats:  serous,  muscular,  areolar 
or  submucous,  and  mucous.  The  fibers  of  the  muscular  coat  deserve  special 
mention.  They  are  unstriped,  are  arranged  in  three  principal  layers,  of 
which  the  external  and  internal  have  a  general  longitudinal,  and  the  middle 
layer  a  circular,  direction.  The  latter  are  especially  developed  around  the 
cervix  of  the  organ,  and  are  described  as  forming  a  sphincter  vesicae.  The 
mucous  membrane  is  provided  with  mucous  glands,  which  are  more  numer- 
ous near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood-  and  lymph-vessels,  and  with 
nerves.  The  latter  are  from  the  sacral  plexus  (spinal)  and  hypogastric 
plexus  (sympathetic).  Ganglion-cells  are  found,  here  and  there,  in  the 
course  of  the  nerve  fibers. 

THE  URINE. 

Quantity  and  General  Properties.  Healthy  urine  is  a  perfectly 
transparent  amber-colored  liquid,  with  a  peculiar  but  not  disagreeable  odor, 
a  bitterish  salty  taste,  and  a  specific  gravity  of  from  1020  to  1025.  The  urine 
consists  of  water  holding  in  solution  certain  organic  and  saline  matters  as  its 
ordinary  constituents,  and  occasionally  various  other  matters.  Some  of  the 
latter  are  indications  of  diseased  states  of  the  system,  and  others  are  derived 
from  unusual  articles  of  food  or  drugs  taken  into  the  stomach. 

The  total  quantity  of  urine  passed  in  twenty-four  hours  is  influenced 
by  numerous  circumstances.  In  adults  of  average  size  and  medium  ac- 
tivity the  daily  amount  of  urine  may  be  given  as  from  1,200  c.c.  to  1,500  c.c. 
In  Chittenden's  recent  observations  on  nine  athletic  students  and  on  eight 


IO-635 


8.135 


3  78  EXCRETION 

soldiers  the  average  daily  output  of  urine  through  a  period  of  about  five 
months  was  for  the  students  1,215  c-c-  with  average  specific  gravity  of  1020, 
and  for  the  soldiers  1,042  c.c.  with  specific  gravity  of  1023. 

General  Chemical  Composition  of  the  Urine. 

Water 967 

Solids: 

Urea 14.230 

Other  nitrogenous  crystalline  bodies :  -\ 

Uric  acid,  principally  in  the  form  of  alkaline  Urates,  a  trace  j 

only  free 

Kreatinin,  Xanthin,  Hypoxanthin 

Hippuric  acid 

Mucus,  Pigments,  and  ferments 

Salts: 

Inorganic: 

Principally   Sulphates,  Phosphates,  and   Chlorides  of    So- 
dium and  Potassium,  with  Phosphates  of  Magnesium 

and  Calcium,  traces  of  Silicates 

Organic: 

Lactates,    Hippurates,    Oxalates,   Acetates,  and   Formates,   I 

which  appear  only  occasionally J  33 

Sugar a  trace  sometimes. 

Gases  (nitrogen  and  carbonic  acid  principally).  ■ 


Reaction.  The  normal  reaction  of  the  urine  is  slightly  acid.  This 
acidity  is  due  to  carbonic  acid  and  to  acid  phosphate  of  sodium,  and  is  less 
marked  soon  after  meals.  After  standing  for  some  time  the  acidity  increases 
from  a  kind  of  acid  fermentation,  due  in  all  probability  to  the  presence  of 
mucus  and  fungi,  and  acid  urates  or  free  uric  acid  is  deposited.  After  a 
time,  varying  in  length  according  to  the  temperature,  the  reaction  becomes 
strongly  alkaline  from  the  change  of  urea  into  ammonium  carbonate,  due 
to  the  presence  of  one  or  more  specific  micro-organisms  (micrococcus  urece). 
In  the  process  of  fermentation  the  urea  takes  up  two  molecules  of  water,  a 
strong  ammoniacal  and  fetid  odor  appears,  and  there  are  deposits  of  triple 
phosphates  and  alkaline  urates.  This  does  not  occur  unless  the  urine  is 
freely  exposed  to  the  air,  or,  at  least,  until  air  has  had  access  to  it. 

In  most  herbivorous  animals  the  urine  is  alkaline  and  turbid.  The 
difference  depends  not  on  any  peculiarity  in  the  mode  of  secretion,  but  on 
the  difference  in  the  food  on  which  the  two  classes  of  animals  subsist;  for 
when  carnivorous  animals,  such  as  dogs,  are  restricted  to  a  vegetable  diet, 
their  urine  becomes  pale,  turbid,  and  alkaline  like  that  of  herbivorous 
animals,  while  the  urine  voided  by  the  Herbivora,  e.g.,  rabbits,  fed  for 
some  time  exclusively  upon  animal  substances,  presents  the  acid  reaction  and 
other  qualities  of  the  urine  of  Carnivora,  and  its  ordinary  alkalinity  is  again 
restored  only  o»  the  substitution  of  a  vegetable  for  the  animal  diet.  Human 
urine  is  not  usually  rendered  alkaline  by  vegetable  diet,  but  it  becomes  so 


SPECIFIC    GRAVITY    OF    URINE  379 

after  the  free  use  of  alkaline  medicines,  or  of  the  alkaline  salts  with  carbonic 
or  vegetable  acids;  for  these  latter  are  changed  into  alkaline  carbonates 
previous  to  elimination  by  the  kidneys. 

Specific  Gravity  of  Urine.  The  average  specific  gravity  of  the  human 
urine  is  about  1020  to  1025.  The  relative  quantity  of  water  and  of  solid 
constituents  of  which  it  is  composed  is  materially  influenced  by  the  condition 
and  occupation  of  the  body  during  the  time  at  which  it  is  secreted;  by  the 
length  cf  time  which  has  elapsed  since  the  last  meal;  by  the  amount  of  water 
taken;  and  by  several  other  less  important  circumstances.  The  morning 
urine  is  the  best  adapted  for  analysis  in  health,  since  it  represents  the  simple 
secretion  unmixed  with  the  elements  of  food  or  drink.  If  it  is  not  used  the 
whole  of  the  urine  passed  during  a  period  of  twenty-four  hours  should  be 
taken.  The  specific  gravity  of  the  urine  may  thus,  consistently  with  health, 
range  widely  on  both  sides  of  the  usual  average.  It  may  vary  from  1015 
in  the  winter  to  1025  in  the  summer;  but  variations  of  diet  and  exercise, 
and  many  other  circumstances,  may  make  even  greater  differences  than 
these.  The  variations  may  be  extreme  in  disease,  sometimes  decreasing 
in  albuminuria  to  1004,  and  frequently  increasing  in  diabetes,  when  the 
urine  is  loaded  with  sugar,  to  1050  or  even  to  1060. 

Average  Daily  Quantity  of  the  Chief  Urinary  Constituents.    (Modified  from 

Parkes.) 

Per  Kilo  of 
Body  Weight. 

Water 1,500.    c.c.  23 .0000  grams 

Solids 72.         grams  0.8800      " 

Urea 33.180      "  .5000      " 

Kreatinin .910      "  .0140      " 

Uric  Acid .555      "  .0084      " 

Hippuric   Acid .400      "  .0060      " 

Pigment  and  Extractives 10.000       "  .1510      " 

Sulphuric  Acid 2.012      "  .0480      " 

Phosphoric  Acid 3-I04      "  -°3°5      " 

Chlorine 7.000       "  .1260       " 

Ammonia -77°      " 

Potassium 2 .  500      " 

Sodium 11.090      " 

Calcium .260      :< 

Magnesium .  207      " 

Variations  in  the  Constituents  of  Urine.  Most  of  the  constituents 
are,  even  in  health,  liable  to  variations  from  the  proportions  given  in  the 
above  table.  The  variations  of  the  quantity  of  water  in  different  seasons, 
and  according  to  the  quantity  of  drink  and  exercise,  have  just  been  men- 
tioned. The  water  of  the  urine  is  also  liable  to  be  influenced  by  the  condi- 
tion of  the  nervous  system,  being  sometimes  greatly  increased,  e.g.,  in  hysteria 
and  in  some  other  nervous  affections,  and  at  other  times  diminished.  The 
increase  in  water  may  be  either  attended  with  an  augmented  quantity  of 
solid  matter  in  some  diseases,  as  in  ordinary  diabetes,  or  may  be  nearly  the  sole 


380 


excrpttion 


change,  as  in  the  affection  termed  diabetes  insipidus.  A  febrile  condition 
almost  always  diminishes  the  quantity  of  water;  and  a  like  diminution  is  caused 
by  any  affection  which  draws  off  a  large  quantity  of  fluid  from  the  body 
through  any  other  channel  than  that  of  the  kidneys,  e.g.,  the  bowels  or  the  skin. 

In  disease  or  after  the  ingestion  of  special  foods,  various  abnormal  sub- 
stances occur  in  urine,  of  which  the  following  may  be  mentioned.  Serum- 
albumin,  Globulin,  Ferments  (apparently  present  in  health  also),  Proteoses, 
Blood,  Sugar,  Bile  acids  and  pigments,  Casts,  Fats,  various  Salts  taken  as 
foods  or  as  medicines,  Micro-organisms  of  various  kinds. 

The  Nitrogenous  Substances  in  Urine.  The  nitrogenous  waste  prod- 
ucts which  are  formed  in  the  body  in  the  metabolism  of  the  proteid  foods 
are  ultimately  eliminated  chiefly  through  the  kidney,  to  some  extent  through 
the  bowel,  and  slightly  through  the  skin.  The  total  nitrogen  in  the  urine 
and  in  the  feces  multiplied  by  the  factor  6.25  is  a  measure  of  the  nitrogenous 


Fig.  292. — Crystals  of  Urea. 

foods,  i.e.,  proteids,  metabolized  by  the  body.  The  nitrogen  excreted  in  the 
urine  is  in  the  form  of  urea  87.5  per  cent,  ammonia  4.3  per  cent,  kreatinin 
3.6  per  cent,  uric  acid  0.8  per  cent,  and  undetermined  forms  3.73  per  cent, 
according  to  Folin.  The  total  quantity  of  nitrogen  eliminated  in  all  these 
forms  per  day  is  given  as  about  18  grams.  In  Chittenden's  recent  experi- 
ments this  quantity  is  reduced  to  as  low  as  6  grams  or  even  less  per  day. 

Urea.  Urea,  CON2H4,  is  the  principal  solid  constituent  of  the  urine, 
forming  nearly  one-half  of  the  total  quantity.  It  is  also  the  most  important 
ingredient,  since  it  is  the  chief  form  in  which  the  waste  nitrogen  which  is 
derived  from  proteid  metabolism  is  excreted  from  the  body. 

Properties.  Urea,  like  other  solid  constituents  of  the  urine,  exists  in  a 
state  of  solution.  When  in  the  solid  state,  it  appears  in  the  form  of  delicate 
silvery  acicular  crystals,  which,  under  the  microscope,  are  seen  as  four- 
sided  prisms,  figure  292.  It  readily  combines  with  some  acids,  like  a  weak 
base,  and  may  thus  be  conveniently  procured  in  the  form  of  crystals  of  nitrate 
or  oxalate  of  urea,  figures  293  and  294. 


THE    FORMATION    OF    UREA  381 

Urea  is  colorless  when  pure;  when  impure  it  may  be  yellow  or  brown. 
It  is  without  smell  and  of  a  cooling  niter-like  taste.  It  has  neither  an  acid 
nor  an  alkaline  reaction,  and  deliquesces  in  a  moist  and  warm  atmosphere. 
At  1 50  C.  it  requires  for  its  solution  less  than  its  own  weight  of  water.  It  is 
soluble  in  all  proportions  of  boiling  water,  and  requires  five  times  its  weight 
of  cold  alcohol  for  its  solution.  It  is  insoluble  in  ether.  At  1200  C.  it  melts 
without  undergoing  decomposition;  and  at  a  still  higher  temperature  ebulli- 
tion takes  place,  and  carbonate  of  ammonium  sublimes. 

Urea  is  decomposed  by  sodium  hypochlorite  of  hypobromite  or  by  nitrous 
acid,  with  evolution  of  nitrogen.  It  forms  compounds  with  acids,  of  which 
the  chief  are  urea  hydrochloride,  CON2H4.HCL;  urea  nitrate,  CON,H4.- 
HN03;    and  urea  phosphate,   CON2H4.H3P04.     It  forms  compounds  with 


Fig.  293. — Crystals  of  Urea  Nitrate.  Fig.  294.— Crystals  of  Urea  Oxalate. 

metals  such  as  HgO.CON,H4,  with  silver,  CON2H2Agr  Urea  is  isomeric 
with  ammonium  cyanate,  NH4CNO,  and  was  first  prepared  artificially  from 
that  substance. 

The  Formation  of  Urea.  Proteids  in  the  body  have  their  nitrog- 
enous moiety  broken  down  to  ammonia,  by  what  Folin  considers  essentially 
a  series  of  hydrolytic  cleavages,  which  is  then  built  up  into  urea,  as  described 
more  fully  in  the  chapter  on  Metabolism.  This  last  step  is  essentially  a 
synthetic  process  which,  from  the  fact  that  ammonium  carbonate  introduced 
into  the  blood  is  eliminated  as  urea,  may  be  supposed  to  occur  as  follows: 

NH2  NH2 

/  / 
CO          —  H,0          =CO 

\  \ 

ONH4  NH2 

Ammonium 

Carbamate  Urea 

Urea  is  present  in  varying  amounts  in  all  organs  and  fluids  of  the  body,  as 
shown  by  the  following  determinations  of  Schoendorff  on  the  dog: 

Per  cent  of 
Organ.  Urea. 

Blood 0.1 16 

Muscle 0.080 

Kidney 0.670 

Liver 0.112 

Heart o .  1 73 

Brain 0.128 

Spleen 0.122 


382  EXCRETION 

It  has  been  proven  that  the  kidney  does  not  form  urea;  in  fact  the  kid- 
neys may  be  removed  from  the  body,  and  urea  will  continue  to  accumulate 
in  the  blood.  Urea  is  formed  chiefly  in  the  liver,  but  may  in  part  be  con- 
structed in  other  organs,  as  described  more  fully  on  page  411.  It  follows 
that  the  kidney  is  only  the  channel  for  the  elimination  of  this  nitrogenous 
compound. 

Decomposition  of  the  urea  with  development  of  ammonium  carbonate 
takes  place  from  the  action  of  bacteria  (micrococcus  ureae)  when  urine  is 
kept  for  some  days  after  being  voided,  which  explains  the  ammoniacal  odor 
then  evolved.  The  urea  is  sometimes  decomposed  before  it  leaves  the  bladder, 
when  the  mucous  membrane  is  diseased  and  the  mucus  secreted  by  it  is 
abundant:  but  decomposition  does  not  occur  unless  atmospheric  germs  have 
had  access  to  the  urine. 

Quantity  Excreted.  The  quantity  of  urea  excreted  is,  like  that  of  the  urine 
Itself,  subject  to  considerable  variation.  For  a  healthy  adult  about  30  grams 
j  er  day  may  be  taken  as  rather  a  high  average.  Its  percentage  in  healthy 
urine  is  from  2  to  2.5.  Its  amount  is  materially  influenced  by  diet,  being 
greater  on  a  diet  of  high  proteid  content.  The  quantity  of  urea  excreted 
by  children,  relatively  to  their  body -weight,  is  much  greater  than  by  adults; 
thus  the  quantity  of  urea  execreted  per  kilogram  of  weight  was  found  to  be, 
in  a  child,  0.8  gram;  in  an  adult  only  0.4  gram.  Regarded  in  this  way,  too, 
the  excretion  of  carbonic  acid  gives  similar  results,  the  proportions  in  the 
child  and  adult  being  as  82  to  34. 

Uric  Acid.  Uric  acid,  C5H4N403,  is  rarely  absent  from  the  urine 
of  man  or  animals,  though  in  the  feline  tribe  it  seems  to  be  sometimes  entirely 
replaced  by  urea.  In  birds  and  reptiles  uric  acid  or  its  salts  is  the  chief 
form  in  which  nitrogen  is  eliminated  from  the  body. 

Properties.  Uric  acid  is  a  colorless,  crystalline  compound  of  the  purin 
group,  figure  295.  It  is  odorless  and  tasteless.  It  is  very  slightly  soluble  in 
water,  quite  insoluble  in  alcohol  and  ether,  and  freely  soluble  in  solutions 
of  the  alkaline  carbonates  and  other  salts. 

A  study  of  the  elimination  of  nitrogen  in  birds,  i.e.,  geese,  has  shown  that 
uric  acid,  like  urea  in  mammals,  is  formed  largely  in  the  liver  from  antecedent 
proteid  nitrogen.  In  man  the  elimination  of  uric  acid  increases  or  decreases 
with  the  proteid  content  of  the  daily  diet.  It  does  not,  however,  follow  the 
variations  of  the  food  nitrogen  so  closely  as  in  the  case  of  urea.  Any  food 
with  a  rich  nuclein  content  increases  the  excretion  of  uric  acid.  This  ob- 
servation has  led  to  the  inference  that  uric-acid  nitrogen  is  derived  from 
nuclear  metabolism,  page  413. 

Other  representatives  of  the  purin  group  are  adenin,  guanin,  xanthin, 
hypoxanthin,  etc.     Chemically,  caffeine  from  coffee  is  a  trimethyl  xanthin. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine  is  that 
of  a  brownish  or  yellowish  powderv  substance,   consisting  of  granules  of 


HIPPURIC    ACID 


383 


ammonium  or  sodium  urate.  When  deposited  in  crystals,  it  is  most  fre- 
quently in  rhombic  or  diamond-shaped  laminae,  but  other  forms  are  not 
uncommon,  figure  295.  When  deposited  from  urine,  the  crystals  are  gener- 
ally more  or  less  deeply  colored,  from  being  combined  with  the  coloring 
principles  of  the  urine. 

Hippuric  Acid.  This  compound,  C9H9N03,  has  long  been  known 
to  exist  in  the  urine  of  herbivorous  animals  in  combination  with  soda.  It 
also  exists  naturally  in  the  urine  of  man,  in  a  quantity  equal  to  or  rather  ex 


Fig.  295. — Various  Forms  of  Uric  Acid  Crystals. 


Fig.  296. — Crystals  of  Hippuric  Acid. 


ceeding  that   of   the  uric  acid.     The  quantity  excreted   is   increased   by  a 
vegetable  diet. 

Hippuric  acid  appears  to  be  formed  in  the  body  from  benzoic  acid  or 
from  some  allied  substance.  The  benzoic  acid  unites  with  glycin,  and  hip- 
puric acid  and  water  are  formed  thus: 

C6H..COOH  -f  CH2.NH2.COOH  =  C6H5.CO.NH.CH2.COOH  +  H20. 

Benzoic  Acid  Glycin  Hippuric  Acid 

Hippuric  acid  is  the  one  substance  which  has  been  clearly  demonstrated 
to  be  formed  by  the  kidney  itself. 

Kreatinin.  This  substance  is  present  in  urine  in  a  remarkably 
constant  quantity,  as  shown  recently  by  Folin's  analyses.  Its  daily  excre- 
tion quantity  is  from  1  to  15  grams  according  to  the  amount  of  active  tissue 
in  the  individual.  It  is  of  especial  importance  as  a  measure  of  the  metab- 
olism of  muscle  protoplasm. 

Ammonia.  A  considerable  daily  quantity  of  ammonia  in  com- 
bination is  found  in  the  urine,  showing  that  this  is  an  important  method  of 
nitrogen  elimination. 

Pigments.  The  pigments  of  the  urine  are  the  following:  1,  Uro- 
chrome,  a  yellow  coloring  matter,  giving  no  absorption  band;  of  which 
but  little  is  known.  Urine  owes  its  yellow  color  mainly  to  the  presence  of 
this  body.  2,  Urobilin,  an  orange  pigment,  of  which  traces  may  be  found  in 
nearly  all  urines,  and  which  is  especially  abundant  in  the  urines  passed  by 


384 


EXCRETION 


febrile  patients.  It  is  characterized  by  a  well-marked  spectroscopic  ab- 
sorption band  at  the  junction  of  green  and  blue.  Those  who  believe  urobilin 
to  be  identical  with  hydrobilirubin  suppose  that  the  bilirubin  is  reduced  by 
the  putrefactive  processes  in  the  intestines,  and  is  conveyed  in  its  reduced 
form  by  the  blood  stream  to  the  kidneys.  3,  Uroerythrin,  occasionally  found. 
And,  4,  Uromelanin. 

Mucus.  Mucus  sediment  in  the  urine  consists  principally  of  the 
epithelial  debris  from  the  mucous  surface  of  the  urinary  passages.  Parti- 
cles of  epithelium,  in  greater  or  less  abundance,  may  be  detected  in  most 
samples  of  urine,  figure  297.  As  urine  cools,  the  mucus  is  sometimes  seen 
suspended  in  it  as  a  delicate  opaque  cloud,  but  generally  it  falls.     In  inflam- 


Fig.  297. 


Fig.  298. 


Fig.  297. — Urinary  Deposit  of  Mucus,  etc. 

Fig.  298. — Urinary  Sediment  of  Triple   Phosphates  (large   prismatic  crystals)   and   Urate  of 
Amonium,  from  urine  which  had  undergone  alkaline  fermentation. 


matory  affections  of  the  urinary  passages,  especially  of  the  bladder,  mucus 
is  secreted  in  large  quantities  and  speedily  undergoes  decomposition. 

Saline  Matter.  Sulphuric  acid,  in  the  form  of  salts,  is  taken  in 
very  small  quantity  with  food.  Sulphur  is  also  a  constituent  part  of  the 
proteid  molecule;  hence  its  elimination,  like  that  of  nitrogen,  gives  a  certain 
measure  of  proteid  metabolism.  It  is  excreted  as  inorganic  sulphates  of 
sodium  and  potassium,  and  as  ethereal  sulphates,  compounds  of  phenol, 
cresol,  skatol,  i.e.,  cresol  sulphuric  acid  (C7H?OS02OH),  etc. 

The  phosphoric  acid  in  the  urine  is  combined  partly  with  the  alkalies, 
partly  with  the  alkaline  earths — about  four  or  five  times  as  much  with  the 
former  as  with  the  latter.  In  blood,  saliva,  and  other  alkaline  fluids  of  the 
body  phosphates  exist  in  the  form  of  alkaline,  neutral,  or  acid  salts.  In  the 
urine  they  are  acid  salts,  viz.,  the  sodium,  ammonium,  calcium,  and  magne- 
sium phosphates,  the  excess  of  acid  being  (Liebig)  due  to  the  appropriation 
of  the  alkali  with  which  the  phosphoric  acid  in  the  blood  is  combined,  by  the 
several  new  acids  which  are  formed  or  discharged  at  the  kidneys,  namely  the 
uric,  hippuric,  and  sulphuric  acids,  all  of  which  are  neutralized  with  soda. 


OCCASIONAL   CONSTITUENTS    OF    URINE 


385 


The  phosphates  are  taken  largely  in  both  vegetable  and  animal  food. 
Some  are  excreted  at  once;  others  only  after  being  transformed  and  incor- 
porated with  the  tissues.  Calcium  and  magnesium  phosphates  form  the 
principal  earthy  constituents  of  bone,  and  from  the  decomposition  of  the 
osseous  tissue  the  urine  derives  a  quantity  of  this  salt.  The  decomposition  of 
other  tissues  also  furnishes  large  supplies  of  phosphorus  to  the  urine,  which 
phosphorus  is  supposed,  like  the  sulphur,  to  be  united  with  oxygen,  and  then 
combined  with  bases.  The  quantity  is,  however,  liable  to  considerable 
variation.  The  earthy  phosphates  are  more  abundant  after  meals,  whether 
of  animal  or  vegetable  food,  and  are  diminished  after  long  fasting.  The 
alkaline  phosphates  are  increased  after  animal  food,  diminished  after  vegetable 


Fig.  299- — Crystals  of  Cystin. 


Fig.  300. — Crystals  of  Calcium  Oxalate. 


food.  Phosphorus  uncombined  with  oxygen  appears,  like  sulphur,  to  be  ex- 
creted in  the  urine.  When  the  urine  undergoes  alkaline  fermentation  phos- 
phates are  deposited  in  the  form  of  a  urinary  sediment,  consisting  chiefly  of 
ammonio-magnesium  phosphates  (triple  phosphate),  figure  298. 

The  Chlorine  of  the  urine  occurs  chiefly  in  combination  with  sodium. 
Next  to  urea,  sodium  chloride  is  the  most  abundant  solid  constituent  of  the 
urine.  As  the  chlorides  exist  largely  in  food,  and  in  most  of  the  animal  fluids, 
their  occurrence  in  the  urine  is  easily  understood. 

Occasional  Constituents  of  Urine.  Cystin,  C3H7NS02,  figure  299, 
is  an  occasional  constituent  of  urine.  It  resembles  taurin  in  containing  a 
large  quantity  of  sulphur — more  than  25  per  cent.  It  does  not  exist  in 
healthy  urine. 

Another  common  morbid  constituent  of  the  urine  is  Oxalic  acid,  which  is 
frequently  deposited  in  combination  with  calcium,  figure  30c,  as  a  urinary 
sediment.  Like  cystin,  but  much  more  commonly,  it  is  the  chief  constituent 
of  certain  calculi. 

Dextrose  and  albumin  are  sometimes  present  in  pathological  urine,  and  are 
of  particular  interest  from  the  clinical  point  of  view.     See  the  subject  Gly- 
cosuria, page  418. 
25 


386  EXCRETION 

THE  METHOD  OF  EXCRETION  OF  URINE. 

The  secretion  of  urine  is  an  act  the  complexity  of  which  can  be  profitably 
discussed  only  after  a  clear  understanding  of  three  main  factors  which  have 
already  been  presented,  viz.,  the  chemical  composition  of  the  urine  secreted, 
the  structure  of  the  kidney  tubule  as  a  secreting  organ,  and,  finally,  the  chemi- 
cal composition  of  the  blood  which  supplies  the  materials  to  the  kidney  for 
the  formation  of  the  urine.  The  substances  found  in  the  urine  are  for  the 
most  part  also  to  be  found  in  the  blood-plasma.  But  the  relative  percentage 
composition  is  very  different.  The  amount  of  urea  in  the  blood  is  only  a 
fractional  part  as  concentrated  as  in  the  urine,  while  albumins  and  sugars, 
which  are  so  plentiful  in  the  blood,  are  normally  present  in  the  urine  only 
in  traces.  The  presence  of  the  glomerulus  with  its  special  vascular  supply, 
and  the  different  loops  of  the  tubule,  with  its  gland-like  epithelial  wall,  would, 
a  priori,  lead  one  to  suspect  special  functions  for  each. 

Theories  of  the  Secretion  of  Urine.  Bowman  in  1842,  wholly  on 
structural  grounds,  advanced  a  theory  of  urinary  secretion  which  has  more 
recently  been  restated  and  given  an  experimental  basis  by  Heidenhain.  This 
view  as  given  by  Heidenhain  is  as  follows: 

1,  The  secretion  in  the  kidney  depends  upon  the  physiological  activity  of 
special  secreting  cells  which  are  of  two  kinds.  2,  The  first  type  of  cell  is 
represented  by  the  single  layer  of  epithelium  covering  the  glomerular  capil- 
laries. These  cells  secrete  especially  water  and  salts.  3,  The  second  type  of 
cell  is  represented  by  the  gland-like  epithelial  cells  which  form  the  convo- 
luted tubules  and  the  loop  of  Henle.  These  cells  secrete  the  urea,  uric  acid, 
and  other  specific  constituents  of  the  urine.  4,  The  activity  of  each  kind  of 
cell  is  influenced  by  the  chemical  composition  of  the  blood  and  by  the  flow 
of  blood  through  the  kidney.  5,  The  relative  secretory  activity  of  the  glomer- 
ular cells  and  the  tubule  cells  is  sufficient  to  account  for  the  variation  in  the 
chemical  composition  of  the  urine. 

Ludwig  in  1844  advanced  a  strictly  mechanical  theory  of  urine  secretion 
based  on  his  own  experiments.  He  considered  the  glomerulus  and  Bowman's 
capsule  as  a  filtering  apparatus  in  which  substances  present  in  the  blood  are 
driven  through  the  epithelium  of  the  capsule  into  the  renal  tubule  by  the 
positive  pressure  of  the  blood  in  the  glomerular  capillaries.  This  very  dilute 
urine  in  the  capsule  is  supposed  to  be  concentrated  by  the  resorption  of  water 
as  it  flows  down  the  tubule.  Ludwig  originally  considered  this  resorption  of 
water  an  imbibition  process  in  which  the  greater  saturation  of  salts  in  the 
blood  caused  water  to  be  taken  up  through  the  renal  tubule  walls,  an  osmotic 
process.  At  present  most  observers  who  accept  the  view  that  filtration  takes 
place  at  the  glomerulus  explain  the  resorption  of  water  down  the  tubules  as 
an  act  of  cellular  resorption  or  secretion. 

Experimental  Observations.     There  are  numerous  nerves  to  the 


EXPERIMENTAL     OBSERVATIONS 


387 


kidney,  but  no  proven  secretory  influence  has  been  shown.  The  variations 
in  the  secretion  of  urine  that  follow  nervous  stimulation  are  quite  satisfactorily 
explained  by  the  changes  in  the  blood  flow. 

The  kidney  can  be  pLced  in  an  onkometer  and  its  variation  in  volume 
measured  directly,  figures  301  and  302.  This  volume  measurement,  when 
taken  with  the  arterial  pressure,  gives  a  very  good  index  of  the  volume  of 
blood  flowing  through  the  kidney.  Now  when  the  kidney  is  inserted  in  an 
onkometer  and  the  urine  collected  from  the  ureter,  it  is  found  in  general  that 
the  greater  the  pressure  and  flow  of  blood  the  greater  the  secretion  of  urine, 
as  would  follow  if  the  glomerulus  were  a  filtering  mechanism.  However,  if 
the  renal  vein  is  partially  obstructed,  even  though  the  blood  pressure  be  in- 
creased, the  amount  of  urine  secreted  is  sharply  decreased.     If  the  vein  is 


Fig.  301. — Diagram  of  Roy's  Onkometer.  a  Represents  the  kidney  enclosed  in  a  metal  box, 
which  opens  by  hinge  f;  b.  the  renal  vessels  and  ducts.  Surrounding  the  kidney  are  two  chambers 
formed  by  membranes,  the  edges  of  which  are  firmly  fixed  by  being  clamped  between  the  outside 
and  inside  metal  capsules  (the  latter  not  represented  in  the  figure),  the  two  being  firmly  screwed 
together  by  screws  at  h,  and  on  the  opposite  side.  The  membranous  chamber  below  is  filled  with  a 
varying  amount  of  warm  oil,  according  to  the  size  of  the  kidney  experimented  with,  through  the 
opening  then  closed  with  the  plug  *.  After  the  kidney  has  been  enclosed  in  the  capsule,  the  mem- 
branous chamber  above  is  filled  with  warm  oil  through  the  tube  e,  which  is  then  closed  by  a  tap 
(not  represented  in  the  diagram);  the  tube  d  communicates  with  a  recording  apparatus,  and  any 
alteration  in  the  volume  of  the  kidney  is  communicated  by  the  oil  in  the  tube  to  the  chamber  d 
of  the  Onkograph,  figure  302. 


completely  occluded,  the  secretion  of  urine  not  only  ceases  for  the  time  but 
does  not  immediately  begin  again  when  the  blood  pressure  and  flow  are  re- 
established. The  closure  of  the  vein  for  only  one  or  two  minutes  is  said  to 
stop  the  flow  of  urine  for  as  much  as  forty-five  minutes.  This  short  inter- 
ruption of  the  circulation  is  sufficient  to  bring  about  other  changes  in  the 
glomerular  epithelium,  for  it  now  excretes  albumin,  which  it  did  not  previously 
let  pass.  Therefore,  it  is  not  pressure  merely  that  favors  the  secretion,  but 
there  must  be  an  efficient  flow  of  blood.  The  secretion  is  influenced  espe- 
cially by  the  amount  of  blood  flowing  through  the  kidney  in  a  given  time. 


388 


EXCRETION 


In  the  frog  the  kidney  has  a  double  blood  supply.  The  renal  artery 
supplies  the  glomeruli,  while  a  branch  of  the  renal-portal  vein  supplies  the 
tubules.  Nussbaum  ligated  the  renal  artery  in  one  kidney  of  the  frog,  while 
leaving  the  circulation  of  the  other  kidney  undisturbed.  He  found  that  the 
operated  kidney  secreted  little  or  no  urine,  but  that  it  could  be  made  to  secrete 
by  injections  of  urea,  but  not  by  injections  of  albumin  or  sugar  as  in  the  nor- 
mal kidney.  Ligation  of  the  renal-portal  vein,  which  supplies  the  tubules 
in  the  frog,  caused  a  decrease  in  the  quantity  of  the  secretion,  whereas,  accord- 
ing to  Ludwig's  view,  it  ought  to  have  increased  the  quantity,  since  obviously 
resorption  could  not  take  place  with  any  degree  of  efficiency.  In  the  main, 
the  evidence  is  in  favor  of  the  view  that  even  the  glomerular  epithelium  does 


Fig.  302. — Roy's  Onkograph,  or  Apparatus  for  Recording  Alterations  in  the  Volume  of  the  Kid- 
ney, etc.,  as  shown  by  the  onkometer.  a.  Upright,  supporting  recording  lever  /,  which  is  raised  or 
lowered  by  the  needle  b,  which  works  through  f,  and  which  is  attached  to  the  piston  e,  working  in 
the  chamber  d,  with  which  the  tube  from  the  onkometer  communicates.  The  oil  is  prevented  from 
being  squeezed  out  as  the  piston  descends,  by  a  membrane,  which  is  clamped  between  the  ring- 
shaped  surfaces  of  the  cylinder  by  the  screw  *  working  upward;  the  tube  h  is  for  filling  the  instru- 
ment. 

not  filter  merely,  but  that  it,  as  living  protoplasm,  regulates  and  controls 
the  quantity  and  kind  of  material  passing  through  it. 

Micro-chemical  observations  have  been  enlisted  to  demonstrate  more  fully, 
if  possible,  the  activity  of  the  differen-  parts  of  the  epithelial  tubule.  Heiden- 
hain,  by  injections  of  indigo-blue  into  the  blood  stream,  followed  by  rapid 
fixation  of  the  kidney  in  alcohol  at  the  proper  stage  of  elimination,  has  de- 
monstrated crystals  of  the  pigment  in  the  renal  epithelial  cells  and  in  the 
lumen  of  the  tubule.  He  concluded  that  these  cells  were  actively  eliminating 
the  pigment  by  a  secretory  process.  This  observation  has  been  questioned. 
But  Heidenhain's  view  is  strengthened  by  Bowman's  observation  that  in  birds 
crystals  of  uric  acid  are  to  be  seen  in  the  cells  of  the  convoluted  tubules,  and 
in  the  lumen  adjacent. 

Only  traces  of  the  sugars  and  proteids  of  the  blood  are  found  in  normal 
urine,  but  when  either  cane  sugar,  peptone,  or  egg  albumin  is  introduced  into 
the  blood  it  is  rapidly  eliminated  by  the  kidney.     Egg  albumin  is  not  essen- 


DIURETICS 


389 


tially  different  from  the  serum  albumin  of  the  blood,  but  the  serum  albumin 
is  not  excreted.  These  are  both  non-dialyzable  compounds.  Sugar  and 
urea,  both  readily  dialyzable,  present  the  same  comparison,  i.e.,  urea  is  ex- 
creted, while  sugar  is  not.  If,  however,  the  percentage  of  sugar  is  high,  0.25 
per  cent  or  more,  it  is  then  eliminated.  The  excretion  of  the  highly  diffusible 
sodium  chloride  bears  a  similar  quantitative  relation  to  excretion.  If  present 
in  the  blood  in  relatively  low  amounts  it  is  not  secreted,  while  if  the  concentra- 
tion is  slightly  greater  it  may  be  quickly  eliminated.  Other  inorganic  salts, 
present  only  in  traces,  are  meanwhile  rapidly  eliminated.  Even  the  rapid 
elimination  of  a  slight  excess  of  water  in  the  blood  can  scarcely  be  explained 
on  purely  physical  grounds.  To  discharge  the  water  across  the  glomerulus 
from  the  blood  to  the  urine  requires  an  expenditure  of  osmotic  pressure  much 
greater  than  that  balanced  by  the  blood  pressure.  That  is,  the  epithelial  cells 
must  do  work,  and  the  energy  is  dependent  on  metabolism  in  the  cells.     At 


Fig.  303. — Curve  Taken  by  Renal   Onkometer  Compared  with  that  of  an  Ordinary  Blood- 
pressure  Curve,     a.  Kidney  curve;  b.  blood- pressure  curve.     (Roy.) 


least  one  substance,  hippuric  acid,  is  built  up  chemically  by  the  renal  cells 
and  secreted  as  such. 

It  would  seem,  therefore,  that  the  separation  of  urine  in  the  kidney  is  a 
secretory  process  dependent  on  the  protoplasmic  activity  of  the  living  renal 
cells,  that  the  apparent  selective  property  of  the  cells  is  a  manifestation  of 
such  activity,  and  that  even  water  is  secreted. 

Diuretics.  Certain  substances  increase  the  flow  of  urine  and  are 
called  diuretics.  They  act  directly  on  the  renal  epithelium,  for  example, 
urea,  or  indirectly  on  the  circulatory  system  to  increase  the  flow  of  blood. 
Digitalis  is  a  well-known  diuretic  which  increases  the  efficiency  of  the  circula- 
tion. It  also  stimulates  the  renal  epithelium  with  the  production  of  a  marked 
increase  in  the  flow  of  urine.  Caffeine  diuresis  can  best  be  explained  on  an 
assumed  stimulating  action  on  the  renal  epithelium.  Urea  introduced  into 
the  blood  produces  a  copious  secretion  of  urine.  Both  urea  and  the  saline 
diuretics  induce  a  flow  of  urine  out  of  all  proportion  to  the  osmotic  changes 
produced,  and  they  may  be  regarded  as  direct  stimulators  of  the  renal  epithe- 
lium. 


390  EXCRETION 

THE  DISCHARGE  OF  THE  URINE. 

As  each  portion  of  urine  is  secreted,  it  propels  that  which  is  already  in  the 
uriniferous  tubes  onward  into  the  pelvis  of  the  kidney.  Thence  it  passes 
through  the  ureter  into  the  bladder,  from  which  at  intervals  it  is  discharged 
to  the  exterior.  The  rate  and  mode  of  entrance  of  urine  into  the  bladder 
has  been  watched  in  cases  of  ectopia  vesica?,  i.e.,  cases  in  which  fissures  in 
the  anterior  or  lower  part  of  the  walls  of  the  abdomen  and  of  the  front  wall 
of  the  bladder  expose  to  view  the  orifices  of  the  ureters.  The  urine  does  not 
enter  the  bladder  at  any  regular  rate,  nor  is  there  a  synchronism  in  its  move- 
ment through  the  two  ureters.  Ordinarily  two  or  three  drops  enter  the 
bladder  every  minute,  each  drop  as  it  enters  first  raising  up  the  little  papilla 
on  which  the  ureter  opens,  and  then  passing  through  the  orifice,  which  at 
once  again  closes  like  a  sphincter.  Its  flow  is  aided  by  the  peristaltic  con- 
tractions of  the  ureters,  and  is  increased  in  deep  inspiration  or  by  straining. 
The  urine  collected  in  the  bladder  is  prevented  from  regurgitation  into  the 
ureters  by  the  mode  in  which  these  pass  through  the  walls  of  the  bladder, 
namely,  by  their  lying  a  half  to  three-quarters  of  an  inch  between  the  muscu- 
lar and  mucous  coats  before  they  turn  rather  abruptly  forward  and  open 
through  the  latter  into  the  interior  of  the  bladder. 

Micturition.  The  contraction  of  the  muscular  walls  of  the  bladder 
may  by  itself  expel  the  urine  with  little  or  no  help  from  other  muscles.  The 
vesicular  pressure  is  increased  in  the  voluntary  act  by  the  contraction  of 
the  abdominal  and  other  expiratory  muscles  which  bear  on  the  abdominal 
viscera,  thus  aiding  in  the  expulsion  of  the  contents  of  the  bladder.  The 
diaphragm  is  at  the  same  time  fixed  in  contraction  and  the  sphincter  of  the 
bladder  relaxes.  The  pressure  within  the  bladder  under  the  combined  con- 
tractions of  these  expulsive  muscles  sometimes  amounts  to  8  to  10  cm.  of 
mercury.  The  act  is  completed  by  the  accelerator  urinae  muscle,  which,  as 
its  name  implies,  quickens  the  stream  and  expels  the  last  drop  of  urine  from 
the  urethra.  The  act  is  under  the  regulative  control  of  a  nervous  center  in 
the  lumbar  spinal  cord,  through  which,  as  in  the  case  of  the  similar  center  for 
defecation,  the  various  muscles  concerned  are  coordinated  in  their  action. 
It  is  well  known  that  the  act  may  be  reflexly  induced,  e.g.,  in  children  who 
suffer  from  intestinal  worms  or  other  such  irritation.  Generally  the  afferent 
impulses  which  set  up  the  reflexes  leading  to  the  desire  to  micturate  are  ex- 
cited by  overdistention  of  the  bladder,  or  sometimes  by  a  few  drops  of  urine 
passing  into  the  urethra.  This  impulse  passes  up  to  the  lumbar  center  or 
centers,  and  reflexly  produces  on  the  one  hand  inhibition  of  the  sphincter 
and  on  the  other  contraction  of  the  necessary  muscles  for  the  expulsion 
of  the  contents  of  the  bladder.  In  the  voluntary  act  these  motor  centers 
are  stimulated  to  activity  by  impulses  coming  from  the  higher  cerebral 
centers. 


STRUCTURE    AND    FUNCTIONS    OF   THE    SKIN 


391 


THE  STRUCTURE  AND  EXCRETORY  FUNCTIONS  OF  THE  SKIN. 

The  skin  serves,  i,  as  an  external  integument  for  the  protection  of  the 
deeper  tissues,  and  2,  as  a  sensitive  organ  in  the  exercise  of  touch,  a  subject 
to  be  considered  in  the  chapter  on  the  Special  Senses.  It  is  also,  3,  an  im- 
portant secretory  and  excretory  organ;  and  4,  an  absorbing  organ.  5,  It 
plays  an  important  part  in  the  regulation  of  the  temperature  of  the  body  by 
controlling  the  loss  of  heat,  i.e.,  a  temperature-regulating  function,  discussed 
in  the  chapter  on  Animal  Heat. 

Structure.  The  skin  consists  principally  of  a  vascular  tissue  named 
the  corium,  derma,  or  cutis  vera,  and  of  an  external  covering  of  epithe- 
lium termed  the  epidermis  or  cuticle.  Within  and  beneath  the  corium  are 
embedded  several  organs  with  special  functions,  namely,  sudoriferous  glands, 


Fig.  304. — Vertical  Section  of  the  Epidermis  of  the  Prepuce,  a,  Stratum  correum,  of  very  few 
layers,  the  stratum  lucidum  and  stratum  granulosum  not  being  distinctly  represented;  b,  c,  d,  and 
e,  the  layers  of  the  stratum  Malpighii,  a  certain  number  of  the  cells  in  layers,  d,  and  e  showing  signs 
of  segmentation;  layer  c ,  consists  chiefly  of  prickle  or  ridge  and  furrow  cells;  /,  basement  membrane; 
g,  cells  in  cutis  vera.      (Cadiat.) 


sebaceous  glands,  and  hair  follicles ;  and  on  its  surface  are  sensitive  papilla:. 
The  so-called  appendages  of  the  skin — the  hair  and  nails — are  modifications 
of  the  epidermis. 

The  epidermis  is  composed  of  several  strata  of  cells  of  various  shapes  and 
sizes;  it  closely  resembles  in  its  structure  the  epithelium  of  the  mucous  mem- 
brane that  lines  the  mouth  or  covers  the  cornea.  The  following  four  layers 
may  be  distinguished: 


392 


EXCRETION 


The  Stratum  lucidum,  a  bright  homogeneous  membrane,  consisting  of 
squamous  cells  closely  arranged,  in  some  of  which  a  nucleus  can  be  seen. 
Stratum  granulosum,  consisting  of  one  layer  of  flattened,  fusiform,  distinctly 
nucleated  cells.  Stratum  Malpighii  or  Rete  mucosum  consists  of  many  strata 
of  cells.  The  deepest  cells,  placed  immediately  above  the  cutis  vera,  are 
columnar  with  oval  nuclei,  succeeded  by  a  number  of  layers  of  more  or  less 


Fig.  305. — Vertical  Section  of  Skin.  A,  Sebaceous  gland  opening  into  hair  follicle;  B,  mus- 
cular fibers;  C,  sudoriferous  or  sweat  gland;  D,  subcutaneous  fat;  E,  fundus  of  hair-follicle, 
with  hair-papillffi.      (Klein.) 


polyhedral  cells  with  spherical  nuclei;  the  more  superficial  layers  are  con- 
siderably flattened.  The  deeper  surface  of  the  rete  mucosum  is  accurately 
adapted  to  the  papilla?  of  the  true  skin,  being,  as  it  were,  moulded  on  them. 
It  is  very  constant  in  thickness  in  all  parts  of  the  skin.  The  cells  of  the  middle 
layers  of  the  stratum  Malpighii  are  connected  by  processes,  and  thus  form 
prickle  cells,  figure  28.  The  pigment  of  the  skin,  in  the  deeper  cells  of  rete 
mucosum,  causes  the  various  tints  observed  in  different  individuals  and  differ- 
ent races.     The  epidermis  maintains  its  thickness  in  spite  of  the  constant  wear 


GLANDS    OF   THE    SKIN  393 

and  tear  to  which  it  is  subjected.  The  columnar  cells  of  the  deepest  layer 
of  the  rete  mucosum  elongate,  multiply  by  division,  the  new  cells  produced 
being  pushed  toward  the  free  surface  of  the  skin.  There  is  thus  a  constant 
production  of  fresh  cells  in  the  deeper  layers,  and  a  constant  throwing  off  of 
old  ones  from  the  free  surface.  When  these  two  processes  are  accurately 
balanced,  the  epidermis  maintains  its  thickness.  When  by  intermittent 
pressure  a  more  active  cell-growth  is  stimulated,  the  production  of  cells  ex- 
ceeds their  waste  and  the  epidermis  increases  in  thickness,  as  we  see  in  the 
horny  hands  of  the  laborer. 

The  dermis,  or  cutis  vera  or  true  skin,  is  a  dense  and  tough,  but  yielding 
and  highly  elastic  structure  supporting  the  epidermis.  It  is  composed  of 
areolar  connective  tissue  interwoven  in  all  directions  and  forming  numerous 
spaces  by  its  interlacements.  These  areohe  in  the  deeper  layers  of  the  cutis 
are   usually  filled  with   little  masses  of  fat,  figure  305.     Unstriped  muscu- 


Fig.  306. — Terminal  Tubules  of  Sudoriferous  Glands,  Cut    in  Various  Directions.    From  the 
skin  of  the  pig's  ear.      (V.  D.  Harris.) 

lar  fibers  are  also  abundantly  present,  especially  in  the  skin  of  animals  which 
erect  the  hairs  with  greater  ease  than  is  usually  the  case  with  man. 

There  is  a  rich  network  of  blood-vessels  to  the  dermis.  In  the  dermal 
papilla?  and  about  the  sweat  glands  there  are  special  loops  of  capillaries. 
Nerve  fibers  are  also  distributed  to  the  papillae. 

The  special  nerve  terminations  in  the  skin  have  been  described  on  page  72. 

Glands  of  the  Skin.  The  skin  possesses  glands  of  two  kinds: 
Sudoriferous  or  Sweat  Glands,  and  the  Sebaceous  or  Oil  Glands. 

A  Sudoriferous  or  Sweat  Gland  consists  of  a  small  lobular  mass,  formed 
of  a  coil  of  tubular  gland-duct,  surrounded  by  blood-vessels,  and  embedded 
in  the  subcutaneous  adipose  tissue,  figure  305,  C.  The  duct  ascends  from 
this  coiled  mass  for  a  short  distance  in  a  spiral  manner  through  the  cutis 
and  the  epidermis,  and  then  opens  on  the  surface  of  the  skin.  In  the 
parts  where  the  epidermis  is  thin,  the  ducts  themselves  are  thinner  and 
more  nearly  straight  in  their  course. 


394  EXCRETION 

The  duct  is  lined  with  a  layer  of  columnar  epithelium  continuous  with 
the  epidermis.  The  coiled  or  secreting  portion  of  the  gland  is  lined  with 
at  least  two  layers  of  short  columnar  cells  with  very  distinct  nuclei,  figure  306. 
The  lumen  is  distinctly  bounded  by  a  special  lining  of  cuticle. 

The  sudoriferous  glands  are  abundantly  distributed  over  the  whole  sur- 
face of  the  body;  but  are  especially  numerous,  as  well  as  very  large,  in  the 
skin  of  the  palm  of  the  hand  and  of  the  sole  of  the  foot.  The  glands  by 
which  the  peculiarly  odorous  matter  of  the  axillae  and  groin  is  secreted  form 
a  nearly  complete  layer  under  the  cutis,  and  are  like  the  ordinary  sudoriferous 
glands,  except  in  being  larger  and  having  very  short  ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the  external 
auditory  passage  is  named  cerumen,  and  the  glands  themselves  ceruminons 
glands;  but  they  do  not  much  differ  in  structure  from  the  ordinary  sudorif- 
erous glands. 

The  sebaceous  glands,  figures  305  and  306,  like  sudoriferous  glands,  are 
abundant  in  most  parts  of  the  surface  of  the  body,  particularly  in  parts  largely 


Fig.  307. — Sebaceous  Gland  from  Human  Skin.     (Klein  and  Noble  Smith.) 

supplied  with  hair,  as  the  scalp  and  face.  They  are  thickly  distributed  about 
the  entrances  of  the  various  passages  into  the  body,  as  the  anus,  nose,  lips, 
and  external  ear.  They  are  entirely  absent  from  the  palmar  surface  of  the 
hand  and  the  plantar  surface  of  the  foot.  They  are  racemose  glands  com- 
posed of  an  aggregate  of  small  tubes  or  sacculi  lined  with  columnar  epithelium 


EXCRETORY    FUNCTION    OF   THE    SKIN  395 

and  filled  with  an  opaque  white  substance,  like  soft  ointment,  which  consists 
of  broken-up  epithelial  cells  which  have  undergone  fatty  degeneration.  Mi- 
nute capillary  vessels  overspread  them;  and  their  ducts  open  on  either  the 
surface  of  the  skin,  close  to  the  hair,  or,  which  is  more  usual,  directly  into 
the  follicle  of  the  hair.  In  the  latter  case,  there  are  generally  two  or  more 
glands  to  each  hair,  figure  306. 

The  story  of  the  structure  and  development  of  such  epithelial  struc- 
tures as  the  hair  and  the  nails  is  best  left  to  the  histologist,  to  whom  the 
student  is  referred. 

The  Excretory  Function  of  the  Skin.  The  function  of  the  skin 
which  is  of  special  interest  to  this  chapter  is  that  of  the  excretion  of  the  sweat. 
The  fluid  secreted  by  the  sweat  glands  is  usually  formed  so  gradually  that 
the  watery  portion  of  it  escapes  by  evaporation  as  fast  as  it  reaches  the  surface. 
But  during  strong  exercise,  exposure  to  great  external  warmth,  in  some 
diseases,  and  when  evaporation  is  prevented,  the  secretion  becomes  more 
sensible  and  collects  on  the  skin  in  the  form  of  drops  of  fluid. 

The  perspiration,  as  the  term  is  sometimes  employed  in  physiology,  in- 
cludes all  that  portion  of  the  secretions  and  exudations  from  the  skin  which 
are  thrown  on  the  surface  by  the  sweat  glands.  As  a  matter  of  fact,  this  is 
mingled  with  various  substances  lying  on  the  surface  of  the  skin.  The  con- 
tents of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  form  of  vapor, 
such  as  carbonic  acid  and  water,  and  in  part  other  matters  which  are  depos- 
ited on  the  skin,  and  mixed  with  the  sebaceous  secretions. 

The  secretion  of  the  sebaceous  glands  and  hair-follicles  consists  of  cast- 
off  epithelium  cells,  with  nuclei  and  granules,  together  with  an  oily  matter, 
extractive  matter,  and  stearin.  In  certain  parts,  also,  it  is  mixed  with  a 
peculiar  odorous  principle,  which  contains  caproic,  butyric,  and  rutic  acids. 
It  is  similar  in  composition  to  the  unctuous  coating,  or  vernix  caseosa,  which 
is  formed  on  the  body  of  the  fetus  while  in  the  uterus,  and  which  contains 
ordinary  fat.  This  sebaceous  secretion  serves  the  purpose  of  keeping  the 
skin  moist  and  supple,  and,  by  its  oily  nature,  of  both  hindering  the  evapora- 
tion from  the  surface  and  guarding  the  skin  from  the  effects  of  the  long-con- 
tinued action  of  moisture.  But  while  it  thus  serves  local  purposes,  its  re- 
moval from  the  body  entitles  it  to  be  listed  among  the  excretions  of  the  skin. 

Chemical  Composition  of  Sweat. 

Water 995 

Solids: 5 

Organic  acids  (formic,  acetic,  butyric,  propionic, 

caproic,  caprylic) 0.9 

Salts,  chiefly  sodium  chloride 1.8 

Neutral  fats  and  cholesterin 0.7 

Extractives  (including  urea),  with  epithelium 1.6 

1  000 


390  EXCRETION 

The  sweat  is  a  colorless,  slightly  turbid  fluid,  alkaline,  neutral  or  acid  in 
reaction,  of  a  saltish  taste,  and  peculiar  characteristic  odor. 

Of  the  several  substances  it  contains,  however,  only  the  carbonic  acid  and 
water  need  particular  consideration. 

The  quantity  of  watery  vapor  excreted  from  the  skin  is,  on  an  average, 
between  750  and  1,000  cubic  centimeters  daily.  This  subject  has  been  very 
carefully  investigated  by  La  isier  and  Sequin.  The  latter  chemist  enclosed 
his  body  in  an  air-tight  bag  provided  with  a  mouthpiece.  The  bag  was 
closed  by  a  strong  band  above,  and  the  mouthpiece  adjusted  and  gummed 
to  the  skin  around  the  mouth.  He  was  weighed,  then  remained  quiet  for 
several  hours,  after  which  time  he  was  again  weighed.  The  difference  in 
the  two  weights  indicated  the  amount  of  loss  by  pulmonary  exhalation. 
Having  taken  off  the  air-tight  dress,  he  was  immediately  weighed  again,  and 
a  fourth  time  after  a  certain  interval.  The  difference  between  the  two  weights 
last  ascertained  gave  the  amount  of  the  cutaneous  and  pulmonary  exhalation 
together;  by  subtracting  from  this  the  loss  by  pulmonary  exhalation  alone, 
while  he  was  in  the  air-tight  dress,  he  ascertained  the  amount  of  cutaneous 
transpiration.  The  average  loss  by  cutaneous  and  pulmonary  exhalation  in 
a  minute  during  a  state  of  rest  is  eighteen  grains, — the  minimum  eleven  grains, 
the  maximum  thirty-two  grains.  Of  the  eighteen  grains,  eleven  pass  off  by 
the  skin  and  seven  by  the  lungs. 

The  quantity  of  watery  vapor  lost  by  transpiration  is  of  course  influenced 
by  all  external  circumstances  which  affect  the  exhalation  from  evaporating 
surfaces,  such  as  the  temperature,  the  hygrometric  state,  and  the  stillness 
of  the  atmosphere.  But,  of  the  variations  to  which  it  is  subject  under  the 
influence  of  these  conditions,  no  calculation  has  been  exactly  made. 

The  quantity  of  carbonic  acid  exhaled  by  the  skin  on  an  average  is  said  to 
be  about  one-two-hundredth  of  that  eliminated  by  the  pulmonary  respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of  ani- 
mals, more  particularly  the  naked  amphibia,  as  frogs  and  toads,  whose  skin 
is  thin  and  moist,  and  readily  permits  an  interchange  of  gases  between  the 
blood  circulating  in  it,  and  the  surrounding  atmosphere.  Bischoff  found  that, 
after  the  lungs  of  frogs  had  been  tied  and  cut  out,  from  3  to  4  c.c.  of  car- 
bonic-acid gas  was  exhaled  by  the  skin  in  eight  hours.  And  this  quantity 
is  very  large,  when  it  is  remembered  that  a  full-sized  frog  will  generate  only 
about  10  c.c.  of  carbonic  acid  by  his  lungs  and  skin  together  in  six  hours. 

The  importance  of  the  respiratory  function  of  the  skin,  which  was  once 
thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins,  after  re- 
moval of  the  hair,  were  covered  with  an  impermeable  varnish,  has  been  shown 
by  further  observations  to  have  no  foundation  in  fact.  The  immediate  cause 
of  death  in  such  cases  is  the  loss  of  temperature.  A  varnished  animal  is 
said  to  have  suffered  no  harm  when  surrounded  by  cotton  padding,  and  to 
have  died  when  the  padding  was  removed. 


INFLUENCE    OF   THE    NERVOUS    SYSTEM    ON    SWEAT    SECRETION         3P7 

Influence  of  the  Nervous  System  on  Sweat  Secretion.  The  secre- 
tion of  sweat  is  closely  connected  with  the  quantity  of  blood  flowing  through 
the  cutaneous  vessels.  The  quantity  of  sweat  increases  with  vaso-dilatation 
and  diminishes  with  vaso-constriction.  The  sweat  glands  are  also  under  the 
control  of  efferent  impulses  passing  to  them  from  the  special  sweat  centers 
in  the  brain  and  spinal  cord  through  special  sweat  nerves.  Thus,  if  the  sciatic 
nerve  be  divided  in  a  cat  and  the  peripheral  end  be  stimulated,  beads  of  sweat 
are  seen  to  appear  upon  the  pad  of  the  corresponding  foot.  The  sweat  ap- 
pears even  though  at  the  same  time  the  blood-vessels  are  constricted,  or  the 
blood  flow  entirely  stopped  by  compression  of  the  aorta,  whereas  if  atropin  is 
injected  previously  to  the  stimulation,  no  sweat  appears,  although  dilatation  of 
the  vessels  may  be  present.  Secretion  of  sweat,  too,  may  be  brought  about 
reflexlv. 

The  circulation  of  venous  blood  in  the  spinal  bulb  causes  the  sweating  of 
phthisis  and  of  dyspnea  generally,  by  stimulating  the  sweat  center.  If  the 
cat  whose  sciatic  nerve  is  divided  be  rendered  dyspneic,  abundant  sweat 
occurs  upon  the  foot  of  the  uninjured,  and  none  on  the  injured,  side.  The 
effect  of  heat  in  producing  sweating  may  be  both  local  and  general,  and,  again, 
the  various  drugs  which  produce  an  increased  secretion  of  sweat  do  not  all 
act  in  the  same  way;  thus,  there  is  reason  for  thinking  that  pilocarpine  acts 
upon  the  local  apparatus,  that  strychnine  and  picrotoxin  act  upon  the  sweat 
centers,  and  that  nicotine  acts  both  upon  the  central  and  upon  the  local 
apparatus. 

The  special  sweat-nerves  appear  to  issue  from  the  spinal  cord,  in  the 
case  of  the  hind  limb  of  the  cat,  by  the  last  two  or  three  dorsal  and  first 
two  to  four  lumbar  nerves,  pass  to  the  abdominal  sympathetic,  and  from 
thence  to  the  sciatic  nerve,  the  general  course  of  the  autonomic  nerves 
for  this  region.  In  the  case  of  the  fore  limb,  the  nerves  leave  the  cord 
by  the  first  to  the  sixth  dorsal  nerves,  pass  into  the  thoracic  sympathetic, 
and  then  join  the  brachial  plexus,  reaching  the  arm  through  the  median  and 
ulnar  nerves. 

It  will  be  as  well  to  repeat  here  the  other  functions  which  the  skin  sub- 
serves. In  addition  to  its  excretory  office,  we  have  seen  that  it  acts  as  a 
channel  for  absorption.  It  is  also  concerned  with  the  special  senses,  that  of 
touch  and  temperature,  to  the  consideration  of  which  as  well  as  to  its  function 
of  regulating  the  temperature  of  the  body  we  shall  presently  return.  By  its 
general  impermeability  it  prevents  the  loss  of  moisture  of  the  body  by  direct 
evaporation  from  the  tissues.  It  should  be  recollected,  however,  that  apart 
from  these  special  functions,  by  means  of  its  toughness,  flexibility,  and  elastic- 
ity, the  skin  is  eminently  qualified  to  serve  as  the  general  integument  of  the 
body,  for  defending  the  internal  parts  from  external  violence,  while  readily 
yielding  and  adapting  itself  to  their  various  movements  and  changes  of 
position. 


398  EXCRETION 

LABORATORY   EXPERIMENTS    IN    EXCRETION. 
PHYSIOLOGICAL  REACTIONS 

i.  The  Relation  of  Blood  Flow  through  the  Kidney  to  the  Secre- 
tion of  Urine.  Properly  to  check  this  experiment  one  should  make 
three  determinations:  i,  the  general  blood  pressure;  2,  the  volume  of  the 
kidney;  3,  the  amount  of  urine  secreted.  Anesthetize  a  dog  and  arrange  the 
apparatus  for  taking  the  blood  pressure  as  directed  in  experiment  19.  Prepare 
a  renal  onkometer,  see  figures  301  and  302,  and  an  onkograph  for  recording 
the  variations  in  the  volume  of  the  kidney.  The  renal  onkometer  consists  of 
a  double  metal  box  to  fit  the  form  of  a  kidney.  The  inner  halves  of  this  box 
should  be  covered  so  loosely  with  very  thin  sheet  rubber  that  the  rubber  can 
be  fitted  into  the  bottom  of  the  cup  without  undue  tension.  The  rubber  must 
be  sealed  to  the  outer  edges  of  this  inner  cup  with  rubber  cement  and  allowed 
to  dry.  When  it  is  completely  dried  the  inner  cup  should  be  adjusted  to  the 
outer,  and  the  spaces  enclosed  by  the  rubber  sheet  filled  with  water.  Or 
the  onkometer  may  be  closed  with  parchment  and  filled  with  oil  as  de- 
scribed in  experiment  23  on  the  Circulation.  The  half  of  the  onkometer 
that  comes  against  the  wall  of  the  body  cavity  of  the  animal  should  be 
completely  closed  with  a  stopper  before  the  instrument  is  adjusted  to 
the  kidney.  Now  adjust  the  onkometer  to  the  kidney,  taking  care  to 
place  the  renal  arteries,  veins,  and  ureter  in  the  tube  in  such  a  way  as  not 
to  compress  them.  Fill  the  outer  cup  with  water  and  connect  this  cavity 
by  a  two-way  cannula  with  the  recording  onkograph.  In  practice  it  is  more 
satisfactory  if  one  introduces  between  the  onkometer  and  onkograph  an  over- 
flow bottle  or  bulb,  adjusted  to  maintain  the  constant  pressure  on  the  kidney. 
This  direction  varies  from  the  usual  one  in  that  rubber  sheeting  instead  of 
parchment  is  used  to  cover  the  inner  cup  of  the  onkometer,  a  method  that 
permits  the  use  of  water  instead  of  oil. 

Isolate  and  insert  a  small  cannula  into  the  ureter.  This  cannula  should 
be  clamped  in  a  stand  at  a  level  as  little  above  that  of  the  kidney  as  possible. 
The  urine  secreted  may  be  collected  in  a  10  c.c.  graduated  cylinder  and 
measured  at  intervals  of  5  or  10  minutes.  Or,  if  the  outflow  is  scanty,  it  may 
be  allowed  to  drop  on  a  tambour  recording  apparatus,  the  rate  of  dropping 
being  indicative  of  the  rapidity  of  secretion. 

Determine  the  normal  rate  of  secretion  of  a  dog  under  constant  anesthesia. 
The  anesthesia  should  be  medium  to  light,  but  should  be  kept  very  uni- 
form so  as  to  maintain  a  strong  blood  pressure.  Note  the  effect  on  secre- 
tion and  the  corresponding  effect  on  blood  pressure  and  the  kidney  volume 
produced  by  vagus  inhibitions.  Section  the  vagus  nerves  and  produce  in- 
hibition by  stimulating  the  peripheral  end  of  the  vagus.  In  this  instance 
there  are  no  reflexes  to  complicate  the  experiment,  so  that  the  fall  in  blood 


SECRETORY    NERVES    FOR   THE    SWEAT    GLANDS  399 

pressure  is  a  direct  cardiac  effect.  Stimulate  the  central  end  of  the  vagus 
which  produces  a  fall  of  blood  pressure  through  the  vaso-motor  system. 
There  should  be  a  normal  period  of  at  least  ten  minutes  following  each  experi- 
ment to  allow  the  secretion  of  the  kidney  to  return  to  the  normal. 

Expose  the  splanchnic  nerves  at  the  point  where  they  pass  beneath  the 
diaphragm  into  the  abdominal  cavity.  Adjust  a  pair  of  shielded  electrodes, 
close  the  cavity,  and,  when  the  animal  has  returned  to  the  normal  uniform 
rate  of  secretion  and  of  blood  pressure,  stimulate  the  splanchnic  nerves. 
The  splanchnics  contain  vaso-constrictor  nerves  for  the  kidney.  The  onkom- 
eter  experiment  should,  therefore,  demonstrate  a  sharp  decrease  in  the  vol- 
ume of  the  organ,  while  the  blood  pressure  is  only  slightly  changed.  The 
rate  of  secretion  should  be  followed  for  at  least  twenty  minutes  after  stimula- 
tion of  the  splanchnics.     This  test  should  be  repeated  two  or  three  times. 

In  this  connection  demonstrate  the  influence  of  deep  chloroform  anesthesia 
on  urinary  secretion.  The  chloroform  should  be  pushed  to  the  danger  limit 
and  maintained  there  for  a  couple  of  minutes  or  more.  Compare  the  rapidity 
of  the  recovery  of  blood  pressure  with  the  recovery  of  the  rate  of  secretion. 

2.  Secretory  Nerves  for  the  Sweat  Glands.  Langley  has  mapped 
out  the  paths  of  the  secretory  nerves  for  the  sweat  glands.  He  has  shown 
that  in  the  cat  these  fibers  are  distributed  to  the  hind  limb  through  the  sciatic. 
Anesthetize  a  half -grown  cat,  isolate  the  sciatic  nerve,  cut  it  and  stimulate  the 
peripheral  end  with  a  medium  to  strong  induction  current.  After  a  few 
moments  beads  of  perspiration  will  appear  on  the  pads  of  the  foot,  which 
should  therefore  be  carefully  examined  before  the  experiment. 

URINE  ANALYSIS. 

3.  Daily  Quantity.  Determine  the  total  quantity,  for  24  hours, 
of  urine  secreted  through  a  period  of  3  or  4  days,  beginning  and  ending  the 
period  at  a  definite  hour  in  the  day,  preferably  on  rising  in  the  morning. 
The  daily  secretion  varies  through  wide  extremes,  depending  upon  the  quan- 
tity of  liquid  taken  in  the  food,  the  daily  exercise,  the  temperature,  etc.,  etc. 
In  the  analysis  of  urine  it  is  always  better  to  take  a  mixed  24-hour  sample. 

4.  Specific  Gravity.  Determine  the  specific  gravity  of  24-hour 
urine.  This  is  done  by  the  instrument  known  as  the  urinometer  which 
carries  a  graduated  scale  at  the  neck.  Care  should  be  taken  to  float  the 
urinometer  so  that  it  does  not  come  in  contact  with  the  measuring  cylinder. 
The  scale  should  be  read  at  the  bottom  of  the  meniscus. 

5.  Reaction.  Determine  the  reaction  of  perfectly  fresh  urine,  using 
litmus  paper.  The  normal  urine  is  slightly  acid  under  ordinary  conditions, 
due  to  the  presence  of  acid  phosphates  or  perhaps  in  some  cases  to  traces  of 
free  organic  acid. 

After  standing  some  time  the  reaction  is  usually  alkaline,  owing  to  fer- 


400 


EXCRETION 


mentation  processes.  The  reaction  may  vary  also  according  to  the  food, 
vegetable  foods  tending  to  produce  alkaline  urine,  while  with  animal  foods 
the  reaction  is  acid. 

6.  The   Total  Quantity  of   Solids.      Determine  the  solids  of   urine 

by  evaporating  25  c.c.  of  a  mixed  sample  of  urine  to  dryness  in  a  weighed 

platinum  or  porcelain  dish   over   a   water   bath.     The 

residue  should  be  dried  to  constant  weight  in  a  drying 

oven  at  1050  C. 

A  useful  rule  for  approximately  estimating  the  total 
solids  in  any  given  specimen  of  healthy  urine  is  to 
multiply  the  last  two  figures  representing  the  specific 
gravity  by  2.33.  Thus,  in  urine  of  specific  gravity  1025, 
2.33  X  25  =  58.25  grains  of  solids  are  contained  in 
1,000  grains  of  the  urine.  Or  the  total  solids  are  5.825 
per  cent.  In  using  this  method  it  must  be  remembered 
that  the  limits  of  error  are  much  wider  in  diseased  than 
in  healthy  urine. 

The  solids  of  urine  consist  of  inorganic  salts  of 
sodium,  potassium,  and  calcium,  and  of  a  long  list  of 
organic  compounds,  chiefly  nitrogenous. 

7.  Chlorides.  Large  quantities  of  sodium  chlo- 
ride are  always  present  in  the  normal  urine.  Add 
ammonia  to  25  or  50  c.c.  of  albumin-free  urine  and  heat 
to  precipitate  earthy  phosphates,  filter.  To  a  sample 
of  the  filtrate  add  an  excess  of  strong  nitric  acid  and  a 
few  drops  of  1  per  cent  silver  nitrate.  A  white  flocculent  precipitate  of 
silver  chloride  comes  down.  This  precipitate  is  soluble  in  an  excess  of 
ammonia.  Reprecipitate  by  adding  nitric  acid  again.  The  test  may  be 
made  without  removing  the  phosphates,  though  in  this  case,  upon  adding 
ammonia,  the  disappearance  of  the  silver  precipitate  is  complicated  by  the 
appearance  of  insoluble  phosphates. 

The  chlorides  may  be  estimated  quantitatively  by  Volhard's  method,  or 
some  one  of  its  modifications,  which  depends  upon  the  determination  of  the 
amount  of  chlorine  precipitated  by  the  silver.  The  student  is  referred  to 
chemical  text-books  for  this  and  other  quantitative  methods. 

8.  Sulphates.  Sulphates  exist  in  the  urine  both  in  inorganic 
and  organic  compounds,  chiefly  the  former.  Add  a  few  drops  of  hydro- 
chloric acid  to  a  sample  of  urine  in  a  test  tube,  then  a  solution  of  barium 
chloride,  the  insoluble  barium  sulphate  settles  out.  If  the  test  is  made  on  the 
normal  urine  without  the  addition  of  the  acid,  the  inorganic  sulphate  will  be 
precipitated,  while  the  ethereal  or  compound  sulphate  will  remain  in  solution 
and  can  be  filtered  off.  This  filtrate,  when  boiled  with  strong  hydrochloric 
acid  to  10  per  cent  over  a  water  bath  for  a  short  time,  will  have  the  sulphates 


Fig.  308.— The 
Urinometer. 


PHOSPHATES 


401 


split  off  from  the  organic  radicle  and  may  be  precipitated  by  the  addition 
of  barium  chloride  in  hot  solution. 

9.  Phosphates.  The  phosphates  of  urine  consist  of  the  earthy 
and  alkaline  salts,  the  latter  predominating.  Take  a  50  c.c.  sample  of  urine, 
add  strong  ammonia,  and  heat.  The  phosphates  of  calcium  and  magnesium 
separate  out,  as  they  are  insoluble  in  aikaline  solution.     Filter. 

To  the  filtrate  add  a  solution  of  magnesium  sulphate.  This  precipitates 
the  sodium  and  potassium  phosphates  as  a  triple  phosphate  of  magnesium, 
which  is  insoluble.     Tests  for  phosphates  in  general  are: 

Add  nitric  acid  to  a  sample  of  urine,  warm  gently,  then  add  a  few  drops 
of  10  per  cent  ammonium  molybdate;  a  yellow  precipitate  of  ammonium 
phospho-molybdate  is  formed.     Or,  add  acetic  acid,  then  a  few  drops  of 


Fig.  309. — Doremus'  Ureometer. 


uranium  acetate;  a  bright  yellow  precipitate  of  uranium  ammonium  phosphate 
is  formed.  These  two  reactions  are  used  as  the  basis  for  a  quantitative  de- 
termination of  phosphorus. 

10.  The  Preparation  of  Urea.  Take  100  c.c.  of  normal  urine,  evap- 
orate to  one-half  its  quantity,  and  precipitate  the  phosphates  and  sulphates 
by  adding  a  mixed  solution  of  barium  hydrate  and  nitrate.  Filter,  evaporate 
the  filtrate  to  dryness,  take  up  in  warm  95  per  cent  alcohol,  and  refilter.  Crys- 
tals of  urea  separate  out  when  the  alcohol  is  evaporated  off. 

Evaporate  a  large  sample,  200  c.c,  of  urine  to  a  syrupy  mass,  add  nitric 
acid.  Crystals  of  urea  nitrate  are  formed.  Wash  the  crystals  in  dilute  nitric 
acid,  then  dissolve  in  water.  The  urea  is  set  free  by  adding  barium  carbonate 
26 


402  EXCRETION 

until  the  carbon  dioxide  ceases  to  come  off.  Filter,  evaporate  over  a  water 
bath  to  dryness,  and  dissolve  the  urea  in  95  per  cent  alcohol;  decant,  and  re- 
crystallize  by  evaporating  off  the  alcohol. 

11.  Urea  Determination  by  Doremus'  Ureometer.  Fill  the  ureo- 
meter  with  hypobromite  of  sodium  solution.  Take  a  sample  of  urine  in 
the  pipet  which  accompanies  the  instrument,  drawing  it  in  exactly  to  the 
mark.  Insert  the  pipet  past  the  bend  of  the  ureometer  and  slowly  empty 
the  urine  carefully  so  as  not  to  lose  any  of  the  liberated  nitrogen.  The  instru- 
ment is  graduated  to  read  off  the  percentage  of  urea  directly. 

12.  Uric  Acid.  Concentrate  over  a  water  bath  500  c.c.  of  urine 
to  100  c.c.  and  boil  with  10  c.c.  or  more  of  strong  hydrochloric  acid.  Upon 
cooling,  crystals  of  uric  acid  are  formed.  Decant  the  supernatant  liquid  and 
wash  the  crystals  with  a  few  cubic  centimeters  of  10  per  cent  hydrochloric 
acid.     Dissolve  the  crystals  and  test. 

The  Murexide  Test.  Add  to  2  c.c.  of  uric  acid  solution  in  a  test  tube  an 
equal  quantity  of  nitric  acid.  Heat  gently,  a  reddish  ring  forms  at  the  point 
of  contact  between  the  nitric  acid  and  uric  acid  solution.  Cool  and  add 
ammonia  carefully.  The  color  ring  deepens  to  a  purple  color.  This  test 
succeeds  well  by  evaporating  a  few  drops  of  uric  acid  on  a  porcelain  plate. 
Add  to  the  stain  a  drop  of  concentrated  nitric  acid  and  evaporate.  Concen- 
tric rings  of  reddish  color  will  be  formed.  This  color  deepens  to  reddish- 
purple  when  a  drop  of  ammonia  is  added. 

13.  Creatinin.  Test  20  c.c.  of  urine  in  a  beaker  for  creatinin  by 
adding  a  cubic  centimeter  of  dilute  solution  of  sodium  nitroprusside  and  then 
weak  sodium  hydrate.  A  ruby-red  color,  which  quickly  turns  yellow,  indi- 
cates the  presence  of  creatinin.  (Weyl's  reaction.)  If  the  yellow  solution 
has  an  excess  of  acetic  acid  added  and  is  then  boiled,  it  turns  first  green  and 
later  blue,  forming  ultimately  a  precipitate  of  Prussian  blue. 

Urine  mixed  with  picric  acid  gives  a  red  coloration  when  made  alkaline 
with  caustic  alkali  solution. 

14.  Total  Nitrogen  in  Urine.  Determine  the  total  nitrogen  in 
a  sample  of  urine  by  the  Kjeldahl  method.  This  method  depends  upon  the 
conversion  of  -ill  the  nitrogen  to  ammonia,  the  distillation  of  this  ammonia 
into  a  known  quantity  of  sulphuric  acid,  and  the  final  titration  of  the  excess 
of  sulphuric  acid  when  the  distillation  is  complete.  The  computation  is 
made  on  the  basis  that  1  c.c.  of  a  normal  sulphuric  acid  is  equivalent  to 
1  c.c.  normal  sodium  hydrate,  and  that  in  turn  to  1  c.c.  of  ammonium 
hydrate.  The  ammonia  neutralizes  a  portion  of  the  sulphuric  acid  in  the 
distillation.  One  c.c.  of  normal  ammonium  hydrate  contains  0.014  gram 
nitrogen,  from  which  the  total  nitrogen  in  the  sample  used  can  be  readily 
computed. 

15.  Pigments  of  Urine.  The  normal  color  of  the  urine  is  due  to 
the  presence  of  a  pigment,  urobilin.     Prepare  urobilin  by  adding  lead  acetate 


ALBUMIN    IX    THE    URINE  403 

to  a  200  c.c.  sample  of  urine.  A  precipitate  forms  which  carries  down  the 
coloring  matter.  Filter.  Add  acid  alcohol  to  the  precipitate  to  extract  the 
coloring  matter,  refdter,  which  gives  a  deep  yellow  solution.  Shake  up  with 
a  few  cubic  centimeters  of  chloroform  which  dissolves  the  pigment.  Draw 
off  the  chloroform  solution  and  allow  to  evaporate.  The  residue  is  a  brown- 
ish mass  of  urobilin. 

ABNORMAL  CONSTITUENTS  OF  URINE. 

Many  abnormal  constituents  may  appear  in  the  urine  under  pathological 
conditions,  only  two  of  which  will  be  mentioned  here. 

16.  Albumin  in  the  Urine.  The  detection  of  the  presence  of  albu- 
min, albuminuria,  is  of  considerable  clinical  importance.  The  following 
are  the  standard  tests  which  present  no  special  difficulty  except  when  traces 
only  are  present. 

Heat  Coagulation.  To  a  half  test  tube  of  urine  add  a  drop  of  dilute 
acetic  acid  and  boil.  A  white  coagulum  indicates  the  presence  of  albumin. 
A  faint  cloudy  appearance  indicates  traces. 

Nitric  Acid  Test.  To  5  c.c.  of  strong  nitric  acid  in  a  conical  test  tube 
add  10  or  15  c.c.  of  urine,  pouring  it  gently  down  the  inclined  side  of  the  glass. 
Allow  the  gl-iss  to  stand  for  a  few  minutes,  when  a  white  coagulum  appears 
just  above  the  line  of  contact  of  the  acid  with  the  urine.  This  test,  known 
as  Heller's  test,  will  usually  indicate  the  presence  of  traces  of  albumin. 

Picric  Acid  Test.  Add  picric  acid  to  a  sample  of  urine.  A  whitish 
precipitate  of  albumin  will  appear  at  the  line  of  contact,  as  in  the  preceding  test. 

Citric  acid  two  parts  and  picric  acid  one  part,  when  boiled  with  urine 
will  coagulate  minute  traces  of  the  proteid. 

17.  Detection  of  Sugar  in  the  Urine.  Trommers  Test.  The 
presence  of  sugar  in  the  urine  can  usually  be  detected  by  Trommer's  test, 
which  depends  upon  the  reduction  of  copper  sulphate  in  the  presence  of 
strong  alkali.  Boil  fresh  Fehling's  solution  and  add  to  it  a  few  cubic  centi- 
meters of  urine.  When  sugar  is  present  a  reddish-yellow  precipitate  of  copper 
oxide  comes  out.  The  test  should  be  set  away  for  a  few  minutes  when,  if 
only  traces  of  the  reduction  are  present,  a  reddish-brown  stain  will  appear 
on  the  bottom  of  the  test  tube.  Uric  acid,  if  present  in  excess,  may  produce 
a  slight  precipitation  of  the  copper. 

Fermentation  Test.  If  sugars  are  present  in  the  urine,  they  can  be  de- 
tected by  adding  yeast  to  a  fermentation  tube  filled  with  urine,  the  liberation 
of  carbon  dioxide  indicating  the  presence  of  sugar.  Cane  sugar  does  not 
support  the  growth  of  yeast,  so  it  forms  an  exception  by  this  test. 

Phenyl-Hydrazin  Crystals.  Phenyl-hydrazin  forms  crystals  of  phenyl- 
glucosazone.  To  10  c.c.  of  urine  in  a  small  beaker  add  0.1  of  a  gram  of 
phenyl-hydrazin   hydrochloride  and  a  double   quantity  of  sodium   acetate. 


404  EXCRETION 

Heat  in  the  water  bath  for  20  minutes.  Upon  cooling  a  deposit  of  yellow 
crystals  of  phenyl-glucosazone  takes  place,  if  glucose  is  present. 

18.  Quantitative  Determination  of  Sugar  in  the  Urine.  Fill  a  10- 
c.c.  graduated  pipet  with  freshly  prepared  Fehling's  solution.  Take  10  c.c. 
of  urine,  measured  with  a  dropping-pipet  into  a  small  beaker,  and  boil.  While 
continuing  to  boil,  add  Fehling's  solution  slowly  and  cautiously  so  long  as 
the  color  is  discharged.  The  amount  of  Fehling's  required  to  reduce  the  sugar 
is  a  measure  of  the  quantity  of  reducing  sugar  present — 1  c.c.  of  Fehling's 
being  equivalent  to  5  milligrams  of  dextrose. 

For  the  presence  of  blood  pigments  and  other  abnormal  constituents  of 
the  urine,  the  student  is  referred  to  special  handbooks  on  the  subject. 


CHAPTER  XI 

METABOLISM,    NUTRITION,   AND    DIET 

The  term  metabolism  means,  literally,  an  exchange  of  material.  In  its 
broadest  physiological  sense  it  includes  the  study  of  the  exchange  of  material 
between  the  living  tissues  of  the  body  and  their  surrounding  media.  This 
includes  the  study  of  the  income  and  outgo  of  material;  the  storing  of  energy- 
yielding  materials  in  the  body;  the  transfer  of  this  potential  energy  into  kinetic 
energy;  and  the  nutritional  processes  within  the  various  tissues.  The  building 
up  of  absorbed  food  material  into  the  protoplasm  of  the  cell  or  of  simpler  com- 
pounds into  more  complex  ones,  which  may  be  stored  in  the  cell,  is  known 
as  anabolism,  and  the  compounds  themselves  as  anabolites.  The  breaking 
down  of  these  substances  into  simpler  forms,  whereby  the  potential  energy 
of  the  anabolites  is  transformed  into  kinetic  energy,  is  known  as  calabolism, 
and  its  products  as  catabolites. 

In  order  to  form  an  estimate  of  these  processes  going  on  in  the  body,  the 
amount  and  nature  of  the  ingested  material  must  be  known,  as  well  as  the 
amount  of  refuse  or  unused  material  that  passes  out  of  the  alimentary  canal 
as  feces,  and  the  amount  of  excreted  material  from  the  various  excretory 
organs.  It  is  also  necessary  to  know  the  potential  energy  of  the  ingested 
materials,  and  the  possible  potential  energy  must  be  checked  against  the  ac- 
tual energy  liberated. 

The  food  is  intended  to  supply  the  place  of  the  material  which  has  been 
utilized  by  the  body,  and,  in  a  simpler  form,  eliminated  in  the  excretions. 
But  in  the  choice  of  a  diet  this  is  not  enough;  the  food  should  be  sufficient 
to  supply  such  need  without  waste  and  without  unduly  increasing  the  output 
of  excreta,  while  at  the  same  time  the  body  should  be  maintained  in  health, 
without  increase  or  loss  of  weight.  The  food  must  also  supply  the  energy 
liberated  without  undue  waste  of  the  tissues  themselves. 

These  requisites  of  a  diet  scale  then  allow  for  wide  alterations  in  the 
amount  of  different  kinds  of  foods  under  different  circumstances.  Numerous 
and  most  valuable  experiments  have  been  performed  in  recent  years  to  determine 
just  what  each  article  of  the  common  food  materials  contributes  to  the  growth 
of  the  tissues  and  to  the  kinetic  energy  liberated  by  the  tissues.  The  potential 
energy  of  the  food  can  also  be  checked  against  the  kinetic  energy  liberated. 
A  single  illustration  of  this  class  will  serve.  In  an  experiment  with  mixed  food 
lasting  through  four  days,  on  a  man  with  body  weight  of  64  kilograms,  and 
doing  a  minimum  amount  of  work,  Atwater  made  the  following  determinations: 

405 


406 


METABOLISM,    NUTRITION,    AND    DIET 


Weight,  Composition,  and  Heat  of  Combustion  of  Foods  and  Excreta  per  Day. 


to  J 
'5 

u 

d 
'8 
0 

u 

a, 

fn 

O  ci 

-     X)  v. 

0) 
O 

a 

0 

M 
0 
u 

s 

0 

a 

V 
M 
O 
u 
•V 
>. 

B 

E 

0  • 

0  G 
O'V 

~  3 
rt  n 
0)-" 

Food 
Beef 

Grams. 

IOO 

25 
85o 
300 

5° 
5° 
20 

Grams. 

61.2 

2.6 

726.8 
123.9 

4-1 
3-3 

Grams. 

35-i 

•  5 

32-3 

22.2 

4-8 
2.8 

Grams. 

3-i 
21 . 1 

45- 1 
12.0 

-7 
3-6 

Grams. 

39-9 
139.2 

39-7 
39-2 
20.0 

Grams. 
5.62 
.08 
5.10 
3-00 

.84 

-5° 

Grams. 

20.05 

15-77 
67.74 

82.53 

20.46 

21.12 
8.42 

Grams. 
2.90 
2.50 

9-94 
12.24 

2.87 

3-07 
1.30 

Calo- 
ries. 
227 
194 
768 
835 

204 

212 

79 

Butter 

Whole  milk 

Bread 

Shredded  wheat 

biscuit 

Ginger  snaps 

Sugar 

Total    food    per 

1,395 

921.9    97.7 

85.6 

278.0 

16.04 

236.09 

34.82 

2,519 

Average        feces 
per  day 

Average       urine 
per  day 

Excretions  lungs 
and  skins . 

98.8 
1420. 8 

77-7 
1363-9 

881.0 

7-7 

4.0 

6-3 

1.23 

15 -»5 

9-98 
1 1 .  79 
221.5 

1 .42 

2.  98 

no 

135 

2397 

Total        excreta 
per  day 

2322.6 

.... 

17.08      243.27 

4.4O 

2642 

.... 

—  1.04 

-7.18 

+  3°-42 

-123 

Careful  analyses  of  the  excreta,  many  of  which  we  have  already  had  oc- 
casion to  call  attention  to,  show  that  they  are  made  up,  besides  water,  chiefly 
of  the  chemical  elements  carbon,  hydrogen,  oxygen,  and  nitrogen,  but  that 
they  also  contain,  to  a  less  extent,  sulphur,  phosphorus,  chlorine,  potassium, 
sodium,  calcium,  magnesium,  iron,  and  certain  other  of  the  elements.  Since 
this  is  the  case  it  must  be  evident  that,  to  balance  this  waste,  foods  must  be 
supplied  containing  all  these  elements  to  a  certain  degree,  and  some  of 
them  in  large  amount,  viz.,  those  which  take  a  principal  part  in  forming 
the  excreta. 

The  waste  products  of  the  body  are  eliminated  through  the  lungs,  the 
skin,  the  alimentary  canal,  and  the  kidney.  In  the  lungs  the  chief  waste  prod- 
uct is  water,  carbonic-acid  gas,  and  traces  of  ammonia  compounds  which 
are  composed  of  the  elements  carbon,  oxygen,  nitrogen,  and  hydrogen.  Traces 
of  carbonic-acid  gas  and  small  quantities  of  urea  and  salts  are  eliminated 
through  the  skin.  From  the  alimentary  canal  there  are  lost,  through  the  feces, 
the  indigestible  and  unabsorbed  substances  from  the  food,  together  with 
products  secreted  into  the  canal  by  the  liver,  pancreas,  and  mucous  membrane. 


METABOLISM,    NUTRITION,    AND    DIET 


407 


The  secretion  lost  daily  by  the  kidney,  aside  from  a  large  quantity  of  water, 
consists  of  nitrogenous  waste  products,  chiefly  urea,  and  inorganic  solids,  as 
were  mentioned  in  the  chapter  on  Excretion. 

The  relations  between  the  amounts  of  the  chief  elements  contained  in  these 
various  excreta  in  twenty-four  hours  may  be  thus  summarized- 


Water. 

C. 

H. 

N. 

O. 

By  the  lungs 

By  the  skin 

33° 

660 

1,708 

120 

248.8 
2.6 
9.8 
20. 

3-3 
3-o 

15-8 
3-o 

65!-i5 

7-2 

By  the  urine 

By  the  feces 

Grams 

2,818 

281.2 

6-3 

18.8 

681.45 

From  the  water  in  this  table  should  be  subtracted  the  296  grams  of  water 
which  are  produced  by  the  union  of  hydrogen  and  oxygen  in  the  body  during 
the  process  of  oxidation,  and  there  should  be  added  to  the  respective  columns 
the  corresponding  amounts  of  the  constituent  elements,  i.e.,  33  grams  of  hydro- 
gen and  262  grams  of  oxygen.  There  are  26  grams  of  salts  eliminated  through 
the  urine,  and  6  by  the  feces;   a  total  of  32  grams. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to  about  281.2 
grams  and  of  nitrogen  18.8  grams,  and  if  a  man  could  be  fed  by  these  elements, 
as  such,  the  problem  would  be  a  very  simple  one;  a  corresponding  weight 
of  charcoal  and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air  would  be 
all  that  is  necessary.  But  an  animal  can  live  upon  these  elements  only  when 
they  are  arranged  in  a  particular  manner  with  others,  in  the  form  of  such 
food  stuffs  as  we  have  already  enumerated,  page  297  el  seq.;  moreover,  the 
relative  proportion  of  carbon  to  nitrogen  in  either  of  these  compounds  alone 
is  by  no  means  the  proportion  required  in  the  diet  of  man.  Thus,  in  proreid, 
the  proportion  of  carbon  to  nitrogen  is  only  as  3.5  to  1.  If,  therefore,  a  man 
took  into  his  body,  as  food,  sufficient  proteid  to  supply  him  with  the  needed 
amount  of  carbon,  he  would  receive  more  than  four  times  as  much  nitrogen 
as  is  needed;  and  if  he  took  only  sufficient  to  supply  him  with  nitrogen,  he 
would  be  starved  for  want  of  carbon.  It  is  plain,  therefore,  that  he  should 
take  with  the  albuminous  part  of  his  food,  which  contains  so  large  an  amount 
of  nitrogen  in  proportion  to  the  carbon  he  needs,  substances  in  which  the 
nitrogen  exists  in  relatively  much  smaller  quantities  than  the  carbon. 

It  is,  therefore,  evident  that  the  diet  must  consist  of  several  compounds, 
not  of  one  alone. 

Many  valuable  observations  have  been  made  with  a  view  of  ascertaining 
the  effect  upon  the  metabolism  of  a  variation  in  the  amount  and  nature  of 
food.    These  are  of  great  assistance  in  the  consideration  of  dietetics. 


408 


METABOLISM,    NUTRITION,    AND    DIET 


METABOLISM  OF  PROTEIDS. 

Nitrogenous  Equilibrium.  Experiments  have  been  made,  to  a  con- 
siderable extent  upon  dogs,  which  demonstrate  the  necessity  for  proteid 
food.  After  a  preliminary  period  without  food,  during  which  the  output  of 
nitrogen  as  shown  by  the  urea  has  diminished  to  a  comparatively  constant 
amount,  an  animal  is  fed  with  a  diet  of  lean  meat  which  would  suffice  to  pro- 
duce the  amount  of  urea,  and  so  of  flesh,  which  it  has  been  losing  during  its 
starvation  period.  The  effect  of  this,  however,  is  at  once  to  send  up  the 
amount  of  urea  excreted  to  a  point  above  that  which  had  been  lost  previous 
to  the  commencement  of  the  flesh  diet.  Thus  the  output  of  nitrogen  still 
exceeds  its  income,  and  the  weight  of  the  animal  continues  slowly  to  diminish. 
It  is  only  after  a  considerable  increase  of  the  flesh  given  in  the  food  that  a 
point  is  reached  where  the  income  and  expenditure  of  nitrogen  are  equal, 
and  at  which  the  animal  is  not  using  up  quickly  or  slowly  the  nitrogen  of  its 
own  tissue,  and  is  no  longer  losing  flesh.  This  condition  in  which  the  nitro- 
gen of  the  egesta  equals  the  nitrogen  of  the  ingesta  is  known  as  nitrog- 
enous equilibrium. 

Experiment    in    Nitrogenous    Equilibrium. 


Days  of   Experiment. 


I.    i-5- 
6-12 

II.     1-2.. 

III.    1-7. . 
8-17 


N 
Intake. 
Grams. 


90.00 
131.60 

35-8o 

144-5° 
154.81 
213.72 


N 
Output. 
Grams. 


89.81 

I32-75 
36.16 

!43-!3 
153.02 
213.26 


JPer  cent 
Differ- 
ence. 


-fo.88 
-|-i  -OO 
—0.86 
—O.51 


S 

Intake. 
Grams. 


•77 


s 

Output. 
Grams. 


I  2  .  79 


In  the  dog,  according  to  Waller,  nitrogenous  equilibrium  does  not  occur 
until  the  amount  of  flesh  of  the  food  is  over  three  times  as  great  as  would  be 
necessary  to  supply  the  nitrogen  of  the  urea  during  a  period  of  starvation. 
Thus  a  dog  excretes  during  a  starvation  period  0.5  gram  of  urea  per  kilo 
of  body  weight;  in  order  to  satisfy  this  waste  it  would  be  necessary  to  ad- 
minister 1.5  grams  per  kilo  of  meat;  this  at  once  increases  the  urea  excreted 
to  about  0.75  gram  per  kilo  of  body  weight,  and  nitrogenous  equilibrium 
is  not  attained  until  over  three  times,  viz.,  3  grams  per  kilo  of  body  weight, 
of  meat  is  given.  Foster  gives  even  a  larger  figure.  The  effect,  therefore, 
of  proteid  food  is  largely  to  increase  the  excretion  of  urea,  which  indicates 
an  increase  in  the  metabolism  of  the  tissues. 

Studies  in  nitrogenous  equilibrium  are   based  on  the  fact  that  when  an 


THE    ROLE    OF    PROTEIDS    IN    METABOLISM  409 

animal  is  given  a  diet  with  a  constantly  increasing  amount  of  proteid  food 
from  day  to  day,  after  a  few  days  the  total  nitrogen  found  in  the  excreta 
exactly  balances  that  taken  in  the  food.  This  condition  of  nitrogenous 
equilibrium  is  established  at  different  levels,  varying  sometimes  according  to 
the  individual  and  with  the  kind  and  quantity  of  other  food  principles  taken 
at  the  same  time  as  the  nitrogenous  foods. 

Chittenden's  latest  metabolism  experiments  have  shown  that  with  free 
choice,  but  moderate  use,  of  accessory  articles  of  diet,  the  human  body  can 
maintain  itself  in  nitrogenous  equilibrium  for  at  least  several  months  on  an 
average  of  4  to  10  grams  of  nitrogen  per  day,  the  equivalent  of  25  to  62.5 
grams  of  proteid. 

The  Role  of  Proteids  in  Metabolism.  The  proteids  of  food  are 
described  by  Voit  as  having  two  relations  to  the  proteid  metabolism  and  to 
outgoing  urea;  the  first  part  going  to  maintain  the  ordinary  and  quiet  metab- 
olism of  the  tissues,  for  which  purpose  it  is  actually  built  up  into  the  living 
protoplasmic  molecule,  and  the  second  part  causing  a  more  rapid  formation 
of  urea,  but  never  becoming  a  part  of  the  actual  protoplasmic  molecule.  The 
former  proteids  are  called  morpJwtic  or  tissue  proteids,  the  latter  circulating 
or  floating  proteids.  Normally  more  proteid  is  eaten  than  is  needed  to  sup- 
ply proteid  to  the  protoplasm  for  growth,  as  has  just  been  stated.  Pfliiger 
takes  the  view,  however,  that  the  tissues  must  have  an  excess  of  proteid  to 
destroy  in  order  to  perform  their  metabolic  processes  normally.  This  use 
of  the  proteids  to  form  heat  by  their  oxidation,  and  not  to  produce  tissue,  was 
looked  upon  by  the  older  physiologists  as  a  wasteful  use  of  good  material, 
and  was  called  a  litxus  consumption. 

Folin  has  recently  announced  a  theory  of  proteid  metabolism  in  which 
he  calls  special  attention  to  the  relation  of  the  nitrogenous  excretion  products 
to  the  nitrogenous  intake.  He  has  shown  that  the  urea  contained  in  the 
urine  varies  almost  directly  with  the  quantity  of  proteid  in  the  food;  that 
the  ammonia  varies  with  the  proteid  in  the  food;  that  the  uric  acid  decreases 
(and  increases)  with  the  proteid  in  the  food,  but  not  in  direct  ratio;  while  the 
creatinin  excreted  is  "  wholly  independent  of  quantitative  changes  in  the  total 
amount  of  nitrogen  eliminated." 


Table  Showing  the  Output   of   Nitrogen   in   a  Normal,  Healthy    Individual 

on  a  Food  Rich   in  Nitrogen,  July    13TH,  and  Poor  in  Nitrogen 

July    20TH  (Folin). 

July   13th.  July  20th. 

Volume  of  urine 1,170   r.c.  385  c.c. 

Total  nitrogen 16.08  grams  3 -60  grams 

Urea-nitrogen 14-70     "     =  87.5  per  cent  22.0      "      =  61.7  per  cent 

Ammonia-nitrogen....  0.49      "     =     3.0  "  0.42     "      =11.3       " 

Uric-acid-nitrogen  ....     0.18     "     =      1.1  "  0.09     "      =     2.5       " 

Kreatinin-nitrogen 0.58      "     =     3.6  "  0.60      "      =17.2        " 

Undetermined  nitrogen      0.85      "     =     4.9  "  0.27      "     =     7.3       " 


410  METABOLISM,      NUTRITION,     AND     DIET 

Folin  states  this  theory  as  follows:  "It  is  clear  that  the  metabolic  proc- 
esses resulting  in  the  end  products  which  tend  to  be  constant  in  quantity 
appear  to  be  indispensable  for  the  continuation  of  life;  or,  to  be  more  defi- 
nite, those  metabolic  processes  probably  constitute  an  essential  part  of  the 
activity  which  distinguishes  living  cells  from  dead  ones.  I  would  therefore 
call  the  protein  metabolism  which  tends  to  be  constant,  tissue  metabolism, 
or  endogenous  metabolism;  the  other,  the  variable  protein  metabolism,  I  would 
call  the  exogenous  or  intermediate  metabolism. 

"The  endogenous  metabolism  sets  a  limit  to  the  lowest  level  of  nitrogen 
equilibrium  attainable.  Just  where  that  level  is  fixed  will  depend  on  how 
much,  if  any,  urea  is  derived  from  the  same  catabolic  processes  that  produce 
the  creatinin.  If  this  can  be  determined,  we  shall  have  a  formula  expressing 
more  or  less  definitely  the  point  of  lowest  attainable  protein  catabolism, 
because  at  such  a  point  the  percentage  composition  of  the  urine  should  be 
practically  constant.  The  total  nitrogen  eliminated  when  this  constant  com- 
position of  the  urine  has  been  reached  will  indicate  the  lowest  attainable 
level  of  nitrogen  equilibrium." 

The  condition  of  nitrogenous  equilibrium,  therefore,  is  one  which  may 
be  maintained  even  if  the  amount  of  proteid  taken  as  diet  far  exceeds  the 
necessities  of  the  economy,  the  urea  being  excreted  in  excessive  amount;  and 
the  wasteful  use  of  proteid  food  which  is  so  common  may  not  be  attended 
with  harmful  consequences,  so  long  as  the  excreting  organs  are  able  to  elimi- 
nate nitrogen  from  the  body. 

It  is  only  in  cases  of  growth,  by  putting  on  of  flesh,  as  in  growing  children, 
that  nitrogen  is  retained  in  the  body  in  health,  except  to  a  very  small  amount. 
According  to  calculations  which  have  been  made,  it  appears  that  the  body 
puts  on  thirty  grams  of  flesh  for  every  gram  of  nitrogen  so  retained. 

Proteids  as  Fat-  and  as  Glycogen-Formers.  Proteid  food  is  un- 
doubtedly a  source  of  energy  in  the  body ;  and  one  can  say  that  such  proteid 
as  is,  according  to  Yoit's  view,  metabolized  without  becoming  part  of  the 
tissue  may  be  considered  a  source  of  energy.  If  this  be  true,  one  might  ex- 
pect that  proteids  could  be  metabolized  into  other  forms,  such  as  carbo- 
hydrates and  fats.  Bernard  long  ago  stated  that  proteid  was  a  glycogen- 
former;  that  abundant  glycogen  was  stored  in  the  liver  when  flesh  diet  wras 
fed,  and  argued  that  proteid  was  the  source  of  the  glycogen.  The  careful 
work  of  a  number  of  investigators  has  not  obtained  sufficient  evidence  to 
clear  up  this  question  absolutely,  but  the  weight  of  evidence  is  in  favor  of  the 
view  that  in  the  body  sugar  can  be  formed  from  proteids.  Whether  or  not 
proteid  can  be  metabolized  into  fat,  and  stored  as  such,  seems  at  present  an 
open  question,  notwithstanding  the  immense  amount  of  work  expended  in 
trying  to  solve  the  problem. 

Cramer  fed  450  grams  of  lean  meat  per  day  to  a  cat  in  a  respiration  cham- 
ber for  8  days.     The  daily  excretion  of  nitrogen  was  13  grams,  of  carbon 


THE     EFFECT    OF    AN     ALBUMINOID     DIET  41  1 

34.3  grams;  calculating  the  amount  of  carbon  in  the  food  as  41.6  grams 
daily,  this  would  leave  7.3  grams  retained.  This  carbon  might  be  stored  in 
the  form  of  glycogen  or  as  fat.  Calculated  as  glycogen,  it  gives  an  amount 
greater  than  an  animal  of  that  size  could  retain.  Therefore,  the  probabilities 
are  that  the  carbon  is  deposited  in  the  form  of  fat. 

In  the  examination  of  the  fat  formed  in  the  larvae  of  blow-rlies  developing 
in  a  quantity  of  coagulated  blood,  Hoffmann  found  ten  times  more  fat  than 
existed  in  the  blood.  These  experiments  point  in  the  direction  of  fat  for- 
mation from  proteid. 

The  Effect  of  an  Albuminoid  Diet.  The  albuminoid  eaten  in  great- 
est quantity  is  gelatin.  Though  gelatin  closely  resembles  the  proteid  mole- 
cule chemically,  it  cannot  replace  the  proteid  of  the  food.  In  other  words, 
nitrogenous  equilibrium  cannot  be  maintained  on  a  diet  consisting  of  gelatin, 
carbohydrates,  and  fats.  Proteid  food  is  absolutely  essential  to  the  reconstruc- 
tion of  the  proteid  molecule.  Gelatin  is  one  of  the  proteid-like  substances 
whose  food  value  is  comparable  to  that  of  carbohydrates  and  fats,  as  the 
following  experiments  will  prove :  On  a  diet  of  500  grams  of  meat,  without  any 
gelatin,  the  subject  lost  nitrogen  to  the  equivalent  of  22  grams  of  proteid,  but 
when  200  grams  of  gelatin  were  added  the  subject  gained  54  grams.  In  another 
experiment,  when  the  diet  consisted  of  2,000  grams  of  meat  without  gelatin, 
the  gain  was  the  equivalent  of  30  grams  of  proteid,  but  when  200  grams  of 
gelatin  were  added  the  gain  became  376  grams.  The  lack  of  real  proteid 
food  value  is  proven  by  still  a  third  experiment  in  which  the  diet  consisted 
at  first  of  200  grams  each  of  meat  and  of  gelatin;  here  the  gain  was  the  equiva- 
lent of  25  grams  of  proteid,  but,  when  the  meat  was  omitted  and  the  gelatin 
alone  given,  there  was  a  loss  of  118  grams.  In  these  cases  gelatin  did  not 
take  the  place  of  proteid  in  any  sense,  but  rather  saved  it  from  oxidation  as 
a  source  of  energy.  The  proteid  was  so  protected  that,  instead  of  being  used 
up,  it  helped  to  form  tissue  and  increased  the  body  weight.  Gelatin,  there- 
fore, saves  proteid  material  for  constructive  processes. 

Formation  of  Urea.  The  nitrogenous  fraction  of  the  proteid  molecule 
is  in  the  end  converted  largely  into  urea  and  is  excreted  from  the  body  in 
that  form,  as  described  in  the  chapter  on  Excretion.  The  method  of  forma- 
tion of  urea,  as  well  as  the  place  where  this  occurs,  has  given  rise  to  great 
controversy,  while  the  intermediate  products  between  proteids  and  urea 
have  not  as  yet  been  fully  determined.  We  can  state  with  certainty  that 
urea  is  not  formed  in  the  kidneys,  since  it  is  not  only  found  in  the  blood  of 
the  renal  artery,  but  it  accumulates  in  the  blood  if  the  kidneys  are  diseased 
or  removed  and  the  separation  of  the  urine  is  interfered  with.  Circulation 
of  blood  through  the  kidney  does  not  result  in  the  formation  of  more  urea 
than  is  present  in  the  blood  to  begin  with. 

There  are  a  number  of  experiments  that  prove  that  urea  is  formed  in  the 
liver.     The  power  of  the  liver  cells  to  form  urea  is  shown  by  the  increase  of 


412  METABOLISM,     NUTRITION,     AND     DIET 

urea  in  the  blood  leaving  an  isolated  living  liver  through  which  an  artificial 
circulation  is  kept  up.  When  ammonium  carbamate  and  other  ammonium 
salts  are  added  to  the  blood,  the  urea  increases  more  rapidly  and  to  a  greater 
extent.  This  change  occurs  even  when  the  living  hepatic  tissue  is  chopped 
up  and  simply  mixed  with  the  ammonium  compounds  in  a  beaker. 

If  blood  from  a  well-fed  animal  be  circulated  through  the  isolated  liver, 
there  is  a  distinct  increase  in  the  amount  of  urea  it  contains.  On  the  other 
hand,  if  the  blood  be  from  a  fasting  animal  there  is  little  or  no  increase  of 
urea.  Evidently,  then,  the  blood  from  a  well-fed  animal  contains  something 
which  the  liver  cells  are  capable  of  transforming  into  urea.  And,  finally,  if 
the  liver  be  removed  and  the  animal  kept  alive,  as  has  been  done  by  Pawlow, 
there  is  a  marked  diminution  in  the  quantity  of  urea  in  the  urine.  The 
power  of  the  liver  to  form  urea  is  thus  demonstrated.  The  question  which 
now  presents  itself  is,  what  is  this  antecedent  substance  or  substances? 

It  has  already  been  indicated  that  urea  follows  closely  the  amount  of 
proteid  taken  with  the  food,  hence  we  must  look  directly  to  the  nitrogenous 
fraction  of  proteid  cleavage  as  the  final  source  of  urea.  While  the  different 
steps  in  the  process  of  cleavage,  probably  hydrolytic  (Folin),  are  yet  very 
obscure,  still  it  is  believed  that  proteids  are  first  broken  down  to  an  ammonia 
stage  and  then  again  built  up  into  urea  by  the  liver.  It  is  now  believed  that 
ammonium  carbamate  is  at  least  one  true  antecedent  of  urea. 

In  these  experiments  the  liver  is  first  shut  out  of  the  general  circulation 
by  an  Eck's  fistula  connecting  the  portal  vein  with  the  vena  cava.  This 
operation  cuts  off  the  chief  blood  supply  of  the  liver,  viz.,  the  portal  blood, 
but  it  leaves  the  small  hepatic  artery  with  its  oxygen  supply  to  the  liver. 
When  animals  survive  this  operation  it  is  found  that  they  can  live  only  when 
fed  very  carefully  on  a  mixed  diet  from  which  proteids  are  almost  entirely 
eliminated,  and  that,  if  the  food  contain  an  excess  of  proteids,  convulsions 
ensue  with  fatal  termination.  Investigation  of  the  composition  of  the  urine 
and  of  the  blood,  with  the  Eck's  fistula,  shows  that  the  end  product  of  proteid 
metabolism  is  represented  by  ammonium  carbamate  and  that  there  is  a  con- 
siderable decrease  in  urea.  If  ammonium  carbamate  is  injected  into  the 
blood  of  normal  animals  in  a  larger  quantity  than  the  liver  can  dispose  of, 
death  ensues,  following  convulsions  of  the  same  nature  as  those  produced 
by  an  excess  of  proteid  food  in  the  animals  operated  on.  Ammonium  car- 
bamate is  shown  to  be,  in  part  at  least,  the  direct  antecedent  of  urea;  it  is  also 
shown  to  be  a  toxic  substance  which  may  cause  death  by  accumulating  in 
excess.  The  reaction  by  which  the  liver  changes  it  to  the  inert  form  of  urea 
is  as  follows: 


NH2 

NHS 

/ 

/ 

CO 

-     H20   = 

=   CO 

\ 

\ 

OHH4 

NH. 

Ammonium  carbamate.  Urea 


FORMATION    OF    URIC    ACID  413 

The  steps  by  which  absorbed  proteids  are  changed  to  ammonium  car- 
bamate, etc.,  are  as  yet  undecided.  According  to  one  view,  while  still  in  the  cir- 
culating medium,  they  are  metabolized  by  direct  contact  with  the  living  bio- 
plasm of  the  tissues;  according  to  another,  they  must  first  be  incorporated 
into  the  substance  of  the  body  tissues  and  then  changed.  The  intermediate 
steps  occur  chiefly  in  the  intestinal  tract  and  in  muscle  tissue,  and  there  is 
good  reason  to  suppose  that  some  of  the  steps  are  represented  by  various 
extractives  which  are  formed  in  these  regions.  These  substances  probably 
break  down  into  carbon  dioxide,  ammonia,  and  amido-acids,  and  are  then 
built  up  by  synthetic  processes  into  ammonium  carbamate.  Another  possible 
antecedent  is  ammonium  lactate;  this  is  derived  from  the  lactic  acid  which 
is  produced  in  large  quantities  in  the  muscles.  The  elimination  of  urea  is 
increased  very  slightly  by  muscular  activity.  But  there  is  no  direct  relation- 
ship between  the  amount  of  work  done  and  the  amount  of  nitrogen  excreted 
as  urea. 

There  is  experimental  evidence  to  show  that  while  the  liver  produces  the 
major  part  of  the  urea  eliminated,  other  organs  or  tissues  are  capable  of 
forming  it  to  a  limited  degree. 

Formation  of  Uric  Acid.  The  relations  which  uric  acid  and  urea  bear 
to  each  other  in  different  animals,  as  we  have  seen,  is  still  obscure.  The 
fact  that  they  exist  together  in  the  same  urine  makes  it  seem  probable  that 
they  have  different  origins.  The  entire  replacement  of  one  by  the  other,  as 
of  urea  by  uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects,  and  of 
uric  acid  by  urea,  in  the  urine  of  the  feline  tribe  of  mammals,  shows  their 
close  relationship.  But  although  it  is  true  that  one  molecule  of  uric  acid 
is  capable  of  splitting  up  into  two  molecules  of  urea  and  one  of  mes-oxalic 
acid,  this  is  not  evidence  that  uric  acid  is  an  antecedent  of  urea  in  the 
nitrogenous  metabolism  of  the  body.  The  chemical  structure  of  the  uric 
acid  shows  it  has  a  nucleus  of  purin,  and  therefore  is  a  close  relative  of 
adenin,  guanin,  hypoxanthin,  xanthin,  theobromin,  caffein,  etc.  The  nucleins 
on  cleavage  yield  members  of  this  group,  hence  may  be  looked  to  as  the 
primary  source  of  uric  acid  in  man.  Uric  acid,  according  to  Chittenden, 
has  a  double  origin — endogenous  from  nuclear  metabolism,  and  exogenous 
from  metabolism  of  foods  rich  in  nuclear  and  other  purin  compounds.  In 
man,  at  least,  the  uric  acid  is  to  be  ascribed  to  these  two  sources. 

Operative  experiments  on  birds  tend  to  show  that  the  final  step  in  uric- 
acid  formation  takes  place  chiefly  in  the  liver,  for  on  the  removal  of  this  organ 
other  nitrogenous  compounds,  i.e.,  lactates,  accumulate  in  the  blood. 

Hippuric  Acid,  Creatinin,  etc.  The  hippuric  acid  found  in  the 
urine  is  derived  in  part  from  some  constituents  of  vegetable  diet,  though  man 
has  no  hippuric  acid,  as  such,  in  his  food,  nor,  commonly,  any  benzoic  acid  that 
might  be  converted  into  it.  It  is  derived  in  part  from  the  natural  disintegra- 
tion of  tissues,  independent  of  vegetable  food.     Weismann  constantly  found 


414 


METABOLISM,     NUTRITION,     AND     DIET 


an  appreciable  quantity,  even  when  living  on  an  exclusively  animal  diet. 
Hippuric  acid  is  formed  from  the  union  of  benzoic  acid  with  glycin 
(C2H5N02  -f  C7H602  =  C9H9  N03  -f  H20),  which  union  takes  place  under 
experimental  conditions  in  the  kidneys  themselves. 

The  source  of  the  nitrogenous  extractives  of  the  urine  is  chiefly  from  the 
metabolism  of  the  nitrogenous  foods  and  tissues,  but  we  are  unable  to  say 
whether  these  nitrogenous  bodies  have  merely  resisted  further  decomposition 
into  urea,  or  whether  they  are  the  representatives  of  the  decomposition  of 
special  tissues,  or  of  special  forms  of  metabolism  of  the  tissues.  There  is, 
however,  one  exception,  and  that  is  in  the  case  of  creatinin.  This  represents 
not  only  the  creatinin  which  enters  the  body  in  ordinary  flesh  food,  but  is  a 
nitrogenous  waste  which  Folin  regards  as  a  measure  of  muscle  metabolism. 
The  creatinin  eliminated  is  almost  a  constant  quantity  in  a  given  individual, 
irrespective  of  the  quantity  of  proteid  in  the  diet.  Koch  has  attempted  to 
trace  a  quantitative  relation  of  creatinin  excretion  to  lecithin  in  the  food. 

THE  METABOLISM  OF  FATS. 

Fats,  with  carbohydrates,  are  the  direct  source  of  most  of  the  energy 
manifested  by  the  body,  a  fact  demonstrated  by  numerous  observations. 

The  Energy  Value  of  Fats  in  Metabolism.  Fats,  in  comparison 
with  other  food  principles,  are  of  especial  value  as  sources  of  energy.  They 
are  completely  oxidized  in  the  body  to  carbon  dioxide  and  water,  and  yield, 
therefore,  as  much  energy  to  the  body  as  they  yield  upon  oxidation  outside 
the  body.  The  energy  equivalent  of  one  gram  of  fat  is  9.3  large  Calories, 
more  than  twice  that  of  starch  or  of  proteid,  which  in  the  body  yield  only 
4.1  Calories  each  per  gram. 

A  study  of  the  elimination  of  nitrogen  and  of  carbon  during  fasting  shows 
that  the  fats  contribute  to  energy  formation  for  many  days.  This  is  illus- 
trated by  the  following  computation  by  Voit: 


Metabolism  in  a  Dog  during  Fasting.     (Voit.) 


Loss  per  Kilogram  of  Live  Weight. 


Proteids 
in  Grams. 


Fats 
in  Grams. 


Total 
Weight. 


Second  day 2.21 

Fifth  day I-I3 

Eighth  day 0.96 


2.62 
3-25 
3-25 


32.87 
31.67 

3°-54 


The  amount  of  fat  metabolized  is  sharply  influenced  by  the  amount  and  kind 
of  other  food.  For  example,  if  the  amount  of  fat  metabolized  per  day  in 
fasting  is  first  determined,  then  a  ration  of  proteid  given  for  a  few  days, 
followed  by  a  second  fasting  period,  it  will  be  found  that  the  metabolism  of 


SOURCE     OF     THE     BODY     FAT 


415 


body  fat  is  sharply  increased  in   the  second   period,  due  to  the  stimulating 
influence  of  the  proteid. 

This  is  demonstrated  by  the  following  determination  of  Rubner: 


Food  of  Dog. 
(Rubner.) 

Nitrogen  of 
Food. 

Nitrogen 
Excreted. 

Body  Fat 
Metabolized. 

O 

C. 

4.38 

49-33 

415  grams  lean  meat 

14. 11 

^-Z2 

25.44  average 

0 

0. 

2.8o 

70-04 

760  grams  lean  meat 

25.16 

20.63 

30.73  first  two  days 

The  fat  of  the  ordinary  daily  diet  is  absorbed  into  the  blood  and  no  doubt 
contributes  directly  to  oxidation  processes.  Just  the  steps  in  this  oxidation 
process  cannot  at  present  be  given.  If  the  fat  food  is  insufficient,  then  the 
body  store  is  drawn  upon ;  if  in  excess,  then  it  is  stored  in  the  bodv. 

Source  of  the  Body  Fat.  Excess  of  fat  in  the  food  can  be  stored 
as  fat  in  the  body.  This  fact  is  demonstrated  by  Voit,  Hoffmann,  Rubner, 
and  others.  Rubner  states  that  82  to  92  per  cent  of  the  fat  excess  can  be 
stored.  The  fat  stored  is  of  the  same  kind  given  in  the  food,  even  though 
the  usual  fat  of  the  animal  is  different.  The  melting  point  of  dog's  fat  is 
about  200  C,  but  by  feeding  an  excess  of  mutton  fat  the  melting  point  has  been 
raised  to  400  C.  The  subcutaneous  fat  of  pigs  subjected  to  this  experi- 
ment is  more  or  less  fluid  according  to  the  melting  point  of  the  fat  fed. 

The  body  fat  can  also  be  derived  from  carbohydrate  food,  a  fact  which 
the  practices  of  the  stock  feeder  and  dairyman  constantly  verify.  Two  ex- 
periments will  present  the  matter  more  vividly  than  pages  of  description. 


Gain  in  Fat  of  a  Pig  Fed  on  Rice.     (Meissl  and  Strohmer.) 


Pig  Weight. 

Rice  Fed 
Daily. 

Fat  in 
Food. 

Proteid 
in  Food. 

Proteid 
Gain. 

Carbon 
Gain. 

Net  Gain 
in  Carbon. 

140  kgm. 

2  kgm. 

5-3  gm- 

104  gm. 

38  gm- 

289  gm. 

269  gm. 

It  is  obvious  that  the  5.3  grams  of  fat  and  the  66  grams  of  proteid  cannot 
account  for  the  carbon  retained,  and  one  must  look  to  the  carbohydrate  as 
the  source  of  the  fat. 

Jordan  placed  a  Jersey  cow  on  a  feed  of  hay  and  grain  from  which  the 
fat  was  extracted.  The  cow  in  95  days  assimilated  5.7  pounds  of  fat,  in- 
creased 47  pounds  in  weight,  and  produced  62.9  pounds  of  fat  in  the  milk. 
The  nitrogen  excreted  was  the  equivalent  of  33.3  pounds  of  proteid.  The 
non-nitrogenous  moiety  of  the  proteid,  if  its  carbon  had  all  gone  into  fat, 
could  not  have  produced  over  17  pounds.     Summarized,  this  experiment 


416  METABOLISM,    NUTftlTlON,    AND     DIET 

shows  conclusively  that  fat  is  synthesized  from  carbohydrate.  It  requires 
about  2.7  grams  of  dextrose  to  form  1  gram  of  fat,  and  this  condensation 
takes  place  with  the  formation  of  carbon  dioxide  and  water  and  the  libera- 
tion of  about  15  per  cent  of  the  available  heat  of  oxidation. 

Persistent  excess  of  carbohydrate  food  produces  an  accumulation  of  fat, 
which  may  not  only  be  an  inconvenience  causing  obesity,  but  may  interfere 
with  the  proper  nutrition  of  muscles,  produce  a  feebleness  of  the  action  of 
the  heart,  and  other  troubles. 

The  formation  of  fat  from  proteid  is  discussed  on  page  410. 

Obesity  is  a  condition  of  excessive  storage  of  fats.  In  many  of  these 
cases  there  is  persistent  storing  of  fat  in  the  presence  of  a  diet  of  low  energy 
value  and  with  considerable  physical  labor.  It  seems  that  such  persons 
must  have  a  very  economic  protoplasmic  metabolism,  a  biological  factor  that 
lacks  sufficient  explanation. 

THE  METABOLISM  OF  CARBOHYDRATES. 

Energy  Value.  The  nutritive  function  of  carbohydrates  in  the  body 
is  to  serve  as  a  source  of  energy.  They  are  oxidized,  with  the  ultimate  pro- 
duction of  carbon  dioxide  and  water,  and  must  liberate  the  same  amount 
of  energy  as  when  burned  outside  the  body,  i.e.,  4.1  Calories.  A  given 
weight  of  dextrose,  therefore,  furnishes  much  less  energy  than  a  correspond- 
ing weight  of  fat. 

Carbohydrates  are  strictly  energy-formers  and  may  be  regarded  as  the 
immediate  source  of  the  energy  of  oxidations,  while  fats  are  reserves  drawn 
on  only  after  the  carbohydrates  are  used  up.  Dextrose  is  a  constant  constitu- 
ent of  the  blood  to  the  extent  of  about  1  to  1.5  per  cent.  When  this  percentage 
is  increased  above  2.5,  the  dextrose  is  either  stored  as  glycogen,  i.e.,  in  the 
case  of  the  portal  blood  during  the  absorption  of  a  carbohydrate  meal,  or 
eliminated  by  the  kidney,  i.e.,  in  diabetes. 

The  Formation  of  Glycogen — Glycogenesis.  The  important  fact 
that  the  liver  normally  forms  sugar,  or  a  substance  readily  convertible 
into  it,  was  discovered  by  Claude  Bernard  in  the  following  way:  He  fed  a 
dog  for  seven  days  with  food  containing  a  large  quantity  of  sugar  and  starch; 
and,  as  might  be  expected,  found  sugar  in  both  the  portal  and  hepatic  blood. 
But  when  the  dog  was  fed  with  meat  only,  to  his  surprise,  sugar  was  still 
found  in  the  blood  of  the  hepatic  veins.  Repeated  experiments  gave  in- 
variably the  same  result.  No  excess  of  sugar  was  found  in  the  portal  vein 
under  a  meat  diet,  if  care  was  taken  to  prevent  reflux  of  blood  from  the  hepatic 
venous  system.  Bernard  found  sugar  also  in  the  substance  of  the  liver.  It 
thus  seemed  certain  that  the  liver  formed  sugar  even  when,  from  the  absence 
of  saccharine  and  amyloid  matters  in  the  food,  none  could  be  brought  directly 
to  it  from  the  stomach  or  intestines. 


SOURCE     OF     GLYCOGEN  417 

Bernard  subsequently  found  that  a  liver  removed  from  the  body,  and 
from  which  all  sugar  had  been  completely  washed  away  by  injecting  a  stream 
of  water  through  its  blood-vessels,  contained  sugar  in  abundance  after  the 
lapse  of  a  few  hours.  This  post-mortem  production  of  sugar  was  a  fact 
which  could  be  explained  only  on  the  supposition  that  the  liver  contained  a 
substance  readily  convertible  into  sugar.  This  theory  was  proved  correct 
by  the  discovery  of  a  substance  in  the  liver  allied  to  starch,  termed  glycogen. 

Bernard's  brilliant  researches  led  him  to  announce  the  theory  that  the 
carbohydrate  which  is  periodically  absorbed  in  large  amount  is  stored  in  the 
liver  only  to  be  reconverted  to  dextrose  and  discharged  back  into  the  blood 
stream  whenever  the  percentage  falls  below  a  certain  level.  He  regarded  the 
liver  as  a  storehouse  which  regulated  the  blood  dextrose  to  a  constant  level. 
This  is  the  glycogenic  function  of  the  liver. 

Source  of  Glycogen.  The  greatest  amount  of  glycogen  is  produced 
by  the  liver  upon  a  diet  of  starch  or  sugar,  but  a  certain  quantity  is,  or  at 
least  may  be,  produced  upon  a  proteid  diet.  The  glycogen,  when  stored  in 
the  liver  cells,  may  readily  be  demonstrated  in  sections  of  liver  containing  it 
by  its  reaction  (red  or  port-wine  color)  with  iodine,  and,  moreover,  when  the 
hardened  sections  are  so  treated  that  the  glycogen  is  dissolved  out,  the  proto- 
plasm of  the  cell  is  so  vacuolated  as  to  appear  little  more  than  a  framework. 
There  is  no  doubt  that  in  the  liver  of  a  hibernating  frog  the  amount  of  glyco- 
gen stored  up  in  the  liver  cells  is  very  considerable. 

Average  Amount  of  Glycogen  in  the  Liver  of  Dogs  under  Various  Diets.     (Pavy.) 

Diet.  Amount  of  Glycogen  in  the  Liver. 

Flesh  food 7.19  per  cent 

Flesh  food  with  sugar 14 . 5 

Vegetable  diet,  i.e.,  potatoes  with  bread  or  barley  meal J7-23 

The  dependence  of  the  formation  of  glycogen  on  the  kind  of  food  taken 
is  also  shown  by  the  following  results,  obtained  by  the  same  experimenter: 

Average  Quantity  of  Glycogen  Found  in  the  Liver  of   Rabbits  after  Fast- 
ing, and  After  a  Diet  of  Starch  and  Sugar  Respectively. 

After  three  days'  fasting Practically  absent 

"     diet  of  starch  and  grape-sugar 15 .4  per  cent 

"        "        cane-sugar 16.9         " 

Glycogen  is  also  formed  from  fats  in  diabetes,  but  there  is  no  clear  proof 
that  fats  increase  the  amount  of  glycogen  in  the  cells.  Glycerin  injected  into 
the  alimentary  canal  may  also  increase  the  glycogen  of  the  liver.  The  diet 
most  favorable  to  the  production  of  a  large  amount  of  glycogen  is  a  mixed 
diet  containing  a  large  amount  of  carbohydrate,  but  with  some  proteid. 

Glycogen  is  stored  in  other  organs  of  the  body.  Of  these  the  muscles 
are  deserving  of  special  mention.  The  amount  of  glycogen  in  the  muscles 
27 


418  METABOLISM,    NUTRITION,     AND     DIET 

of  young  animals  is  often  considerable.  The  placenta  is  also  a  storehouse 
of  glycogen. 

The  Destination  of  Glycogen.  The  chief  theories  concerning  the 
use  of  glycogen  in  the  organism  are  advanced  by  Bernard  and  by  Pavy. 
The  former  considers  glycogen  as  a  reserve  supply  of  carbohydrate.  When- 
ever the  glycogen  of  the  blood  is  reduced  below  the  normal  level,  i.e.,  about 
o.i  to  0.15  per  cent,  there  is  a  conversion  of  glycogen  into  sugar.  The  sugar 
enters  the  blood  and  passes  to  the  tissues  where  its  oxidation  is  a  source  of 
energy.  Pavy  considers  glycogen  to  be  a  stage  in  the  synthesis  of  carbohydrate 
to  fat  and  proteid.  Bernard's  theory  is  more  generally  accepted.  It  ex- 
plains more  satisfactorily  why  the  sugar  content  of  the  blood  is  so  constant. 
The  conversion  of  glycogen  to  sugar  takes  place  by  the  action  of  an  intracellu- 
lar ferment  in  the  glycogenic  cells.  Such  an  enzyme  has  been  isolated  for 
the  liver.  It  is  this  enzyme  that  converts  the  liver  glycogen  to  dextrose  after 
death,  and  which  is  destroyed  by  boiling  in  the  usual  process  of  isolating 
glycogen. 

Glycosuria.  Sugar  may  be  present  to  excess  not  only  in  the  hepatic 
veins,  but  in  the  systemic  blood.  When  such  is  the  case,  the  sugar  is  ex- 
creted by  the  kidneys,  and  appears  in  variable  quantities  in  the  urine.  This 
condition  is  known  as  glycosuria. 

Glycosuria  may  be  experimentally  produced  by  puncture  of  the  medulla 
oblongata  in  the  region  of  the  vaso-motor  center,  puncture  diabetes.  The 
better  fed  the  animal,  the  larger  is  the  amount  of  sugar  found  in  the  urine 
following  this  operation.  In  the  case  of  a  starving  animal  no  sugar  appears. 
It  is,  therefore,  highly  probable  that  the  sugar  comes  from  the  hepatic  glyco- 
gen, since  in  the  one  case  glycogen  is  in  excess,  and  in  the  other  it  is  almost 
absent.  The  nature  of  the  influence  is  uncertain.  This  influence  may  be 
exercised  in  dilating  the  hepatic  vessels,  or  possibly  may  be  exerted  on  the 
liver  cells  themselves. 

Many  other  circumstances  will  cause  glycosuria.  It  has  been  observed 
after  the  administration  of  various  drugs,  e.g.,  strychnine;  phloridzin,  a  glu- 
coside,  and  its  derivative  phloretin,  which  is  not  a  glucoside;  morphine; 
adrenalin;  nitrite  of  amyl,  etc.;  after  the  injection  of  curari,  poisoning  with 
carbonic-oxide  gas,  the  inhalation  of  ether,  chloroform,  etc.,  the  injection  of 
oxygenated  blood  into  the  portal  venous  system.  Glycosuria  has  been 
observed  in  man  after  injuries  to  the  head  and  in  the  course  of  various 
diseases.  In  such  cases  the  glycosuria1  appears  to  be  due  either  to  some  ab- 
normal activity  of  the  liver  cells  themselves  or  to  an  interference  with  the 
normal  metabolism  of  the  carbohydrate  group.  In  this  latter  case  it  is  pos- 
sible that  the  usual  complete  oxidation  of  carbohydrate  is  interfered  with. 

The  well-known  disease,  diabetes  mellitus,  in  which  a  large  quantity  of 
sugar  is  persistently  excreted  daily  with  the  urine,  has,  doubtless,  some  close 
relation  to  the  normal  functions  of  the  pancreas.     The  nature  of  the  relation- 


MINERAL     MATTERS,     WATER,     ETC. 


419 


ship  has  not  yet  been  determined,  though  some  recent  experiments  seem  to 
be  pertinent,  page  431. 

Mineral  Matters,  Water,  etc.  The  chief  mineral  constituents  of 
the  foods  are  sodium,  potassium,  calcium,  magnesium,  and  iron,  together 
with  chlorine,  sulphur,  and  phosphorus.  The  inorganic  substances  are  not 
a  source  of  heat.  They  may  supply  a  certain  amount  of  energy,  as  osmotic 
energy,  but  this  is  of  no  significance  as  compared  with  their  influence  on  the 
metabolism  of  organic  substances.  An  animal  fed  on  a  normal  food  deprived 
of  the  mineral  constituents  survives  only  a  few  weeks  at  most. 

The  amount  of  mineral  matter  in  the  tissues  of  the  human  body,  exclusive 
of  the  skeletal  parts,  is  about  one  per  cent.  It  is  safe  to  say  that  this  is  chiefly 
in  complex  organic  combination  in  the  body.  The  daily  quantity  excreted 
is  about  twenty  to  thirty  grains.  This  quantity  enters  the  body  in  the  food, 
chiefly  in  combination  with  complex  compounds.  It  is  a  question  as  to  what 
per  cent  of  inorganic  salts,  like  the  calcium,  the  phosphates,  and  the  iron, 
is  available  when  taken  into  the  body  in  inorganic  form. 

We  have  discussed  in  previous  chapters  the  role  of  certain  salts  in 
their  influence  on  metabolism;  for  example,  of  sodium,  potassium,  calcium, 
iron,  etc.  Foods  like  milk  and  eggs  are  especially  rich  in  calcium  and 
phosphorus,  and  are  particularly  desirable  for  young  children,  the  for- 
mer for  its  influence  on  the  growth  of  the  skeleton,  the  latter  for  the  same 
reason  and  as  a  stimulator  of  growth  of  protoplasm  in  general.  Lack  of 
mineral  constituents,  especially  calcium  compounds,  in  food  shows  its  in- 
fluence on  metabolism  in  the  disease  known  as  rickets. 

Investigations  are  in  progress  at  the  present  time  which  may  demonstrate 
more  fully  the  specific  influence  of  phosphorus  on  animal  nutrition  and  on 
growth.     Tunnicliff  has  just  demonstrated  that  an  increase  of  the  phos- 

Nutrition  Experiment  in  Fiye-months-old  Pigs.     (E.  B.  Forbes.) 


Rations. 


Hominy,  blood  flour;  bran  ex- 
tract. (Phosphorus  mostly 
as  phytin) 

Hominy;  blood  flour;  bone  flour. 
(Phosphorus  mostly  as  tri- 
calcic  phosphate) 

Hominy;  blood  flour.  (Low- 
phosphorus  ration) 


Per  cent  Gain 
in  Live  Weight 
in  60  Days' 
Feeding. 


69.I 

6r.o 

41.6 


Per  cent  Gain  in  Certain  Tissues 
Corresponding  to  One  per  Cent 
Gain  in  Live  Weight. 


Psoas 

Muscle. 


.01 


•72 


Ash  of 
Humerus. 


•59 


.08 


Thickness 
of  Back  Fat. 


.64 


1.04 


420 


METABOLISM,     NUTRITION,    AND     DIET 


phorus  content  of  the  food  of  children,  if  given  in  complex  organic  form, 
increases  the  efficiency  of  the  metabolism  of  nitrogen  by  as  much  as  10  per 
cent.  If  given  to  children  as  calcium  phosphate  it  has  no  beneficial  influence 
in  this  regard.  Forbes,  in  his  experiments  on  the  nutrition  of  pigs,  shows 
that  the  individuals  fed  with  food  to  which  phosphorus  was  added,  as  ground 
fresh  bone,  grew  larger  and  stronger  skeletons. 

Percentage  of  Phosphoric  Acid  (P2O5)  in  Some  Fresh  Foods.     (Quoted  from 
Girard,  by  Hutchinson,  in  "  Food  and  Dietetics.") 

Vegetable.  Per  cent. 

Carrot o .  036 

Turnip 0.058 


Cabbage o .  089 

Potato o .  140 

Chestnuts o .  200 

Barley  meal 0.230 


Animal. 
Pork  .... 

Milk 

Beef 


Per  cent. 

.    0 .  1 60 

.    0.220 

.285 


Eggs 0.337 

White  cheese °-374 

Mutton 0.425 


Salts  in  the  body  not  only  take  part  in  the  reactions  themselves,  but  they 
stimulate  in  other  substances  reactions  that  are  of  incalculable  benefit  to 
the  body. 

The  necessity  for  the  taking  of  water  in  order  to  balance  the  daily  excretion, 
is  sufficiently  obvious.     Man  will  live  only  a  few  days  if  deprived  of  water. 

Effects  of  Deprivation  of  Food.  The  animal  body  deprived  of  all 
food  dies  from  starvation  in  the  course  of  a  variable  time.  The  length  of 
time  that  any  given  animal  will  live  in  such  a  condition  depends  upon  many 
circumstances,  the  chief  of  which  are  the  nature  and  activity  of  the  metabolism 
of  its  tissues. 

The  effect  of  starvation  on  the  lower  animals  is,  first  of  all,  as  might  be 
expected,  a  loss  of  weight.  The  loss  is  greatest  at  the  beginning  of  the  de- 
privation period,  but  afterward  decreases  to  a  level  from  which  it  does  not 
vary  much  day  by  day  until  death  ensues.  Chossat  found  that  the  ultimate 
proportional  loss  in  different  animals  experimented  on  was  almost  exactly 
the  same,  death  occurring  when  the  body  had  lost  forty  per  cent  of  its  original 
weight.  Different  parts  of  the  body  lose  weight  in  very  different  proportions. 
The  following  most  noteworthy  losses  are  taken,  in  round  numbers,  from 
the  table  given  by  Chossat: 


Per  Cent. 

Fat 93 

Blood 75 

Spleen 71 

Pancreas 64 


Per  Cent. 

Liver 52 

Muscles 43 

Nervous  tissues 2 


These  figures  are  in  practical  agreement  with  those  of  later  experimenters. 
They  show  that  the  chief  losses  are  sustained  by  the  adipose  tissue,  the  mus- 
cles and  glands. 


EFFECTS     OF     DEPRIVATION    OF    FOOD 


421 


The  effect  of  starvation  on  the  temperature  of  the  various  animals  ex- 
perimented on  by  Chossat  was  very  distinct.  For  some  time  the  variation 
in  the  daily  temperature  was  more  marked  than  its  absolute  and  continuous 
diminution,  the  daily  fluctuation  amounting  to  30  C.  instead  of  0.50  to  i°  C, 
as  in  health.     The  temperature  fell  very  rapidly  a  short  time  before  death, 


z 
< 


3 


60 
55 

50 
45 
40 
35 
30 
25 
20 
15 

10 

5 

I  0 


V 

\ 

""** 

:&-* 

==== 

r-~ 

/             Z             3            4             f            6            7            <S 

, . ' 

DAY 5  OF  FA5T1NG 

Fig.  310. — The  Elimination  of  Urea  by  Dogs  during  Fasting.      (Voit.) 
■™™»™""     Following    2,500  grams  of  meat  in  the  food. 

"  1,500 

minimal  amount  of  proteid  in  the  food. 


and  death  ensued  when  the  loss  had  amounted  to  about  16. 20  C.  It  has  been 
often  said,  and  with  truth,  that  death  by  starvation  is  really  death  from  want 
of  heat.  The  effect  of  the  application  of  external  warmth  to  animals  cold 
and  dying  from  starvation  is  more  effectual  in  reviving  them  than  the  ad- 
ministration of  food. 

The  symptoms  produced  by  starvation  in  the  human  subject  are  hunger,  ac- 
companied, or  it  may  be  replaced,  by  pain,  referred  to  the  region  of  the  stomach; 
insatiable  thirst;  sleeplessness;  general  weakness,  and  emaciation.  The  ex- 
halations both  from  the  lungs  and  from  the  skin  are  fetid,  indicating  the 
tendency  to  decomposition  which  belongs  to  badly  nourished  tissues;  and  death 


422  METABOLISM,    NUTRITION,     AND     DIET 

occurs  often  with  symptoms  of  nervous  disorder,  delirium,  or  convulsions. 
Death  commonly  occurs  within  from  six  to  ten  days  after  total  deprivation 
of  food.  This  period  may  be  considerably  prolonged  by  taking  a  very  small 
quantity  of  food,  or  even  by  water  alone.  The  cases  so  frequently  related 
of  survival  after  many  days  or  even  some  weeks  of  abstinence  have  been  due 
either  to  the  last-mentioned  circumstances,  or  to  other  no  less  effectual  con- 
ditions which  prevented  the  loss  of  heat  and  moisture. 

During  the  starvation  period  the  excretions  diminish.  The  urea,  as  repre- 
senting the  nitrogen,  falls  quickly  in  amount,  reaches  a  minimum  where  it 
remains  constant  for  several  days,  then  finally  falls  rapidly  immediately 
before  death.  The  sulphates  and  phosphates  undergo  much  the  same  type 
of  reduction.  The  carbon  dioxide  given  out  and  the  oxygen  taken  in  di- 
minish. The  feces  diminish,  as  well  as  the  bile.  It  is  highly  probable 
that  the  greater  part  of  the  nitrogen  represents  the  loss  of  weight  of  the 
muscles. 

In  starvation,  then,  we  see  that  the  only  income  consists  of  water  and 
the  inspired  oxygen.  The  whole  of  the  energy  of  the  body  given  out  in  the 
form  of  heat  and  mechanical  labor  is  obtained  at  the  expense  of  its  own 
tissues,  there  being  as  a  result  a  constant  drain  of  the  nitrogen  and  carbon, 
not  to  mention  the  other  elements  of  which  the  tissues  are  composed.  It  is 
obvious  that  such  a  condition  cannot  be  endured  for  any  length  of  time. 

REQUISITES  OF  A  NORMAL  DIET. 

It  will  be  understood  from  the  preceding  discussion  that  it  is  necessary 
that  a  normal  diet  should  be  made  up  of  the  various  classes  of  foods  in  suffi- 
cient quantity  to  supply  the  same  amounts  of  carbon  and  nitrogen  that  are 
gotten  rid  of  by  the  excreta.  No  doubt  these  desiderata  may  be  satisfied 
by  many  combinations  of  foods,  and  it  would  be  unreasonable  to  expect  the 
diet  of  every  adult  to  be  the  same.  The  age,  sex,  strength,  and  circum- 
stances surrounding  each  individual  must  ultimately  determine  what  he 
takes  as  food.  A  dinner  of  bread  and  cheese  with  an  onion  contains  all  the 
requisites  for  a  meal,  but  such  diet  would  be  suitable  only  for  those  possessing 
strong  digestive  powers.  It  is  a  well-known  fact  that  the  diet  of  the  con- 
tinental nations  differs  from  that  of  our  own  country,  and  that  of  cold  from 
that  of  hot  climates,  but  the  same  principle  underlies  all,  viz.,  the  replace- 
ment of  the  losses  of  the  body  in  the  most  convenient  and  economical  way 
possible.  Any  one  in  active  work  requires  more  food  than  one  at  rest,  and 
growing  children  require  less  food  than,  but  a  different  variety,  from  adult 
men  and  women. 

The  chief  diet-scales  which  have  been  drawn  up  with  the  object  of  supply- 
ing the  proximate  principles  in  the  required  proportions  are  given  in  the 
table  below: 


REQUISITES     OF     A     NORMAL     DIET 

Standard   Dietaries. 


423 


Author. 

Proteid. 

Fat. 

Carbohydrate. 

Calories. 

Voit 

Rubner 

Moleschott 

Munk 

Wolff 

118  grams 
127       " 
130       " 
105       " 
125       " 

119  " 
125       " 

56  grams 
52       " 
40       " 
56      " 
35      " 
51       " 
125      " 

500  grams 
5°9       " 
55°       " 
500       " 

540       " 
531       " 
45°      " 

3>°55 
3.°92 
3,160 
3,022 

3.030 
3,!4o 
3,520 

Playfair 

Atwater 

Average 

121  grams                59  grams 

510  grams 

3,i35 

The  basis  of  these  diets  is  to  supply  the  necessary  proteid  nitrogen  first 
of  all,  and,  second,  to  supply  enough  potential  energy  to  balance  the  energy 
expended  per  day. 

The  amount  of  the  excreted  carbon  and  nitrogen  is  not  always  the  same. 
It  has  been  proved  possible,  for  example,  to  subsist  on  9  or  10  grams  of  nitro- 
gen and  200  grams  of  carbon  per  diem,  the  ordinary  diet  for  needle-women 
in  London,  and  the  average  of  the  cotton  operatives  in  Lancashire  during  the 
famine,  1862.  The  amount  of  these  elements  excreted  falls  to  figures  cor- 
responding to  such  an  income.  Of  course,  upon  such  a  diet  the  metabolism 
is  low,  and  persistent  physical  weakness  must  be  the  result,  probably  from 
insufficient  carbon.  The  9  or  10  grams  of  nitrogen  in  such  a  semi-starvation 
diet  would  be  equivalent  to  58.5  to  65  grams  of  proteid,  whereas  the  amount 
of  proteid  in  some  diets  may  be  as  high  as  150  and  more  grams  per  day. 
Chittenden's  nutritional  experiments,  so  often  referred  to  in  these  pages, 
have  proven  that  adult  men  can  subsist  in  nitrogenous  equilibrium,  and  do 
vigorous  work  and  maintain  good  health,  on  a  proteid  diet  below  that  given 
in  the  above  example,  i.e.,  on  4  to  10  grams  of  nitrogen.  In  such  diets  a 
plentiful  supply  of  carbohydrates  is  permitted. 

Not  only  the  proteids  but  also  the  fats  may  vary.  The  amount  may  be 
as  low  as  35  grams  and  as  high  as  125  grams.  The  carbohydrates  may  vary 
from  200  grams  to  500  grams  and  upward.  Sometimes,  with  a  small  pro- 
portion of  fat,  the  carbohydrate  may  be  correspondingly  increased  to  make 
up  the  necessary  carbon.     A  useful  table,  after  Payen,  will  help  to  show  in 


Table  of  Percentages  of  N  and  C  in  the  Following  Substances. 


n.  c. 

Beef  (without  bone) . .  3.  n. 

Roast  beef 3-528  17-76 

Eggs 1-0  130 

Cow's   milk o.<)C>  8. 

Cheese 2  to  7  35.   to  71 

Beans 4.;  42. 

Lentils 4.1  48. 


N. 

Oatmeal x-95 

Bread 1 . 

Potatoes °-33 

Eels 2 . 

Mackerel 3-74 

Sardines  in  oil 6. 

Butter o .  64 


26 


424  METABOLISM,     NUTRITION,     AND     DIET 

what  ways  it  is  possible  to  obtain  the  requisite  amount  of  nitrogen  and  carbon 
from  the  most  common  food  stuffs. 

In  order  to  obtain  the  amount  of  proteid  present  from  the  proportion  of 
nitrogen,  multiply  by  6.25. 

From  these  data,  or  from  the  composition  of  foods  on  page  298,  it  is  pos- 
sible to  form  various  diet-scales  which  shall  supply  the  needs  of  different 
conditions  of  growth  and  decay  of  the  body.  Assuming  that  the  average 
amount  of  carbon  and  nitrogen  required  is  about  300  grams  and  20  grams 
respectively,  this  may  be  obtained  as  follows: 

N.  C. 

340  grams  (12  oz.  or  f  lb.  avoirdupois)  lean  uncooked  meat*. .    10  grams  37  grams 

906       "       (32  oz.  or  2  lbs.  avoirdupois)  bread 9       "  252      " 

19  grams  289  grams 

But  this  diet  is  not  the  usual  one;  a  certain  proportion  of  the  carbon  is 
usually  supplied  as  butter,  or  bacon,  and  so  if  90  grams  of  butter  or  bacon 
be  used  it  would  supply  about  72  grams  of  carbon,  and  the  carbohydrate 
would  be  diminished  nearly  one-third;  but  the  nitrogen  would  also  be  di- 
minished from  9  grams  to  6  grams.  It  would  be  necessary  to  supply  some 
extra  nitrogenous  principle,  which  might  be  done  by  the  addition  of  eggs, 
milk,  cheese,  beans,  or  of  any  of  the  food-stuffs  already  enumerated  at  page 
298  el  seq.,  as  supplying  nitrogenous  food  chiefly.  For  example,  56  grams 
(2  oz.)  cheese  contain,  on  an  average,  3  grams  of  nitrogen  and  20  grams  of 
carbon;  or  28  grams  cheese,  containing  1.5  grams  of  nitrogen  and  about 
10  grams  carbon,  together  with  225  grams  potatoes  and  225  grams  carrots, 
supplying  about  1  gram  of  nitrogen  and  35  grams  of  carbon,  may  be 
added.     The  diet  would  then  read  as  follows: 

N.  C. 

340  grams  lean  uncooked  meat 10. o  grams  37  grams 

600       "       bread 6.0      "  168      " 

90      "       butter 0.5       "  72       " 

28      "       cheese    1.5       "  10      " 

225       "       potatoes..  ) I0      «  3-       « 

225       "       carrots. . .  (  

19.0  grams  322  grams 

The  30  grams  of  salts  necessary  to  replenish  the  daily  loss  by  excre- 
tion in  the  urine  are  contained  in  the  meat  16  grams,  the  bread  12  grams, 
and  vegetables  about  4  grams. 

The  fluids  should  consist  of  about  2,500  to  2,800  grams,  and  might  be 
given  as  water,  with  or  without  tea,  coffee,  or  cacao,  which  are  chiefly 
stimulants. 

The  Energy  Requirements  of  the  Body.  The  food  must  not  only 
make  up  for  the  substances  eliminated  from  the  body  but  must  also  supply 
the  potential  energy  of  heat  and  motion  set  free  in  the  living  body.     The 

*As  meat  loses  23  to  34  per  cent  in  cooking,  the  weight  of  cooked  meat  would  be 
proportionately  less. 


THE  ENERGY  REQUIREMENTS  OF  THE  BODY  425 

amount  of  heat  is  measured  in  terms  of  calories,  or  more  often  in  large  calories. 
The  work  energy  may  be  expressed  in  gram-centimeters  or  in  kilogrammeters. 
The  heat-unit  calories  may  be  transferred  into  the  work-unit  gramcenti- 
meters  by  multiplying  by  .042,  and  the  converse. 

The  source  of  the  heat  and  work  energy  which  is  produced  in  the  body  is 
from  the  metabolic  changes  of  the  tissues,  the  chief  part  of  which  is  of  the 
nature  of  oxidation,  since  it  may  be  supposed  that  the  oxygen  of  the  atmos- 
phere taken  into  the  system  is  ultimately  combined  with  carbon  and  hydrogen. 
Any  change,  indeed,  which  occurs  in  the  protoplasm  of  the  tissues,  resulting 
in  an  exhibition  of  its  function,  is  attended  by  the  evolution  of  heat  and  the 
formation  of  carbon  dioxide  and  water.  The  more  active  the  changes  the 
greater  is  the  heat  produced.  But,  in  order  that  the  protoplasm  may  per- 
form its  function,  the  waste  of  its  own  destructive  metabolism  must  be  re- 
paired by  the  due  supply  of  food  material  to  be  built  up  in  some  way  into  the 
protoplasmic  molecule.  Food  is  therefore  necessary  for  the  production  of 
heat.  In  the  tissues,  as  we  have  several  times  remarked,  two  processes  are 
continually  going  on:  the  building  up  of  the  protoplasm  from  the  food,  anab- 
olism,  which  is  not  accompanied  by  the  evolution  of  heat,  and  the  oxidation 
of  the  protoplastic  materials,  catabolism,  resulting  in  the  production  of  energy, 
by  which  heat  is  set  free.  It  is  not  necessary  to  assume  that  the  combustion 
processes,  indeed,  are  as  simple  as  the  bare  statement  of  the  fact  might  seem 
to  indicate.  But  complicated  as  the  various  stages  may  be,  the  ultimate  re- 
sult is  as  simple  as  in  ordinary  combustion  outside  the  body,  and  the  prod- 
ucts are  the  same. 

This  theory,  that  the  maintenance  of  the  temperature  of  the  living  body 
depends  on  continual  chemical  change,  chiefly  by  oxidation  of  combustible 
materials  in  the  tissues  or  by  the  tissues,  has  long  been  established.  The 
quantity  of  carbon  and  hydrogen  supplied  as  food,  which,  in  a  given  time, 
unites  in  the  body  with  oxygen,  is  sufficient  to  account  for  the  amount  of  heat 
generated  in  the  animal  within  the  same  period,  page  406;  an  amount  capable 
of  maintaining  the  temperature  of  the  body  at  from  36. 8°  to  38.70  C,  not- 
withstanding a  large  loss  by  radiation  and  evaporation.  This  estimation 
depends  upon  the  chemical  axiom  that  when  a  body  undergoes  a  chemical 
change  the  amount  of  energy  set  free  is  the  same,  supposing  the  resulting 
products  are  the  same,  whether  the  change  takes  place  suddenly  or  gradually. 
If  a  certain  number  of  grams  of  different  substances  are  introduced  as  food, 
and  if  they  undergo  complete  oxidation,  the  amount  of  kinetic  energy,  as 
shown  in  the  amount  of  heat  and  mechanical  work,  is  the  same  as  would  be 
developed  if  the  same  bodies  were  completely  oxidized  outside  the  body. 
If  one  gram  of  fat  be  taken  into  the  body  and  is  completely  oxidized,  result- 
ing in  the  production  of  a  definite  amount  of  carbon  dioxide  and  water,  it 
may  be  supposed  to  have  produced  the  same  amount  of  heat  as  it  would  have 
produced  outside  the  body.  In  the  case  of  proteid  food  it  is  a  little  different, 


426  METABOLISM,     NUTRITION,    AND     DIET 

since  it  is  never  completely  oxidized  within  the  body,  but  may  be  supposed 
to  give  rise  to  a  definite  amount  of  urea,  not  a  completely  oxidized  body. 
In  this  case  the  gram  of  proteid  may  be  considered  to  perform  the  same 
amount  of  heat  as  the  proteid  would  outside  the  body  minus  the  amount 
which  would  be  obtained  from  the  complete  oxidation  of  the  resulting  urea. 

The  actual  amount  of  heat  produced  per  diem  has  been  experimentally 
ascertained  in  the  case  of  man  and  animals  by  the  aid  of  an  apparatus,  the 
calorimeter.  An  animal  is  enclosed  in  a  metal  cage  completely  contained 
in  a  second  cage  containing  water.  Air  is  led  into  and  out  of  the  inner  box 
by  means  of  metal  tubes  so  arranged  that  the  inlet  tubes  maintain  a  con- 
stant temperature  and  the  outlet  tubes  pass  through  water  between  the  two 
chambers.  The  heat  given  out  by  the  animal  warms  the  water  in  the  outside 
box,  and  may  be  estimated  by  the  rise  of  its  temperature,  the  amount  of  which 
is  known.     At  the  same  time  the  carbon  dioxide  output  is  measured. 

The  amount  of  heat  evolved  by  the  oxidation  of  various  food  stuffs  has 
been  carefully  measured  by  numerous  observers;  the  figures  calculated  by 
Rubner  being  perhaps  most  satisfactory,  which  are: 

Heat  Value  to  the  Body. 

i  gram  carbohydrate 4.1   Calories 

1       "      fat 9-3 

1       "     proteid 4.1 

One  gram  of  dry  proteid  ha;;  a  total  heat  value  of  5.754  (Rubner),  hence 
it  is  obvious  that  proteid  is  not  completely  oxidized  by  the  body.  Each 
gram  of  proteid  yields  at  least  one-third  of  a  gram  of  urea,  which  has  a  heat 
value  of  2.5  Calories  per  gram. 

Atwater  has  checked  the  energy  value  of  the  foods  actually  consumed 
against  the  actual  liberation  of  heat  and  work  energy  of  the  human  body. 
He  finds  a  wonderfully  close  agreement  both  for  periods  of  rest  and  for  periods 
of  work.  Atwater's  estimate  for  the  energy  needs  of  man  are  summarized 
as  follows: 

Man  without  muscular  work 2,700  Calories 

"     with  light  muscular  work 3,000       " 

"        "     moderate  muscular  work 3>5°°       " 

"        "     severe  "       4>5°°       " 

The  daily  output  of  energy  for  the  adult  man  is,  according  to  McKendrick, 
as  follows: 

Kilogrammeters.     Calories. 

Work  of  heart  per  day 88,000 

Work  of  respiratory  muscle 14,000 

Eight  hours'  active  work 213,344 

3r5,334  or  743 

Amount  of  heat  produced  in  24  hours 1,582,700  or       3,724 

1,898,034  or       4,467 


THE     INFLUENCE     OF    THE     DUCTLESS    GLANDS    ON    METABOLISM    427 

This  estimate  is  relatively  high  for  ordinary  activity  as  determined  by 
Atwater  and  others.  It  is  indeed  more  energy  than  the  standard  diets  in 
the  table  given  on  page  423  will  yield  to  the  body.  For  example,  Voit's 
diet  yields  3,055  Calories,  and  the  average  of  the  table  is  only  3,125  Calories. 

THE  INFLUENCE  OF  THE  DUCTLESS  GLANDS  ON  METABOLISM. 

A  further  question  to  be  considered  is  the  relationship  between  the  metab- 
olism of  one  tissue  and  the  products  of  the  metabolism  of  other  tissues. 
The  metabolism  of  one  tissue  may  produce  products,  proteid  or  otherwise, 
which  when  taken  up  by  the  blood  and  carried  to  other  tissues  supply  ex- 
actly what  is  necessary  for  their  complete  anabolism. 

The  physiology  of  the  internal  secretions  has  revealed  a  number  of  such 
influences  that  are  best  explained  on  the  assumption  of  the  presence  of  spe- 
cial products. 

The  Thyroid.  The  thyroid  gland  is  situated  in  the  neck.  It  con- 
sists of  two  lobes,  one  on  each  side  of  the  trachea,  extending  upward  to  the 


Fig.  311. — Part  of  a  Section  of  the  Human  Thyroid,  a.  Fibrous  capsule;  b,  thyroid  vesicles 
filled  with,  e,  colloid  substances;  c,  supporting  fibrous  tissue;  d,  short  columnar  cells  lining  vesicles; 
/,  arteries;  g,  veins  filled  with  blood;  h,  lymphatic  vessel  filled  with  colloid  substance.  (S.  K. 
Alcock.) 

thyroid  cartilage,  covering  its  inferior  cornu  and  part  of  its  body;   these  lobes 
are  connected  across  the  middle  line  by  a  middle  lobe  or  isthmus.     The 


428  METABOLISM,    NUTRITION,     AND     DIET 

thyroid  is  covered  by  the  muscles  of  the  neck.  It  is  highly  vascular,  and 
varies  in  size  in  different  individuals. 

The  gland  is  encased  in  a  thin  transparent  layer  of  dense  areolar  tissue, 
free  from  fat,  containing  elastic  fibers. 

These  gland  vesicles  are  each  lined  with  a  single  layer  of  cubical  cells  and 
are  filled  with  transparent  nucleo-albuminous  colloid  material. 

Accessory  Thyroids.  The  accessory  and  the  parathyroids  possess 
the  structure  of  the  thyroid  and  apparently  perform  the  same  function.  The 
accessory  thyroids  undergo  hypertrophy  when  the  thyroid  has  been  removed. 

The  colloid  material  which  is  formed  within  the  thyroid  vesicles,  and  is 
believed  to  be  their  secretion,  finally  ruptures  through  their  walls  into  the 
lymph  channels  and  thus  gains  entrance  to  the  circulation.  The  secretion 
of  the  thyroid  falls  into  the  class  known  as  internal  secretions,  and  exerts  a 
profound  influence  upon  the  metabolic  processes  of  the  body,  probably 
through  its  influence  on  the  central  nervous  system.  Complete  extirpation 
of  the  thyroid,  at  least  in  some  animals,  produces  death,  preceded  by  a  group 
of  characteristic  symptoms.  In  man  and  the  monkey  the  symptoms  after  re- 
moval come  on  slowly  and  resemble  the  disease  known  in  man  as  myxedema. 

This  disease  is  known  definitely  to  be  due  to  disease  of  the  thyroid,  where- 
by its  function  is  interfered  with.  Moreover,  if  a  piece  of  thyroid  of  sufficient 
size  be  grafted  into  an  animal  from  which  the  glands  have  been  removed, 
and  the  graft  takes,  the  symptoms  of  thyroid  removal  are  lessened  in  inten- 
sity or  disappear  altogether.  Thyroid  feeding  or  the  administration  of 
thyroid  extracts  relieves  the  symptoms  of  the  disease  myxedema. 

The  above  facts  show  that  the  thyroid  gland  must  perform  some  im- 
portant function  in  the  animal  economy,  and  it  is  believed  that  this  is  accom- 
plished by  virtue  of  its  internal  secretion.  The  colloid  material  of  the  gland 
has  been  submitted  to  much  chemical  study,  and  a  substance  called  iodo- 
thyrin  has  been  isolated  as  its  active  principle.  Baumann  and  Roos  state 
that  iodothyrin  exists  in  the  gland  in  combination  with  proteid  bodies.  Iodo- 
thyrin  relieves  the  symptoms  of  .thyroid  removal  much  to  the  same  extent 
as  thyroid  feeding.  It  is  a  very  resistant  substance,  and  is  not  injured  by  the 
action  of  the  gastric  juice  or  by  boiling  with  10  per  cent  sulphuric  acid  for 
a  long  time. 

The  Suprarenal  Capsules  or  Adrenals.  These  are  two  flattened, 
more  or  less  triangular  or  cocked-hat  shaped  bodies,  resting  by  their  lower 
border  upon  the  upper  border  of  the  kidneys. 

The  gland  tissue  proper  consists  of  an  outside  firmer  cortical  portion,  and 
an  inside  soft  dark  medullary  portion,  figure  312. 

The  adrenals  are  very  abundantly  supplied  with  nerves,  chiefly  com- 
posed of  medullated  fibers.  These  fibers  are  derived  from  the  solar  and  renal 
plexuses  and  the  vagi,  but  the  method  of  their  termination  is  unknown. 

A  vast  amount  of  information  has  been  given  concerning  the  function  of 


THE    SUPRARENAL    CAPSULES     OR  ADRENALS 


429 


the  suprarenal  capsules  within  the  last  few  years  by  the  researches  of  Schafer 
and  Oliver,  Zyboulski,  Abel,  and  others.  Brown-Sequard,  it  is  true,  showed 
by  experiment  as  early  as  1856  that  removal  of  the  suprarenals  is  followed 
by  the  death  of  the  animal,  but  his  experiments  were  repeated  by  others  who 


Fig.  312. — Vertical  Section  of  Adrenal.     A,  Capsule;  B,  cortex;  C,  medulla;  a,  glomerular 
zone;  b,  fascicular  zone;   c,  reticular  zone;  v,  vein  in  medulla.    (Merkel-Henle.) 

did  not  obtain  the  same  results;  and  it  was  concluded  that  the  suprarenal 
capsules  had  no  function,  or  at  least  that  their  function  was  not  known. 
Death  was  preceded  in  the  case  of  Brown-Sequard's  animals  by  symptoms 
somewhat  analogous  to  those  of  the  disease  of  man  known  as  Addison's 
disease.  The  failures  to  produce  symptoms  after  attempted  removal  of  the 
glands  have  probably  resulted  from  incomplete  removal  or  the  presence  of 


430 


METABOLISM,     NUTRITION,     AND     DIET 


accessory  bodies.  Accessory  suprarenal  capsules  are  commonly  present  in 
some  animals  and  are  sometimes  found  in  man.  Further,  if  one  gland  is 
removed,  the  other  hypertrophies.  The  experiments  of  all  recent  observers 
confirm  the  original  experiments  of  Brown-Sequard.  The  presence  of  the 
suprarenal  capsules  is  essential  to  life. 

Schaffer  and  Oliver  found  that  injections  of  suprarenal  extract  produced 
marked  effects  upon  the  muscular  layer  of  the  arteries,  the  muscular  tissue 
of  the  heart,  and  the  skeletal  muscles.  The  muscular  layer  of  the  arteries 
is  markedly  contracted,  causing  vaso-constriction  and  a  rise  of  blood  pressure. 


Fig. 


313. — Injection  of  Suprarenal  Extract.     Effect  upon  the  heart,  limb,  spleen,  and  blood 
pressure,  after  section  of  cord  and  vagi.     (Reduced  to  one-half.)      (Schaffer.) 


When  the  heart  is  freed  from  nervous  control  its  contractions  are  increased 
both  in  force  and  frequency,  still  further  raising  blood  pressure.  If  the  vagi 
are  undisturbed  the  heart  beats  more  slowly,  showing  an  increase  of  vagus 
tone  due  to  stimulation  of  the  vagus  center  in  the  medulla.  The  contraction 
of  the  skeletal  muscles  in  response  to  a  single  stimulus  is  increased. 

Very  small  doses  of  suprarenal  extract  are  sufficient  to  produce  marked 
effects.  Thus  Schaffer  states  that  less  than  TTTUTTo  gram  ( TO"o  gram)  °f  tne 
desiccated  gland  is  sufficient  to  produce  an  effect  upon  the  heart  and  arter- 
ies of  an  adult  man. 

It  is  a  curious  fact  that  only  extracts  of  the  medullary  portion  of  the  gland 


THE     PITUITARY    BODY  431 

are  active.  It  has  been  further  shown,  by  Christiani  and  others,  that  if  only 
small  portions  of  the  medulla  remain,  the  animal  operated  upon  survives; 
while  if  all  the  medullary  substance  be  removed,  even  though  large  portions 
of  the  cortex  remain,  the  animal  invariably  dies. 

Abel  has  succeeded  in  separating  the  blood-pressure-raising  constituent 
of  the  extract,  and  calls  it  epinephrin,  C10H13NO3  ^H20.  Adrenalin  was 
isolated  by  Takamine  and  assigned  the  formula  C9H13N03.  The  hydro- 
chloride salt  is  prepared  commercially  and  produces  all  the  vascular  effects 
assigned  to  the  gland. 

Destruction  of  the  suprarenal  capsules  through  disease  in  man  results  in 
the  production  of  a  group  of  symptoms  known  as  Addison's  disease.  The 
administration  of  suprarenal  extract  to  these  cases  sometimes  results  bene- 
ficially, but  not  so  uniformly  as  thyroid  feeding  does  in  myxedema. 

Dreyer  has  given  evidence  that  the  products  of  this  gland  are  discharged 
into  the  blood  of  the  adrenal  vein  in  increased  quantity  on  splanchnic  stim- 
ulation. 

This  gland  furnishes,  on  the  whole,  very  conclusive  evidence  of  the  pres- 
ence of  an  internal  secretion  that  is  absolutely  necessary  to  the  normal  metab- 
olism of  other  organs. 

The  Pituitary  Body.  This  body  is  a  small  reddish-gray  mass, 
occupying  the  sella  turcica  of  the  sphenoid  bone. 

It  consists  of  two  lobes,  a  small  posterior  one  of  nervous  tissue,  and  an 
anterior  one  resembling  the  thyroid  in  structure.  The  gland  spaces  are  oval, 
nearly  round  at  the  periphery,  spherical  toward  the  center  of  the  organ,  and 
are  filled  with  nucleated  cells  of  various  sizes  and  shapes  not  unlike  gan- 
glion cells. 

The  function  of  the  pituitary  body  has  not  yet  been  fully  established. 
It  has  been  supposed  that  the  pituitary  body  has  a  function  associated  with 
that  of  the  thyroid.  On  the  other  hand,  tumors  or  other  disease  of  the  pitui- 
tary body  have  been  found  after  death  in  association  with  a  disease  known 
as  acromegaly,  in  which  the  bones  and  soft  parts  undergo  great  hvpertrophy. 
Howell  has  found  that  extracts  of  the  glandular  lobe  are  inactive,  but  that 
extracts  of  the  infundibular  lobe,  when  injected  into  the  circulation,  produce 
marked  rise  of  blood  pressure,  increase  of  vagus  tonic  inhibition,  and  an 
augmentation  of  the  heart's  force. 

The  Internal  Secretion  of  the  Pancreas.  Minkowski  and  von 
Mering  have  shown  that  total  extirpation  of  the  pancreas  is  followed  in  all 
cases  by  the  appearance  of  sugar  in  the  urine  in  the  course  of  a  few  hours. 
The  amount  of  sugar  which  appears  is  considerable,  from  5  to  10  per  cent. 
This  experimental  disease  is  accompanied  by  an  increase  in  the  quantity  of 
urine  and  by  abnormal  thirst  and  appetite,  and  proves  fatal  in  fifteen  days  or 
less.  These  results  are  obtained  only  when  the  entire  gland  or  more  than 
nine-tenths  of  it  have  been  removed.     If  one-tenth  or  more  of  the  gland  be  left 


432  METABOLISM,    NUTRITION,    AND    DIET 

behind,  sugar  appears  in  the  urine  when  carbohydrates  are  eaten,  but  not 
otherwise.  Nor  is  it  necessary  that  the  remaining  portion  of  the  gland  be  in 
its  normal  situation.  Successful  grafts  of  pancreas  under  the  skin  of  the 
abdomen  or  elsewhere  will  prevent  the  appearance  of  sugar  in  the  urine  and 
the  other  symptoms.  If,  however,  the  graft  be  subsequently  removed,  the 
sugar  in  the  urine  and  the  other  symptoms  reappear,  and  the  experimental 
disease  proceeds  to  a  rapidly  fatal  issue. 

The  symptoms  produced  by  total  extirpation  of  the  pancreas  do  not  de- 
pend upon  the  loss  of  the  pancreatic  juice  proper  to  the  organism.  This 
secretion  may  be  diverted  from  the  intestine  through  a  pancreatic  fistula 
without  the  production  of  diabetes.  Moreover,  Hedon  and  Thiroloix  have 
rendered  the  acini  of  the  gland  functionally  inactive,  and  ultimately  de- 
stroyed them,  by  the  injection  of  paraffin  or  other  substances  into  the  duct 
of  Wirsung,  without  the  supervention  of  diabetes. 

These  experiments  have  shown  that  the  ordinary  secreting  cells  degener- 
ate and  the  islands  of  Langerhans  increase  in  size,  leading  to  the  conclusion 
that  these  are  the  structures  that  produce  a  special  internal  secretion  which 
influences  or  controls  carbohydrate  metabolism  in  the  body.  Whether  this 
hypothetical  substance  is  necessary  to  the  dehydration  and  synthesis  of  dex- 
trose in  the  body  or  whether  it  is  necessary  to  the  complete  oxidation  of  carbo- 
hydrate is  at  present  a  matter  of  inference. 

The  Reproductive  Glands.  The  ovary  and  the  testes  are  un- 
doubtedly concerned  with  metabolism  in  the  body.  It  has  been  shown 
repeatedly  that  extracts  of  the  testes  when  injected  into  the  system  lead  to 
increased  vigor,  both  of  the  muscular  and  of  the  nervous  systems.  Ergograms 
show  an  increase  in  muscular  power.  Spermin  isolated  from  the  testes  is 
claimed  by  its  discoverer  to  produce  the  beneficial  effects  described.  The  re- 
moval of  the  testes  in  domestic  animals  is  followed  by  an  entire  change  in  the 
character  of  the  development  of  the  animal,  especially  in  the  so-called  second- 
ary sexual  characters.     Such  animals  show  less  vigor  and  muscular  power. 

The  removal  of  the  ovaries  in  women,  through  surgical  operation,  has 
resulted  in  very  marked  nervous  symptoms.  These  symptoms  are  reduced 
or  entirely  disappear  on  grafting  a  portion  of  the  gland,  and  the  disturbed 
menstruation  following  ovariotomy  becomes  regular  again.  Experiments  by 
Loewy  and  Richter  indicate  that  oxidations  in  the  body  are  greatly  increased 
on  feeding  ovarian  extract  to  ovariotomized  animals. 

There  are  other  organs  whose  function  is  still  obscure  but  in  which 
the  indirect  evidence  points  to  an  influence  on  metabolism  at  one  stage  or 
another  of  the  existence  of  the  animal  body.  Enough  has  been  given  here 
to  show  that  the  interrelation  of  the  organs  is  extremely  complex  in  so  far  as 
the  metabolism  is  concerned.  It  is  not  enough  simply  to  know  the  foods  and 
their  composition.  The  whole  complex  of  intermediary  metabolism  and 
their  influence  must  constantly  be  taken  into  consideration. 


CHAPTER  XII 

ANIMAL  HEAT 

Heat  is  produced  by  the  metabolism  of  the  tissues  of  the  body.  In  man 
and  in  such  animals  as  are  called  warm-blooded,  i.e.,  only  mammals  and 
birds,  there  is  an  average  body  temperature  which  is  maintained  with  only 
slight  variations  in  spite  of  changes  in  their  environment.  The  possible 
variations  above  and  below  this  average  are  comparatively  slight.  The 
average  temperature  in  all  mammals  and  birds  is  not  the  same,  for,  as  we 
shall  see,  the  average  temperature  of  man  is  370  C.  (98. 6°  F.),  in  some  birds 
it  is  as  high  as  440  C,  while  in  the  wolf  it  is  said  to  be  under  360  C. 

The  average  temperature  of  the  human  body  in  those  internal  parts  which 
are  most  easily  accessible,  as  the  mouth  and  rectum,  is  from  36. 90  to  37. 40  C. 
(98. 50  to  99. 5°  F.).  In  different  parts  of  the  external  surface  of  the  human 
body  the  temperature  varies  only  to  the  extent  of  one  or  two  degrees  centi- 
grade, when  all  are  alike  protected  from  cooling  influences;  and  the  differ- 
ence which  under  these  circumstances  exists  depends  chiefly  upon  the 
different  degrees  of  blood  supply.  In  the  axilla  and  in  the  groin,  the  most 
convenient  situations,  under  ordinary  circumstances,  for  examination  by  the 
thermometer,  the  average  temperature  is  370  C.  (98. 6°  F.).  In  different 
internal  parts,  the  variation  is  one  or  two  degrees;  those  parts  and  organs 
being  warmest  which  contain  most  blood,  and  in  which  there  occurs  the 
greatest  amount  of  chemical  change,  e.g.,  the  muscles  and  the  glands.  The 
temperature  is  highest  when  they  are  in  a  condition  of  activity.  Those  tis- 
sues which  subserve  only  a  mechanical  function  and  are  the  seat  of  least  ac- 
tive circulation  and  chemical  change  are  the  coolest.  These  differences  of 
temperature,  however,  are  actually  but  slight,  on  account  of  the  provisions 
which  exist  for  maintaining  uniformity  of  temperature  in  different  parts. 

The  average  temperature  of  a  healthy  body  varies  somewhat  according 
to  age,  sex,  time  of  day,  climate,  etc.  The  mean  temperature  is  said  to  be 
slightly  higher,  0.50  C,  in  young  children  and  in  old  persons  than  in  adults. 
It  is  perhaps  very  slightly  higher  in  women  than  in  men,  in  warm  climates 
than  in  cold,  in  winter  than  in  summer.  It  varies  slightly  at  different  times 
in  the  day,  especially  during  sleep  when  metabolism  is  at  a  low  ebb. 

Heat-producing  Organs.  Heat  is  liberated  in  the  body  wherever 
oxidative  metabolism  takes  place.  Of  all  the  tissues  of  the  body  muscular 
tissue  is  conspicuous  for  its  mass  and  for  its  activity.  It  is  evidently  the  great 
28  433 


434  ANIMAL    HEAT 

heat-producing  tissue.  The  manifestation  of  muscular  energy  is  always  ac- 
companied by  the  evolution  of  heat  and  the  production  of  carbon  dioxide. 
This  production  of  carbon  dioxide  goes  on  while  the  muscles  are  in  mechanical 
rest,  only  in  a  less  degree  than  that  which  is  noticed  during  muscular  activity, 
and  so  it  is  certain  that  an  active  catabolism  is  going  on  in  resting  as  well  as 
in  contracting  muscles.  This  catabolism  is  a  source  of  much  heat,  and  so 
the  total  amount  of  heat  produced  in  the  muscular  tissues  per  day  must  be 
very  great.  It  has  been  calculated  that,  even  neglecting  the  heat  produced 
by  the  quiet  catabolism  of  muscular  tissue,  the  amount  of  heat  generated  by 
muscular  activity  would  supply  the  principal  part  of  the  total  heat  produced 
within  the  body.  The  heart,  as  a  special  muscle,  deserves  particular  mention 
since  it  is  in  constant  vigorous  activity.  All  its  energy  is  ultimately  converted 
into  heat,  accounting  for  about  5  per  cent  of  the  total  heat  of  the  body.  The 
secreting  glands,  and  principally  the  liver  as  being  the  largest  and  most  ac- 
tive, come  next  to  the  muscles  and  heart  as  heat-producing  tissues.  It  has 
been  found  by  experiment  that  the  blood  leaving  the  glands  is  considerably 
warmer  than  that  entering  them.  The  metabolism  in  the  glands  is  very 
active;   and  the  more  active  the  catabolism,  the  greater  the  heat  produced. 

It  must  be  remembered,  however,  that  although  the  organs  mentioned  are 
the  chief  heat-producing  parts  of  the  body,  all  living  tissues  contribute  their 
quota,  and  this  in  direct  proportion  to  their  activity.  The  blood  itself  is  also 
the  seat  of  catabolism,  and,  therefore,  of  the  production  of  heat;  but  the 
share  which  it  takes  in  this  respect,  apart  from  the  tissues  in  which  it  circu- 
lates, is  very  inconsiderable. 

Regulation  of  the  Temperature  of  the  Human  Body.  The  average 
temperature  of  the  body  is  maintained  under  different  conditions  of  external 
circumstance  by  mechanisms  which  permit  of  (1)  variation  in  the  loss  of  heat, 
and  (2)  variations  in  the  production  of  heat.  In  healthy  warm-blooded  ani- 
mals the  loss  and  gain  of  heat  are  so  nearly  balanced  one  by  the  other  that, 
under  all  ordinary  circumstances,  a  uniform  temperature,  within  a  degree  or 
two,  is  preserved. 

Variation  in  the  Loss  of  Heat.  The  loss  of  heat  from  the  human 
body  is  principally  regulated  by  the  amount  given  off  by  radiation  and  con- 
duction from  its  surface,  by  means  of  the  constant  evaporation  of  water  from 
the  same  part,  heat  being  thus  rendered  latent,  and  to  a  much  less  degree  by 
loss  from  the  air-passages.  In  each  act  of  respiration,  heat  is  lost  to  a  greater 
or  less  extent  according  to  the  temperature  of  the  atmosphere;  unless  indeed 
the  temperature  of  the  surrounding  air  exceeds  that  of  the  blood.  We  must 
remember,  too,  that  all  food  and  drink  which  enter  the  body  at  a  lower  tem- 
perature abstract  a  small  measure  of  heat;  while  the  urine  and  feces  which 
leave  the  body  at  about  its  own  temperature  are  also  means  by  which  a  certain 
small  amount  of  heat  is  lost. 

Heat  Lost  from  the  Surface  of  the  Body.     By  far  the  most  impor- 


HEAT     LOST     FROM    THE     SURFACE     OF    THE     BODY  435 

tant  loss  of  heat  from  the  body,  probably  90  per  cent  and  upward  of  the  whole 
amount,  is  that  which  takes  place  by  radiation,  conduction,  and  the  evapora- 
tion of  moisture  from  the  skin.  The  actual  figures  are  as  follows:  For  every 
100  calories  of  heat  produced,  2.6  are  lost  in  heating  the  food  and  drink;  2.6 
in  heating  the  air  inspired;  14.7  in  evaporation;  and  80.1  by  radiation  and 
conduction.  The  means  by  which  the  skin  is  able  to  act  as  one  of  the  most 
important  organs  for  regulating  the  temperature  of  the  blood,  are,  1,  that 
it  offers  a  large  surface  for  radiation,  conduction,  and  evaporation;  2,  that  it 
contains  a  large  but  adjustable  amount  of  blood,  and  the  quantity  of  blood 
is  greater  under  those  circumstances  which  demand  a  loss  of  heat  from  the 
body,  and  vice  versa  ;  3,  that  it  contains  the  sweat  glands,  which  discharge  a 
quantity  of  moisture  to  be  evaporated  from  its  surface. 

The  circumstance  which  directly  determines  the  quantity  of  blood  in  the 
skin  is  that  which  governs  the  supply  of  blood  to  all  the  tissues  and  organs 
of  the  body,  namely,  the  power  of  the  vaso-motor  nerves  to  cause  a  greater 
or  less  tension  of  the  muscular  element  in  the  walls  of  the  arteries,  and,  in 
correspondence  with  this,  a  lessening  or  increase  of  the  caliber  of  the  vessel, 
accompanied  by  a  less  or  greater  current  of  blood.  A  warm  or  hot  atmos- 
phere so  acts  on  the  sensory  nerves  of  the  skin  as  to  lead  them  reflexly  to 
cause  a  relaxation  of  the  muscular  fiber  of  the  blood-vessels;  as  a  result, 
the  skin  becomes  full-blooded,  relatively  hot,  and  moist  from  sweating;  and 
much  heat  is  lost.  With  a  low  temperature,  on  the  other  hand,  the  blood- 
vessels shrink,  and  with  the  consequently  diminished  blood  supply,  the  skin 
becomes  pale,  cold,  and  dry,  an  effect  produced  through  the  vascular  centers 
in  the  medulla  and  spinal  cord. 

The  activity  of  the  sweat  glands  of  the  skin  is  also  regulated  reflexly 
through  the  sweat  centers.  The  increased  blood  supply  just  described  is 
favorable  to  increased  production  of  sweat  by  the  sweat  glands.  Thus, 
by  means  of  the  self-regulation  the  skin  becomes  the  most  important  of  the 
means  by  which  the  temperature  of  the  body  is  regulated. 

The  relative  loss  of  heat  by  the  means  given,  i.e.,  radiation,  conduction, 
and  evaporation,  will  depend  on  two  factors:  first,  the  relative  temperature 
of  the  body  to  the  surrounding  air ;  and,  second,  the  humidity  of  the  air.  If  the 
atmospheric  temperature  is  the  same  as  that  of  the  body,  of  course  there  will 
be  no  loss  of  heat  by  radiation  and  convection;  if  the  air  temperature  is 
higher,  there  will  be  an  actual  gain.  When  the  humidity  of  the  air  is  great, 
there  will  be  reduced  evaporation  of  perspiration  and  consequent  diminished 
heat  loss  by  this  means.  If  we  assume  a  moisture-saturated  air  at  the  body 
temperature,  then  heat  loss  becomes  impossible  and  the  temperature  of  the 
body  will  rise.  This  is  why  a  hot  moist  climate  is  so  oppressive,  while  a 
hot  but  dry  atmosphere  is  readily  borne  by  the  human  body.  The  increased 
evaporation  of  perspiration  compensates  for  the  decreased  loss  by  radiation 
and  convection. 


436  ANIMAL    HEAT 

Many  examples  may  be  given  of  the  power  which  the  body  possesses  of  resisting  the 
effects  of  a  high  temperature,  in  virtue  of  evaporation  from  the  skin.  Blagden  and  others 
supported  a  temperature  varying  between  92°  to  ioo°  C.  (ia80-2i2°  F.)  in  dry  air  for  sev- 
eral minutes;  and  in  a  subsequent  experiment  he  remained  eight  minutes  in  a  temperature 
of  i26.5°C.  (2600  F. ).  "  The  workmen  of  SirF.  Chantrey  were  accustomed  to  enter  a  furnace, 
in  which  his  molds  were  dried,  while  the  floor  was  red-hot,  and  a  thermometer  in  the 
air  stood  at  177-8°  C.  (350°  F.),  and  Chabert,  the  fire-king,  was  in  the  habit  of  entering 
an  oven  the  temperature  of  which  was  from  205°-3i5°  C.  (40o°-6oo°  F.)."     (Carpenter.) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot,  so  as  to  prevent 
evaporation  from  the  body.  C.  James  states  that  in  the  vapor  baths  of  Nero  he  was  al- 
most suffocated  in  a  temperature  of  44. 50  C.  (112°  F.),  while  in  the  caves  of  Testaccio,  in 
which  the  air  is  dry,  he  was  but  little  incommoded  by  a  temperature  of  8o°  C.  (176°  F.). 
In  the  former,  evaporation  from  the  skin  was  impossible;  in  the  latter  it  was  abundant, 
and  the  layer  of  vapor  which  would  rise  from  all  the  surface  of  the  body  would,  by  its  very 
slowly  conducting  power,  defend  it  for  a  time  from  the  full  action  of  the  external  heat. 

Man  is  able  by  suitable  clothing  to  increase  or  to  diminish  the  amount  of 
heat  lost  by  the  skin.  There  are  baths  and  other  means  which  man  and 
animals  instinctively  adopt  for  lowering  the  temperature  when  necessary. 

Although  under  any  ordinary  circumstances  the  external  application  of  cold  only 
temporarily  depresses  the  temperature  to  a  slight  extent,  it  is  otherwise  in  cases  of  high 
temperature  in  fever.  In  these  cases  a  cool  bath  may  reduce  the  temperature  several 
degrees,  and  the  effect  so  produced  lasts  in  some  cases  for  many  hours. 

Extreme  heat  and  cold  produces  effects  too  powerful,  either  in  raising  or 
lowering  the  heat  of  the  body,  to  be  controlled  by  the  proper  regulating  ap- 
paratus. Walther  found  that  rabbits  and  dogs  kept  exposed  to  a  hot  sun, 
reached  a  temperature  of  460  C.  (114. 8°  F.),  and  then  died.  Cases  of  sun- 
stroke furnish  us  with  several  examples  in  the  case  of  man;  for  it  would  seem 
that  here  death  ensues  chiefly  or  solely  from  elevation  of  the  temperature. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less  well  known 
than  the  effect  of  heat.  From  experiments  by  Walther  it  appears  that  rab- 
bits can  be  cooled  down  to  8.90  C.  (480  F.)  before  they  die,  if  artificial  respira- 
tion be  kept  up.  Cooled  down  to  17. 8°  C.  (640  F.),  they  cannot  recover 
unless  external  warmth  be  applied  together  with  the  employment  of  artificial 
respiration.  Rabbits  not  cooled  below  250  C.  (770  F.)  recover  by  external 
warmth  alone. 

Loss  of  Heat  from  the  Lungs.  The  lungs  and  air-passages  are 
very  inferior  to  the  skin  as  a  means  for  lowering  the  temperature.  In  giving 
heat  to  the  air  breathed,  the  lungs  stand  next  to  the  skin  in  importance.  As 
a  regulating  power,  the  inferiority  is  very  marked.  The  air  which  is  ex- 
pelled from  the  lungs  leaves  the  body  at  about  the  temperature  of  the  blood, 
and  is  always  saturated  with  moisture.  No  inverse  proportion,  therefore, 
exists,  as  in  the  case  of  the  skin,  between  the  loss  of  heat  by  radiation  and 
conduction,  on  the  one  hand,  and  by  evaporation,  on  the  other.  The  colder 
the  air  and  the  drier,  for  example,  the  greater  will  be  the  loss  in  all  ways. 
Neither  is  the  quantity  of  blood  which  is  exposed  to  the  cooling  influence  of 


VARIATION     IN    THE     PRODUCTION    OF    HEAT  437 

the  air  diminished  or  increased  in  the  lungs,  so  far  as  is  known,  in  accordance 
with  any  need  in  relation  to  temperature.  It  is  true  that  by  varying  the 
number  and  depth  of  the  respirations,  the  quantity  of  heat  given  off  by  the 
lungs  may  be  made  to  vary  also  for  a  few  minutes.  But  the  respiratory 
passages,  while  they  must  be  considered  important  means  by  which  heat  is 
lost,  are  altogether  subordinate,  in  the  power  of  actively  regulating  the  tem- 
perature. 

The  loss  of  heat  used  to  warm  foods  is  an  obvious  method  of  expenditure 
of  heat  which  may  be  resorted  to,  especially  in  certain  fevers.  The  loss  of 
heat  by  the  excreta  discharged  from  the  body  at  a  high  temperature  must  be 
of  little  use  as  a  means  of  regulating  the  temperature,  since  the  amount  so 
lost  must  be  capable  of  little  variation. 

Variation  in  the  Production  of  Heat.  It  may  seem  to  have  been 
assumed,  in  the  foregoing  pages,  that  the  only  regulating  apparatus  for  tem- 
perature required  by  the  human  body  is  one  that  shall,  more  or  less,  produce 
a  cooling  effect;  as  if  the  amount  of  heat  produced  were  always,  there- 
fore, in  excess  of  that  which  is  required.  Such  an  assumption  would  be  in- 
correct. The  body  has  the  power  of  regulating  the  production  of  heat,  as 
well  as  its  loss. 

The  production  of  heat  in  the  body  is  apparently  different  for  each  ani- 
mal; i.e.,  the  absolute  amount  of  heat  set  free  by  different  animals  in  a  given 
period  varies.  Each  individual  has  his  own  coefficient  of  heat  production. 
From  all  that  has  been  said  on  the  subject  it  will  be  seen  that  the  amount  of 
heat  for  all  practical  purposes  depends  upon  the  metabolism  of  the  tissues  of 
the  body ;  everything,  therefore,  which  increases  that  metabolism  will  increase 
the  heat  production;  so,  therefore,  the  absolute  amount  of  heat  produced  by  a 
large  animal,  having  a  larger  amount  of  tissues  in  which  metabolism  may 
go  on,  will  be,  ceteris  paribus,  greater  than  that  of  a  small  animal.  But  the 
activity  of  the  tissue  change  in  a  small  animal  may  be  greater  than  in  a  large 
one,  as  measured  per  kilo  of  body-weight,  and  naturally  no  strict  line  can  be 
drawn  between  the  two. 

Heat  Produced  per  Kilo  per  Hour.     (Munk.) 

Man i-5    calories 

Dog  (large) i-7 

Dog  (small) 3-8 

Guinea-pig 7-5 

Rat ii. 3 

Mouse io- o         " 

Sparrow 35-5 

The  ingestion  of  foods  increases  the  metabolism  of  the  tissues.  As  one 
would  expect,  the  rate  of  heat  production  is  found  by  experiment  upon  the 
dog  to  be  increased  after  a  meal,  reaching  its  height  about  six  hours  after 
a  meal. 


438  ANIMAL     HEAT 

It  has  also  been  experimentally  ascertained  that  the  rate  of  heat  produc- 
tion varies  with  the  kind  of  food  taken:  for  example,  if  sugar  be  added  to  the 
meal  of  meat  given  to  the  dog,  the  height  of  maximum  production  is  reached. 
It  is  often  said  that  the  various  nations  have  found  by  experience  what  food 
is  most  suitable  for  the  climate  in  which  they  live,  and  that  such  experience 
can  be  trusted  to  regulate  the  quantity  consumed.  Although  there  have 
been  no  very  conclusive  experiments  to  prove  the  view,  yet  it  is  a  matter  of 
general  observation  that  in  northern  climates  and  in  colder  seasons  the  quan- 
tity of  food  taken  is  greater  than  in  warmer  climates  or  in  warmer  seasons. 
Moreover,  the  kind  of  food  is  different.  For  example,  persons  living  in  the 
colder  climates  require  much  fat  in  order  to  produce  the  requisite  amount 
of  heat. 

Influence  of  the  Nervous  System  on  Heat  Production.  The  in- 
fluence of  the  nervous  system  in  modifying  the  production  of  heat  must  be 
very  important,  as  upon  the  nervous  influence  depends  the  amount  of  the  metab- 
olism of  the  tissues.  The  experiments  and  observations  which  best  illus- 
trate it  are  those  showing,  first,  that,  when  the  supply  of  nerves  to  a  part  is 
cut  off,  the  temperature  of  that  part  falls  below  its  ordinary  degree  after  a 
time;  and,  second,  that  when  there  is  severe  injury  to  or  removal  of  the 
nervous  centers  the  temperature  of  the  body  rapidly  falls,  even  though  arti- 
ficial respiration  be  performed,  the  circulation  maintained,  and  to  all  appear- 
ance the  ordinary  conditions  for  chemical  changes  in  the  body  be  com- 
pletely maintained. 

There  is  a  heat-regulating  nervous  apparatus  closely  comparable  to  that 
which  regulates  the  secretion  of  saliva  or  of  sweat,  by  means  of  which  the  pro- 
duction of  heat  in  the  warm-blooded  animals  is  increased  or  diminished,  as 
occasion  requires.  This  apparatus  probably  consists  of  a  center  or  centers 
in  the  brain  which  may  be  reflexly  stimulated,  as,  for  example,  by  impulses 
from  the  skin,  and  which  act  through  special  nerves  supplied  to  the  various 
tissues.  The  evidence  upon  which  the  existence  of  this  regulating  appara- 
tus depends  is  the  marked  effect  in  the  increase  of  the  oxygen  consumed  by 
a  warm-blooded  animal  when  exposed  to  cold,  and  the  corresponding  increase 
in  the  output  of  carbon  dioxide,  indicating  that  there  is  an  increase  of  the 
metabolism  and  so  an  increased  production  of  heat  under  such  circumstances, 
and  not  a  mere  diminution  of  the  amount  of  heat  lost  by  the  skin,  etc.  A 
cold-blooded  animal  reacts  very  differently  to  exposure  to  cold;  instead  of 
increasing  the  metabolism  as  in  the  case  of  the  warm-blooded  animal,  cold 
diminishes  the  metabolism  of  its  tissues.  It  is  clear,  therefore,  that  in  warm- 
blooded animals  there  is  some  apparatus  not  possessed  by  cold-blooded  ani- 
mals, which  counteracts  the  effects  of  cold.  In  warm-blooded  animals  poi- 
soned bycurara,  or  in  which  section  of  the  medulla  has  been  done,  it  has  been 
found  that  this  regulating  apparatus  is  no  longer  in  action,  and  under  such 
circumstances  no  difference  appears  to  exist  between  such  animals  and  those 


INFLUENCE     OF     NERVOUS    SYSTEM    ON     HEAT     PRODUCTION  439 

which  are  naturally  cold-blooded.  Warmth  increases  their  temperature, 
and  cold  lowers  it,  and  with  this  there  is,  of  course,  evidence  of  diminished 
metabolism. 

The  explanation  of  these  experiments  is  that  in  such  animals  the  connec- 
tion between  the  skin  and  the  muscles  through  the  nervous  chain,  such  as 
a  thermotaxic  nervous  apparatus  might  be  supposed  to  afford,  is  broken 
either  at  the  termination  of  the  nerves  in  the  muscles  (curara)  or  at  the  sec- 
tioned point  of  the  bulb. 

The  position  of  these  hypothetical  centers  is  a  matter  of  some  difference 
of  opinion.  It  has  been  demonstrated  that  stimulation  of  certain  parts  of 
the  brain  may,  among  other  symptoms,  produce  increased  metabolism  of  the 
tissues  with  increased  output  of  carbon  dioxide  and  a  raised  temperature: 
the  parts  of  which  this  may  be  asserted  are  parts  of  the  corpus  striatum  and 
of  the  optic  thalamus.  The  general  thermogenic  centers  are  probably  closely 
associated  with  the  motor  centers  of  the  cord  and  brain  stem.  The  thermo- 
regulative  centers  are  the  nuclei  in  the  corpus  striatum  and  optic  thalamus. 
Assuming  a  constant  or  tonic  activity  of  the  thermogenic  regulative  centers, 
it  is  easy  to  understand  the  fall  of  temperature  on  their  destruction  or  on  the 
destruction  of  the  nerve  path  to  the  active  tissues. 

Experimental  observations,  such  as  have  been  made  upon  animals,  receive 
confirmation  from  the  observations  on  patients  who  suffer  from  fever  or 
pyrexia;  in  them  the  temperature  of  the  body  may  be  raised  several  de- 
grees, as  we  have  already  pointed  out.  This  increase  of  temperature 
might,  of  course,  be  due  to  diminished  loss  of  heat  from  the  skin,  but  this, 
although  a  factor,  is  not  the  only  cause.  The  amount  of  oxygen  taken  in 
and  the  amount  of  carbon  dioxide  given  out  are  both  increased,  and  with 
this  there  must  be  increased  metabolism  of  the  tissues,  and  particularly  of 
the  muscular  tissues,  since  at  the  same  time  the  amount  of  urea  in  the  urine 
is  increased.  Every  one  is  familiar  with  the  rapid  wasting  which  is  such  a 
characteristic  of  high  fever;  it  must  indicate  not  only  too  rapid  metabolism 
of  the  body,  but  also  insufficient  time  for  the  tissues  to  build  themselves  up. 
In  fever,  then,  there  may  be  supposed  to  be  some  interference  with  the  ordinary 
reflex  channel  by  which  the  skin  is  able  to  communicate  to  the  nervous  sys- 
tem the  necessity  of  an  increased  or  diminished  production  of  heat  in  the 
muscles  and  other  tissues.  In  consequence  of  this,  and  in  spite  of  the  con- 
dition of  increased  heat  of  the  body,  both  at  the  surface  and  in  the  deeper 
tissues,  the  production  of  heat  goes  on  at  an  abnormal  rate.  It  is  not  certain 
whether  the  pathological  condition  is  one  which  stimulates  the  thermogenic 
center  by  means  of  which  the  metabolism  of  the  tissues  is  increased,  or  whether 
the  normal  reflexes  which  ordinarily  inhibit  the  activity  of  the  center  when 
the  temperature  rises  fail  to  bring  about  their  usual  reaction.  The  first  is 
the  probable  explanation  of  the  high  fevers  of  certain  toxemias. 


CHAPTER  XIII 

MUSCLE-NERVE  PHYSIOLOGY 
CHEMICAL   COMPOSITION   OF   MUSCLE 

Muscle  Plasma.  The  principal  substance  which  can  be  extracted 
from  muscle,  when  examined  after  death,  is  the  proteid  body,  myosin,  some 
of  the  reactions  of  which  have  been  already  discussed.  This  body  appears  to 
bear  somewhat  the  same  relation  to  the  living  muscle  that  fibrin  does  to 
the  living  blood,  since  the  coagulation  of  muscle  after  death  is  due  to  the 
formation  of  myosin.  Thus,  if  coagulation  be  delayed  by  removing  the 
muscles  immediately  that  an  animal  is  killed,  and  rapidly  cooling  them  to  a 
temperature  below  o°  C.  before  the  muscles  themselves  lose  their  irritability, 
it  is  possible  to  express  from  them  a  viscid  fluid  of  slightly  alkaline  reaction, 
called  muscle  plasma  (Kiihne,  Halliburton).  Muscle  plasma,  if  exposed  to 
the  ordinary  temperature  of  the  air  (or  more  quickly  at  370  to4o°C),  undergoes 
coagulation  much  in  the  same  way  as  does  blood  plasma  under  similar  cir- 
cumstances when  separated  from  the  blood-corpuscles  at  a  low  temperature. 
The  appearances  presented  by  the  fluid  during  the  process  are  also  very 
similar  to  the  phenomena  of  blood-clotting,  viz.,  first  of  all  an  increased 
viscidity  appears  on  the  surface  of  the  fluid,  and  at  the  sides  of  the  containing 
vessel,  which  gradually  extends  throughout  the  entire  mass,  until  a  fint 
transparent  clot  is  obtained.  In  the  course  of  some  hours  the  clot  begins 
to  contract,  and  to  squeeze  out  of  its  meshes  a  fluid  corresponding  to  blood 
serum.  In  the  course  of  coagulation,  therefore,  muscle  plasma  separates 
into  muscle  clot  and  muscle  serum.  The  muscle  clot  contains  the  substance 
myosin.  It  differs  from  fibrin  in  being  easily  soluble  in  a  2  per  cent  solution 
of  hydrochloric  acid,  and  in  a  10  per  cent  solution  of  sodium  chloride.  It  is 
insoluble  in  distilled  water,  and  its  solutions  coagulate  on  application  of  heat; 
in  short,  it  is  a  globulin.  During  the  process  of  clotting  the  reaction  of  the 
fluid  becomes  distinctly  acid. 

The  coagulation  of  muscle  plasma  can  be  prevented  not  only  by  cold, 
but  also,  as  Halliburton  has  shown,  by  the  presence  of  neutral  salts  in  certain 
proportions;  for  example,  of  sodium  chloride,  magnesium  sulphate,  or  sodium 
sulphate.  It  will  be  remembered  that  this  is  also  the  case  with  blood  plasma. 
Dilution  of  the  salted  muscle  plasma  will  produce  its  slow  coagulation,  which 
is  prevented  by  the  presence  of  the  neutral  salts  in  strong  solution. 

440 


MUSCLE    SERUM  441 

It  is  highly  probable  that  the  formation  of  muscle  clot  is  due  to  the  presence 
of  a  ferment,  myosin  ferment.  The  antecedent  myosin  in  living  muscle  has 
received  the  name  of  myosinogen,  in  the  same  way  that  the  fibrin-forming 
element  in  the  blood  is  called  fibrinogen.  Myosinogen  is,  however,  a  mixture 
of  two  globulins  which  coagulate  at  the  temperatures  470  C.  and  560  C.  re- 
spectively. 

Myosin  may  also  be  obtained  from  dead  muscle  after  all  the  blood,  fat,  and 
fibrous  tissue,  and  substances  soluble  in  water  have  been  removed  by  subjecting 
it  to  a  10  per  cent  solution  of  sodium  chloride,  or  a  5  per  cent  solution  of  mag- 
nesium sulphate,  or  a  10  to  15  per  cent  solution  of  ammonium  chloride, 
filtering  and  allowing  the  filtrate  to  drop  into  a  large  quantity  of  water.  The 
myosin  separates  out  as  a  white  flocculent  precipitate.  The  precipitate  gives 
all  the  globulin  reactions. 

Muscle  Serum.  Muscle  serum  is  acid  in  reaction,  and  almost  col- 
orless. It  contains  three  proteid  bodies,  viz. :  A  globulin  (my 0 globulin), 
which  can  be  precipitated  by  saturation  with  sodium  chloride,  or  magnesium 
sulphate,  and  which  can  be  coagulated  at  630  C. ;  serum  albumin  (myo- 
albitmin),  which  coagulates  at  730  C,  but  is  not  precipitated  by  saturation 
with  either  of  those  salts;  and  myo-albumose,  which  is  neither  precipitated  by 
heat  nor  by  saturation  with  sodium  chloride  or  magnesium  sulphate,  but 
may  be  precipitated  by  saturation  with  ammonium  sulphate.  It  is  closely 
connected  with,  even  if  it  is  not  itself,  myosin  ferment.  Neither  casein  nor 
peptone  has  been  found  by  Halliburton  in  muscle  extracts.  In  extracts  of 
muscles,  especially  of  red  muscles,  there  is  a  certain  amount  of  hemoglobin, 
and  also  of  a  pigment'  special  to  muscle,  called  by  McMunn  myo-hematin, 
which  has  a  spectrum  quite  distinct  from  hemoglobin,  viz.,  a  narrow  band 
just  before  D,  two  very  narrow  bands  between  D  and  E,  and  two  other  faint 
bands,  near  E  b,  and  between  E  and  F  close  to  F. 

Other  Constituents  of  Muscle.  In  addition  to  muscle  ferments, 
already  mentioned,  muscle  extracts  contain  certain  small  amounts  of  pepsin 
and  fibrin  ferment  and  an  amylolytic  ferment. 

Certain  acids  are  also  present,  particularly  sarco-lactic,  as  well  as  traces  of 
acetic  and  formic. 

Of  carbohydrates,  glycogen  and  glucose  (or  maltose)  and  inosite  are 
present.  Glycogen  is  present  in  considerable  amount,  especially  in  the 
muscles  of  well-nourished  young  animals.  The  glycogen  is  converted  to  mal- 
tose in  the  muscles  on  standing  some  hours  after  death. 

Nitrogenous  crystalline  bodies,  such  as  creatin,  creatinin,  xanthin,  hypo- 
xia; tli in,  or  carnin,  taurin,  urea  in  very  small  amount,  uric  acid,  and  inosinic 
acid,  are  all  found  on  extracting  dead  muscle. 

Salts  of  potassium  and  calcium  are  present  in  muscle,  the  chief  of  which 
is  potassium  phosphate. 


442  MUSCLE-NERVE     PHYSIOLOGY 

THE    PROPERTIES   OF   LIVING   MUSCLE. 

Elasticity.  Muscle  has  a  certain  amount  of  elasticity  during  rest. 
It  admits  of  being  considerably  stretched,  but  returns  readily  and  completely 
to  its  normal  condition.  In  the  living  body  the  muscles  are  always  stretched 
somewhat  beyond  their  natural  length,  they  are  always  in  a  condition  of 
slight  tension;  an  arrangement  which  enables  the  whole  force  of  the  con- 
traction to  be  utilized  in  approximating  the  points  of  attachment.  If  the  ex- 
tensibility of  a  given  muscle  be  measured  by  adding  to  it  equal  increments 
of  weight,  it  will  be  found  that  the  extension  or  stretching  is  considerable  at 
first,  but  that  the  amount  decreases  with  each  additional  weight.  If  the 
figures  obtained  be  plotted  on  coordinate  paper,  a  curve  approaching  a  parab- 
ola is  obtained,  whereas  a  steel  spring  is  perfectly  elastic  and  gives  a  straight 
line.  When  the  weights  are  removed  from  a  stretched  muscle,  one  by  one, 
the  muscle  regains  its  original  length,  though  slowly.  Extreme  fatigue 
greatly  decreases  the  elasticity,  while  an  increase  of  temperature  increases  it. 

Cardiac  muscle  and  smooth  muscle  both  manifest  elasticity  in  the  same 
manner  as  skeletal  muscle.  In  fact  the  elasticity  of  the  arterioles  is  chiefly 
due  to  the  smooth  muscle  in  their  walls,  a  fact  that  is  of  great  importance  in  the 
adaptability  of  the  circulatory  apparatus.  The  flexibility  of  the  stomach, 
the  urinary  bladder,  etc.,  is  traceable  to  the  same  property  of  their  muscular 
walls. 

Contractility  and  Irritability  of  Muscle.  The  property  of  muscular 
tissue  by  which  its  peculiar  functions  are  exercised  is  its  contractility,  which 
is  excited  by  all  kinds  of  stimuli  applied  either  directly  to  the  muscles  or  in- 
directly to  them  through  the  medium  of  their  motor  nerves.  The  property 
of  the  muscle  which  enables  it  to  respond  to  a  stimulus  is  called  its  irritability. 
This  property,  although  commonly  brought  into  action  through  the  nervous 
system,  is  inherent  in  the  muscular  tissue.  This  is  proven:  i,  By  the  fact 
that  contractility  is  manifested  in  a  muscle  which  is  isolated  from  the  influence 
of  the  nervous  system  by  division  of  the  nerves  supplying  it  so  long  as  the  natu- 
ral tissue  of  the  muscle  is  duly  nourished.  2,  It  is  manifested  in  a  portion  of 
muscular  fiber  in  which,  under  the  microscope,  no  nerve  fiber  can  be  traced. 
3,  Substances  such  as  curara,  which  paralyze  the  nerve  endings  in  muscles, 
do  not  at  a-1  diminish  the  irritability  of  the  muscle  itself.  4,  When  a  muscle 
is  fatigued,  a  local  stimulation  is  followed  by  a  contraction  of  a  small  part  of 
the  fiber  in  the  immediate  vicinity,  without  any  regard  to  the  distribution  of 
nerve  fibers. 

Forms  of  Stimuli  for  Muscle  or  Nerve.  The  power  of  contraction 
in  voluntary  muscles  is  normally  called  forth  in  the  body  by  nerve  impulses 
which  reach  the  muscles  over  the  motor  nerves.  But  a  muscle  will  respond 
to  stimuli  of  various  kinds,  and  these  stimuli  may  be  applied  directly  to  the 
muscle  or  indirectly  to  the  nerve  supplying  it.     There  are  distinct  advantages, 


FORMS     OF     STIMULI     FOR     MUSCLE     OR     NERVE 


443 


however,  in  applying  the  stimulus  to  the  nerve,  as  it  is  more  convenient,  as 
well  as  more  potent.  The  stimuli  which  will  produce  contraction  in  a  muscle 
are: 

1.  Mechanical  Stimuli.  A  blow,  pinch,  prick,  of  the  muscle  or  its  nerve 
will  produce  a  contraction,  repeated  on  the  repetition  of  the  stimulus.  If 
applied  to  the  same  point  for  a  number  of  times  such  stimuli  will  soon  destroy 
the  irritability  of  the  preparation. 

2.  Thermal  Stimuli.  If  a  needle  or  glass  rod  be  heated  and  applied  to  a 
muscle  or  its  nerve,  the  muscle  will  contract.  A  temperature  of  over  450  C. 
will  cause  the  muscles  of  a  frog  to  pass  into  a  condition  known  as  heat  rigor. 
The  sudden  change  of  temperature  acts  as  a  stimulus. 

3.  Chemical  Stimuli.  A  great  variety  of  chemical  substances  will  excite 
the  contraction  of  muscles,  some  substances  being  more  potent  in  irritating 
the  muscle  itself,  and  other  substances  having  more  effect  upon  the  nerve. 
Of  the  former  may  be  mentioned  dilute  acids,  salts  of  certain  metals,  e.g., 
zinc,  copper,  and  iron;  to  the  latter  belong  strong  glycerin,  strong  acids, 
ammonia,  bile  salts  in  strong  solution,  etc. 

4.  Electrical  Stimuli.  Any  form  of  electrical  current  may  be  employed 
to  stimulate  a  muscle  to  contract,  but  either  galvanism  or  the  induced  current 
is  usually  chosen.  For  experimental  purposes  electrical  stimuli  are  most 
frequently  used,  as  the  strength  of  the  stimulus  may  be  conveniently  regulated. 
In  order  that  a  stimulus  shall  be  effective,  it  must  have  a  certain  amount  of 
energy  and  the  application  to  the  muscle  must  have  a  certain  abruptness. 
For  example,  a  comparatively  weak  galvanic  current  suffices  to  stimulate  a 
muscle  to  action  when  suddenly  applied  in  full  force.  But  if  the  electric 
current  be  applied  very  gradually,  a  current  many  times  stronger  will  fail  to 
arouse  contraction  of  a  muscle. 


Necessary  Apparatus  used  to  Produce  and  Record  a  Muscle  Contraction.     Galvanic 

currents  are  usually  obtained   by  the  employment  of   a  continuous-current  cell  such  as 

that  of  Daniell,  by  which  an  electrical  current  which  varies  but  little  in  intensity  is  obtained. 

The    cell    (figure    314   A)    consists  of    a  positive  plate  of  well-amalgamated  zinc   im- 

A  B 


Fig.   314.— Diagram  of  a  Daniell's  Cell  .4,  Dry  Cell  B. 


444 


M  USCLE-NERVE     PII YSIOLOGY 


mersed  in  a  porous  cell  containing  dilute  sulphuric  acid;  and  this  cell  is  again  contained 
within  a  large  copper  vessel  (forming  the  negative  plate)  containing  a  saturated  solution 
of  copper  sulphate.  The  electrical  current  is  made  continuous  by  the  use  of  the  two 
fluids  in  the  following  manner.  The  action  of  the  dilute  sulphuric  acid  upon  the  zinc  plate 
partly  dissolves  it,  and  liberates  hydrogen,  and  this  gas  passes  through  the  porous  vessel,  and 
decomposes  the  copper  sulphate  into  copper  and  sulphuric  acid.  The  former  is  deposited 
upon  the  copper  plate,  and  the  latter  passes  through  the  porous  vessel  to  renew  the  sulphuric 


Fig.  315. — Du  Bois  Reymond's  Key. 

acid  which  is  being  used  up.  The  copper-sulphate  solution  is  renewed  by  crystals  of  the 
salt,  which  are  kept  on  a  little  shelf  attached  to  the  copper  plate  and  slightly  below  the 
level  of  the  solution  in  the  vessel.  The  current  of  electricity  supplied  by  this  cell  will 
continue  without  variation  for  a  considerable  time.  Other  cells,  such  as  the  dry  cell 
(which,  however,  is  adapted  to  open-circuit  work)  may  be  used  in  place  of  Daniell's.     The 


Fig.  316. — Mercury  Key. 


way  in  which  the  apparatus  is  arranged  is  to  attach  wires  to  the  copper  and  zinc  plates,  and 
to  bring  them  to  a  key,  connecting  the  wires  of  the  battery.  One  often  employed  is  Du 
Bois  Reymond's,  figure  315.  It  consists  of  two  pieces  of  brass  about  an  inch  long,  in  each 
of  which  are  two  holes  for  wires  and  binding-screws,  to  hold  them  tightly.  These  pieces 
of  brass  are  fixed  upon  a  vulcanite  plate  to  the  under  surface  of  which  is  attached  a  screw 


APPARATUS     USED     TO     PRODUCE     MUSCLE     CONTRACTION 


445 


clamp  by  which  it  can  be  secured  to  the  table.  The  interval  between  the  pieces  of  brass 
can  be  bridged  over  by  means  of  a  third  thinner  piece  of  similar  metal  fixed  by  a  screw  to 
one  of  the  brass  pieces,  and  capable  of  movement  by  a  handle  at  right  angles,  so  as  to  touch 
the  other  piece  of  brass.  If  the  wires  from  the  battery  are  brought  to  the  inner  binding- 
screws,  and  the  bridge  connects  them,  the  current  passes  across  it  and  back  to  the  battery. 
Wires  are  connected  with  the  outer  binding-screws,  and  the  other  ends  are  joined  together 
for  about  two  inches,  but,  being  covered  except  at  their  points,  are  insulated;  the  un- 
covered points  are  about  an  eighth  of  an  inch  apart.  These  wires  are  the  electrodes,  and  the 
electrical  stimulus  is  applied  to  the  muscle  through  them,  if  they  are  placed  behind  its 
nerve.  When  the  connection  between  the  two  brass  plates  of  the  key  is  broken  by  depress- 
ing the  handle  of  the  bridge,  the  key  is  then  said  to  be  opened. 

An  induced  current  is  developed  by  means  of  an  apparatus  called  an  induction  coil, 
and  the  one  most  employed  for  physiological  purposes  is  Du  Bois  Reymond's,  the  one 
seen  in  figure  317. 

Wires  from  a  battery  are  brought  to  the  two  binding-screws,  d'  and  d,  a  key  intervening. 
These  binding-screws  are  the  ends  of  a  coil  of  coarse  covered  wire,  c,  called  the  primary  coil. 


Fig.  317. — Du  Bois  Reymond's  Induction  Coil. 


The  ends  of  a  coil  of  finer  covered  wire,  g,  are  attached  to  two  binding-screws  to  the  left  of 
the  figure,  one  only  of  which  is  visible.  This  is  the  secondary  coil,  and  is  capable  of  being 
moved  nearer  to  c  along  a  groove  and  graduated  scale.  To  the  binding-screws  to  the  left 
of  g,  the  wires  or  electrodes  used  to  stimulate  the  muscle  are  attached.  If  the  key  in  the  cir- 
cuit of  wires  from  the  battery  to  the  primary  coil  (primary  circuit)  be  closed,  the  current 
from  the  battery  passes  through  the  primary  coil,  and  across  the  key  to  the  battery,  and 
continues  to  pass  as  long  as  the  key  continues  closed.  At  the  moment  of  closure  of  the  key, 
at  the  exact  instant  of  the  completion  of  the  primary  circuit,  an  instantaneous  current  of 
electricity  is  induced  in  the  secondary  coil,  g,  if  it  be  sufficiently  near  and  in  line  with  the 
primary  coil;  and  the  nearer  it  is  to  c,  the  stronger  is  the  current  induced.  The  current 
is  only  momentary  in  duration  and  does  not  continue  during  the  whole  of  the  period  while 
the  primary  circuit  is  complete.  When,  however,  the  primary  current  is  broken  by  open- 
ing the  key,  a  second  current,  also  momentary,  is  induced  in  g.  The  former  induced  cur- 
rent is  called  the  making  and  the  latter  the  breaking  shock;  the  former  is  in  the  opposite 
direction  to,  and  the  latter  in  the  same  direction  as,  the  primary  current. 

The  induction  coil  may  be  used  to  produce  a  rapid  series  of  shocks  by  means  of  the 
accessory  apparatus  at  the  right  of  the  figure,  called  the  magnetic  interrupter.  If  the  wires 
from  a  battery  are  connected  with  the  two  pillars  by  the  binding-screws,  one  below  c,  and 
theotherata,  the  course  of  the  current  is  indicated  by  the  arrows  in  figure  318.  The  cur- 
rent passes  up  the  pillar  from  e,  and  along  the  springs  if  the  end  of  d!  is  close  to  the  spring, 


446 


MUSCLE-NERVE     PHYSIOLOG1 


then  to  the  primary  coil  c,  and  to  wires  covering  two  upright  pillars  of  soft  iron,  b,  to  the 
pillar  a,  and  out  by  the  wires  to  the  battery.  In  passing  along  the  wire  b  the  soft  iron  is 
converted  into  a  magnet,  and  so  attracts  the  hammer,  /,  of  the  spring,  breaks  the  connection 
of  the  spring  with  d',  and  so  cuts  off  the  current  from  the  primary  coil,  and  also  from  the 
electro-magnet.  As  the  pillars,  b,  are  no  longer  magnetized  the  spring  is  released,  and  the 
current  passes  in  the  first  direction,  and  is  in  like  manner  interrupted.  At  each  make  and 
break  of  the  primary  current,  currents  corresponding  are  induced  in  the  secondary  coil. 
These  currents  are  opposite  in  direction,  but  are  not  equal  in  intensity,  the  break  shock 
being  greater.  In  order  that  the  shocks  should  be  nearly  equal  at  the  make  and  break, 
a  wire,  figure  318,  e,  connects  e  and  d',  and  the  screw  d'  is  raised  out  of  reach  of  the  spring, 
and  d  is  raised  as  in  figure  318,  so  that  part  of  the  current  always  passes  through  the 
primary  coil  and  electro-magnet.     When  the  spring  touches  d  the  current  in  b  is  diminished, 


Fig.  318. — Diagram  of  the  Course  of  the  Current  in  the  Magnetic  Interrupter  of  Du  Bois 
Reymond's  Induction  Coil.      (Helmholz's  modification.) 


but  never  entirely  withdrawn,  and  the  primary  current  is  altered  in  intensity  at  each  con- 
tact of  the  spring  with  d,  but  never  entirely  broken. 

Preparation  of  a  Muscle  for  Contraction  under  Stimuli.  The  muscles  of  the  frog 
are  most  convenient  for  the  purpose  of  recording  contractions.  The  frog  is  pithed,  that 
is  to  say,  its  central  nervous  system  is  entirely  destroyed  by  the  insertion  of  a  stout  needle 
into  the  spinal  cord,  and  the  parts  above  it.  One  of  its  lower  extremities  is  used  in  the 
following  manner.  The  large  trunk  of  the  sciatic  nerve  is  dissected  out  at  the  back  of  the 
thigh,  and  a  pair  of  electrodes  is  inserted  behind  it.  The  tendo  Achillis  is  divided  from 
its  attachment  to  the  os  calcis,  and  a  ligature  tightly  tied  round  it.  This  is  the  tendon 
of  the  gastrocnemius,  which  arises  from  above  the  condyles  of  the  femur.  The  femur  is 
now  fixed  to  a  board  covered  with  cork,  and  the  ligature  attached  to  the  tendon  is  tied  to 
the  upright  of  the  muscle  lever,  figure  319,  B.  When  the  muscle  contracts  the  lever  is 
raised.  It  is  necessary  to  attach  a  small  weight  to  the  lever.  In  this  arrangement  the 
muscle  is  in  situ,  and  the  nerve  disturbed  from  its  relations  as  little  as  possible. 

The  muscle  may,  however,  be  detached  from  the  body  with  the  lower  end  of  the  femur 
from  which  it  arises,  and  the  nerve  going  to  it  may  be  taken  away  with  it.  The  femur 
should  be  divided  at  about  the  lower  third,  and  the  bone  fixed  in  a  firm  clamp ;  the  nerve 
is  placed  upon  two  electrodes  connected  with  an  induction  apparatus,  and  the  lower  end 
of  the  muscle  is  connected  by  its  tendon  with  a  lever  which  can  write  on  a  recording 
apparatus. 

To  prevent  evaporation  this  so-called  muscle-nerve  preparation  is  placed  under  a  glass 
cover  {moist  chamber,  figure  350).  The  air  in  the  moist  chamber  is  kept  moist  by  means 
of  water  adherent  to  its  sides. 

Recording  the  Effects  of  a  Single  Induction  Shock.  With  a  muscle-nerve  preparation 
arranged  in  either  of  the  above  ways,  on  closing  or  opening  the  key  in  the  primary  circuit 
we  obtain  and  can  record  a  contraction,  and  if  we  use  the  clock-work  apparatus  revolving 
rapidly,  a  curve  is  traced  such  as  is  shown  in  figure  320. 


CONDUCTIVITY    IN    MUSCLE 


447 


Another  way  of  recording  the  contraction  is  by  use  of  the  pendulum  myograph,  figure 
352.  Here  the  swing  of  the  pendulum  along  a  certain  arc  is  substituted  for  the  clock- 
driven  movement  of  the  other  apparatus.  The  pendulum  carries  a  smoked-glass  plate  upon 
which  the  writing  lever  of  a  myograph  is  made  to  mark.     The  opening  or  breaking  shock 


Fig.  319. — Arrangement  of  the  Apparatus  Necessary  for  Recording  Muscle  Contractions 
with  a  Revolving  Cylinder  Carrying  Smoked  Paper.  A,  Revolving  cylinder;  B,  the  frog  arranged 
upon  a  cork-covered  board  which  is  capable  of  being  raised  or  lowered  on  the  upright.,  which 
also  can  be  moved  along  a  solid  triangular  bar  of  metal  attached  to  the  base  of  the  recording  ap- 
paratus— the  tendon  of  the  gastrocnemius  is  attached  to  the  writing  lever,  properly  weighted, 
by  a  ligature.  The  electrodes  from  the  secondary  coil  pass  to  the  apparatus — being,  for  the  sake 
of  convenience,  first  of  all  brought  10  a  key,  D  (Du  Bcis  Reymond's);  C.  the  induction  coil,  F, 
the  battery  (in  this  figure  a  bichromate  one);    E,  the  key  (Morse's)  in  the  primary  circuit. 

is  sent  into  the  nerve-muscle  preparation  by  the  pendulum  in  its  swing  opening  a  key, 
figure  352,  C,  in  the  primary  circuit.  A  muscle  or  its  nerve  is  more  irritable  to  an  opening 
shock  than  it  is  to  a  closing  shock  of  the  same  strength,  because  the  duration  of  the  former 
is  shorter  than  that  of  the  latter. 


Conductivity  in  Muscle.  In  an  ameba  or  other  simple  undiffer- 
entiated contractile  protoplasmic  unit  a  stimulus  applied  at  any  point  is 
quickly  transmitted  throughout  the  entire  mass.  Just  so  is  it  with  differenti- 
ated muscle.  A  stimulus  applied  at  any  point  of  a  muscle  will  quickly  be 
propagated  through  the  mass  as  far  as  there  is  protoplasmic  continuity.  In 
cardiac  muscle  and  in  smooth  muscle  there  is  uninterrupted  conduction  from 
cell  to  cell.  But  in  voluntary  muscle  each  fiber  is  physiologically  isolated  from 
its  neighbors.  When  a  voluntary  muscle  fiber  is  stimulated  either  at  the  ex- 
tremities or  at  its  middle,  the  effect  of  the  stimulus  quickly  passes  through  the 
entire  fiber,  whether  it  arouses  a  distinct  act  of  contraction  or  not. 


448  MUSCLE-NERVE    PHYSIOLOGY 

The  rate  at  which  conduction  takes  place  when  a  contraction  accompanies 
it  has  been  carefully  measured  by  numerous  observers.  It  varies  greatly 
in  the  different  kinds  of  muscle,  from  two-tenths  of  a  meter  per  second  in  the 
rabbits'  ureter  (Engelmann  )  to  ten  meters  per  second  in  the  voluntary  muscles 
of  man. 

SINGLE    MUSCLE    CONTRACTIONS. 

Characteristics  of  a  Single  Contraction.  The  Myogram.  The  con- 
traction of  a  muscle  in  response  to  a  single  effective  stimulus  of  short 
duration  is  called  a  simple  muscle  contraction.  A  record  of  such  a  contraction 
is  called  a  myogram.  The  character  of  the  myogram,  and  therefore  the  facts 
revealed  by  it,  are  dependent  on  whether  or  not  the  record  is  made  on  a  rapidly 
moving  recording  surface.  If  the  myogram  is  made  on  a  recording  surface 
that  is  standing  still,  then  it  shows  merely  the  extent  of  shortening  of  the 
muscle.  The  amount  of  shortening  for  a  given  muscle  will  depend  on  a  series 
of  conditions,  such  as  nutrition,  load,  temperature,  etc.,  all  of  which  will 
be  discussed  presently. 

When  the  record  is  made  on  a  rapidly  moving  drum  or  on  the  pendulum 
myograph,  it  is  revealed  that  the  simple  contraction  occupies  a  definite  period 
;f  time  with  well-marked  periods  or  phases.     Although  the  stimulus  may  be 


Fig.  320. — Record  of  a  Simple  Contraction  of  the  Gastrocnemius  of  the  Frog.  Time  in  .01 
seconds.  St,  Moment  of  stimulation.  Record  taken  on  a  rapid  drum  that  was  provided  with 
an  automatic  key. 

practically  instantaneous,  the  contraction  lasts  a  considerable  fraction  of  a 
second,  in  the  frog's  gastrocnemius  about  o.i  of  a  second. 

It  will  be  observed  that  after  the  stimulus  has  been  applied,  as  indicated 
by  the  vertical  line  St,  there  is  an  interval  before  contraction  commences. 
This  interval,  termed  the  latent  period,  when  measured  by  the  number  of  vi- 
brations of  the  tuning-fork  directly  beneath,  is  found  to  be  about  o.oi  of  a 
second.  The  latent  period  is  longer  in  some  muscles  than  in  others,  and 
differs  also  according  to  the  condition  of  the  muscle  and  the  kind  of  stimulus 
employed.     During  the  latent  period  there  is  no  apparent  change  in  the 


CHANGE     IN    SHAPE     DURING     MUSCULAR     CONTRACTION  449 

muscle.  The  second  part  of  the  record  shows  the  contraction  phase  proper. 
The  lever  is  raised  by  the  sudden  shortening  of  the  muscle.  The  contrac- 
tion is  at  first  very  rapid,  but  then  progresses  more  slowly  to  its  maximum. 
It  occupies  on  an  average  0.04  of  a  second  in  the  frog's  gastrocnemius.  The 
third  stage  is  the  relaxation  phase.  After  reaching  its  highest  point,  the  lever 
begins  to  descend,  in  consequence  of  the  elongation  of  the  muscle.  At  first 
the  fall  is  rapid,  but  it  then  becomes  more  gradual  until  the  lever  reaches  the 
abscissa  or  base  line,  when  the  muscle  has  attained  its  precontraction  length. 
The  stage  occupies  0.05  of  a  second.  Usually  after  the  contraction  proper 
is  over  the  lever  oscillates  below  and  above  the  base  line  in  a  series  of  dimin- 
ishing waves,  the  elastic  rebound  following  movement  of  the  simple  contrac- 
tion. These  are,  of  course,  wholly  passive  and  would  occur  equally  well  if 
we  should  lift  the  weight  to  the  height  of  the  contraction,  then  simply  let  it 
fall  while  taking  a  record. 

Change  in  Shape  during  Muscular  Contraction.  There  is  a  consider- 
able difference  of  opinion  as  to  the  mode  in  which  the  transversely  striated  mus- 
cular fibers  contract.     The  most  probable  account  is  that  the  contraction  is 


mm 

■ 


Fig.  321. — The"  Microscopic  Appearances  During  a  Muscular  Contraction  in  the  Individual 
Fibrillse,  after  Engelmann.  i.  A  passive  muscle-fiber;  c  to  d  =  doubly  refractive  discs,  with  median 
disc  a  b  in  it;  h  and  g  are  lateral  discs;  f  and  e  are  secondary  discs,  only  slightly  doubly  refractive: 
figure  on  right  same  fiber  in  polarized  light.  The  bright  part  is  doubly  refracted,  black  ends  not 
so.  2.  Transition  stage.  3.  Stage  of  entire  contraction.  In  each  case  the  right-hand  figure  repre- 
sents the  effect  of  polarized  light.      (Landois,  after  Engelmann. ,) 

effected  by  an  approximation  of  the  constituent  parts  of  the  fibrils,  which,  at  the 
instant  of  contraction,  without  any  alteration  in  their  general  direction,  become 
closer,  flatter,  and  wider,  a  condition  which  is  rendered  evident  by  the  approxi- 
mation of  the  transverse  stria?  seen  on  the  surface  of  the  fasciculus,  and  by  its  in- 
creased breadth  and  thickness.  The  appearance  of  the  zigzag  lines  into  which 
it  was  supposed  the  fibers  are  thrown  in  contraction  is  due  to  the  relaxation 
of  a  fiber  which  has  been  recently  contracted  and  is  not  at  once  stretched  again 
by  some  antagonist  fiber,  or  whose  extremities  are  kept  close  together  by  the 
contractions  of  other  fibers.  The  contraction  is  therefore  a  simple  and,  ac- 
cording to  Edward  Weber,  a  uniform,  simultaneous,  and  steady  shortening 
of  each  fiber  and  its  contents.  What  each  fibril  or  fiber  loses  in  length,  it  gains 
in  thickness.  The  contraction  is  a  change  of  form,  not  of  size;  it  is,  therefore, 
not  attended  with  any  diminution  in  bulk  from  condensation  of  the  tissue. 
29 


450 


MUSCLE-NERVE    PHYSIOLOGY 


This  has  been  proved  for  entire  muscles,  by  making  a  mass  of  muscles,  or  many 
fibers  together,  contract  in  a  vessel  full  of  water,  with  which  a  fine,  perpen- 
dicular, graduated  tube  communicates.  Any  diminution  of  the  bulk  of  the 
contracting  muscle  would  be  attended  by  a  fall  of  fluid  in  the  tube;  but  when 


Fig.  322. — Reflecting  Galvanometer.  (Thomson.)  A,  The  galvanometer,  which  consists  of 
two  systems  of  small  astatic  needles  suspended  by  a  fine  hair  from  a  support,  so  that  each  set  of 
needles  is  within  a  coil  of  fine  insulated  copper  wire;  that  forming  the  lower  coil  is  wound  in  an 
opposite  direction  to  the  upper.  Attached  to  the  upper  set  of  needles  is  a  small  mirror  about 
%  inch  in  diameter;  the  light  from  the  lamp  at  B  is  thrown  upon  this  little  mirror,  and  is  reflected 
upon  the  scale  on  the  other  side  of  B.  not  shown  in  figure.  The  coils  it  are  arranged  upon  brass 
uprights,  and  their  ends  are  carried  to  the  binding-screws.  The  whole  apparatus  is  placed  upon  a 
vulcanite  plate  capable  of  being  leveled  by  the  screw  supports,  and  is  covered  by  a  brass-bound 
glass  -.hade,  /,  the  cover  of  which  is  also  of  brass,  and  supports  a  brass  rod,  b,  on  which  moves  a  weak 
curved  magnet,  m.  C  is  the  shunt  by  means  of  which  the  amount  of  current  sent  into  the  galvanom- 
eter may  be  regulated.  When  in  use,  the  scale  is  placed  about  three  feet  from  the  galvanometer, 
which  is  a  r  .nged  east  and  west,  the  lamp  is  lighted,  the  mirror  is  rr.ade  to  swing,  and  the  light  from 
the  lamp  is  adjusted  to  fall  upon  it,  and  it  is  then  regulated  un:il  the  reflected  spot  of  light  from  it 
falls  upon  the  zero  of  the  scale.  The  wires  from  the  non-polarizable  electrodes  touching  the  muscle 
are  attached  to  the  outer  binding-screws  of  the  galvanometer,  a  key  intervening  for  short-circuiting; 
or  if  a  portion  only  of  the  current  is  to  pass  into  the  galvanometer  the  shunt  should  intervene 
as  well  with  the  appropriate  plug  in.  When  a  current  passes  into  the  galvanometer  the  needles 
and,  with  them,  the  mirror  are  turned  to  the  right  or  left  according  to  the  direction  of  the  cur- 
rent. The  amount  of  the  deflection  of  the  needle  is  marked  on  the  scale  by  the  spot  of  light  traveling 
along  it. 

the  experiment  is  carefully  performed,  the  level  of  the  water  in  the  tube  re- 
mains the  same,  whether  the  muscle  be  contracted  or  not. 

In  thus  shortening,  muscles  appear  to  swell  up,  becoming  rounder,  more 
prominent,  harder,  and  apparently  tougher.  But  this  hardness  of  muscle  in 
the  state  of  contraction  is  not  due  to  increased  firmness  or  condensation  of  the 


CHEMICAL     CHANGES     IN     CONTRACTING     MUSCLE  451 

muscular  tissue,  but  to  the  increased  tension  to  which  the  fibers,  as  well  as  their 
tendons  and  other  tissues,  are  subjected  from  the  resistance  ordinarily  opposed 
to  their  contraction.  When  no  resistance  is  offered,  as  when  a  muscle  is  cut 
off  from  its  tendon,  not  only  is  no  hardness  perceived  during  contraction,  but 
the  muscular  tissue  is  even  softer  and  more  extensible  than  in  its  ordinary 
uncontracted  state.  During  contraction  in  each  fiber  it  is  said  that  the  aniso- 
tropous  or  doubly  refractive  elements  become  less  refractive  and  the  singly 
refractive  more  so,  figure  321. 

Chemical  Changes  in  Contracting  Muscle.  1.  The  reaction  of  the 
muscle,  which  is  normally  alkaline  or  neutral,  becomes  decidedly  acid  during 
contraction,  from  the  development  of  sarcolactic  acid.  2.  The  muscle  gives 
out  carbon  dioxide  gas  and  takes  up  oxygen.  The  amount  of  the  carbon  dioxide 
given  out  does  not  appear  to  be  entirely  dependent  upon  the  oxygen  taken  in, 
and  so  doubtless  in  part  arises  from  some  other  source.     Muscle  contracts  in 


Fig.  323. — Diagram  of  Du  Bois  Reymond's  Non-polarizable  Electrodes,  a,  Glass  tube  filled 
with  a  saturated  solution  of  zinc  sulphate,  in  the  end,  r,  of  which  is  china  clay  drawn  out  to  a 
point;  in  the  solution  a  well-amalgamated  zinc  rod  is  immersed  and  connected,  by  means  of  the 
wire  which  passes  through  a,  with  the  galvanometer.  The  remainder  of  the  apparatus  is  simply 
for  convenience  of  application.  The  muscle  and  the  end  of  the  second  electrode  are  to  the  right 
of  the  figure. 

an  atmosphere  of  hydrogen,  showing  that  oxygen  is  present  in  fixed  combina- 
tion. A  muscle,  however,  contracts  for  a  longer  time  in  an  atmosphere  of 
oxygen.  3.  Certain  imperfectly  understood  chemical  changes  occur,  in  all 
probability  connected  with  1  and  2,  in  which  glycogen  is  diminished,  and 
glucose  and  muscle  sugar,  inosite,  appear.  The  nitrogenous  extractives  are 
also  increased. 

Electrical  Changes  in  Contracting  Muscle.  Resting  muscles  un- 
injured in  the  body  have  a  uniform  potential,  are  isoelectric.  But  when 
removed  from  the  body  they  are  more  or  less  injured  and,  therefore,  show 
differences  of  electrical  potential  between  different  points  on  the  muscle, 
called  currents  of  injury  or  demarcation  currents. 


452 


MUSCLE-NERVE     PHYSIOLOGY 


The  Demonstration  of  Muscle  Currents.  The  demonstration  of  electrical  currents 
in  muscle  requires  a  galvanometer  and  non-polarizing  electrodes.  A  muscle  prism  is 
insulated,  and  a  pair  of  non-polarizable  electrodes  connected  with  a  very  delicate  galva- 
nometer, figure  322,  are  applied  to  various  points  of  the  prism;  and  by  a  deflection  of  the 
needle-  to  a  greater  or  less  extent  in  one  direction  or  another,  the  strength  and  direction  of 
the  currents  in  the  piece  of  muscle  can  be  determined.  It  is  necessary  to  use  non-polariz- 
able and  not  metallic  electrodes  in  this  experiment,  as  otherwise  there  is  no  certainty  that 
the  whole  of  the  current  observed  is  communicated  from  the  muscle  itself  and  not  derived 
from  the  metallic  electrodes  and  arising  in  consequence  of  the  action  of  the  saline  juices  of 
the  tissues  upon  them.  The  form  of  the  non-polarizable  electrodes  is  a  modification  of  Du 
Bois  Reymond's  apparatus,  figure  323,  which  consists  of  a  somewhat  flattened  glass  cyl- 
inder, a,  drawn  abruptly  to  a  point,  and  fitted  to  a  socket  capable  of  movement,  and  at- 
tached to  a  stand,  A,  so  that  it  can  be  raised  or  lowered  as  required.  The  lower  portion  of 
the  cylinder  is  filled  with  china  clay  moistened  with  saline  solution,  part  of  which  projects 
through  its  drawn-out  point;  the  rest  of  the  cylinder  is  filled  with  a  saturated  solution  of 
zinc  sulphate  into  which  dips  a  well -amalgamated  piece  of  zinc  connected  by  means  of  a  wire 
with  the  galvanometer.  In  this  way  the  zinc  sulphate  forms  a  homogeneous  and  non- 
polarizable  conductor  between  the  zinc  and  the  china  clay.  A  second  electrode  of  the 
same  kind  is,  of  course,  necessary.  Recently  Porter  has  devised  a  boot-shaped  clay 
electrode  that  is  burned  and  hence  has  the  immense  advantage  of  permanency. 

Currents  of  Injury,  or  Demarcation  Currents.  If  a  segment  is  cut 
out  of  a  living  gastrocnemius,  its  cut  ends  present  regions  of  maximal  injury. 
Such  a  preparation  is  called  a  muscle  prism. 

If  the  points  on  the  surface  of  a  muscle  prism  be  connected  with  the  gal- 
vanometer by  non-polarizable  electrodes,  it  will  be  found  that  the  currents 
pass  from  point  to  point,  as  shown  in  the  diagram,  figure  324. 


Fig.  324. — Diagram  of  the  Currents  in  a  Muscle  Prism.      (Du  Bois  Reymond.) 


The  strongest  currents  pass  from  the  equator  to  a  point  representing  the 
middle  of  the  cut  ends;  currents  also  pass  from  points  nearer  the  equator  to 
those  more  remote,  but  not  from  points  equally  distant,  which  are  isoelectric 
points.  The  cut  ends  are  always  negative  to  the  equator.  The  currents  are 
in  all  probability  due  to  chemical  changes  going  on  in  the  muscles  at  the  in- 
jured ends. 

Action  Currents.  When  a  muscle  is  made  to  contract  the  demar- 
cation current  undergoes  a  sharp  decrease  as  shown  by  the  deflection  of  the 
galvanometer  needle,  which  swings  back  in  the  direction  of  equilibrium. 


HEAT     PRODUCED     IN    A     SIMPLE     CONTRACTION  453 

This  deflection,  originally  called  the  current  of  negative  variation,  has  been 
shown  to  be  due  to  the  processes  going  on  in  the  muscle  during  contraction 
and  is  therefore  called  the  action  current.  It  occurs  where  no  previous  demar- 
cation current  exists. 

For  the  study  of  the  action  current  the  capillary  electrometer  is  very  con- 
venient. The  hearts  of  cold-blooded  animals,  because  of  their  slow  con- 
traction, serve  well  for  demonstration.  The  muscle  contraction  passes  over 
the  ventricle  in  the  form  of  a  wave,  the  electric  potential  of  the  muscle  changing 
as  it  becomes  active  or  passive.  For  any  two  points  on  the  heart  muscle, 
therefore,  there  will  be  two  changes  of  potential,  the  active  part  first  becom- 
ing negative  to  the  inactive,  and  then,  as  the  wave  passes  down  and  the  in- 


Fig.  325.— Figure  for  Work  Energy,  Showing  Height  of  the  Contraction  of  the  Gastrocnemius 
of  the  Frog  with  Loads  Increased  by  Ten  Grams  at  a  Time. 

active  part  becomes  active,  the  current  is  reversed.  This  is  known  as  a 
diphasic  current. 

In  certain  fishes  definite  electrical  organs  exist,  organs  which  are  derived 
from  muscle-like  tissues  and  which  may  be  regarded  morphologically  as  mus- 
cles highly  specialized  for  the  production  of  energy  in  the  form  of  electricity. 

Heat  Produced  in  a  Simple  Contraction.  Becquerel  and  Breschet 
found,  with  the  thermo-multiplier,  about  0.50  C.  of  heat  produced  by  each 
forcible  contraction  of  a  man's  biceps;  and  when  the  actions  were  long  con- 
tinued, the  temperature  of  the  muscle  increased  i°  C.  In  the  frog's  muscle 
a  considerable  number  of  contractions  have  been  found  to  produce  an  ele- 
vation of  temperature  equal  on  an  average  to  less  than  0.20  C,  while  a  single 
contraction  produces,  according  to  R.  Heidenhain,  from  0.0010  to  0.0050  C. 
One  gram  of  frog's  muscle  will  produce  in  a  single  maximal  contraction  about 
0.003  calorie  or  the  equivalent  of  126  gramcentimeters  of  work  energy  (since 
1  calorie  =  0.425  kilogrammeter  of  work).  The  cause  of  the  rise  of  tempera- 
ture is  the  increased  chemical  activity  at  the  time  of  contraction.  As  we 
have  already  seen,  in  the  chapter  on  Animal  Heat,  muscles  have  the  power  of 
producing  heat  even  when  not  contracted. 


454       .  MUSCLE-NERVE     PHYSIOLOGY 

The  amount  of  heat  energy  developed  during  a  single  contraction  will  vary- 
sharply  according  to  the  tension  under  which  the  muscle  contracts.  The  heat 
production  follows  closely  the  energy  of  work  produced,  and  apparently 
obeys  the  same  laws. 

The  Work  Energy  Liberated  by  a  Simple  Muscle  Contraction.  When 
a  muscle  contracts  against  a  resistance  and  a  load  is  moved,  work 
energy  is  liberated.  In  fact  the  liberation  of  work  energy  and  heat  energy 
are  the  specific  functions  of  the  muscles  among  the  warm-blooded  animals. 
A  frog's  gastrocnemius  weighing  i  gram  and  loaded  with  50  grams  will 
contract  from  0.5  to  0.6  cm,  i.e.,  will  do  25  to  30  gramcentimeters  of  work 
for  each  simple  contraction.     The  amount  of  work  done  is  intimately  associ- 

Table  Showing  the  Relation  Between  Load  and  Work. 


i  or  Tension. 
Grams. 

Height  Lifted. 
Centimeters. 

Work  Done. 
Gramcentimeters. 

O 

1.2 

O 

40 

So 

120 

160 

O.S 

O.4 
0.2 

32 
40 
4S 
32 

200 

O.I 

20 

240 

O.O 

0 

ated  with  the  tension  under  which  the  muscle  contracts.  As  the  tension  in- 
creases from  no  load  up  to  100  or  150  grams  (for  a  i-gram  muscle),  the  work 
increases.  But  as  the  tension  continues  to  increase,  the  work  falls  off  until 
a  point  is  reached  at  which  the  load  is  not  lifted  at  all. 

CONDITIONS   WHICH   AFFECT   THE    IRRITABILITY    OF 

THE   MUSCLE   AND    THE    CHARACTER   OF   THE 

CONTRACTION. 

There  are  a  number  of  conditions  which  influence  both  the  irritability 
of  a  muscle  and  the  power  and  character  of  its  contractions.  Irritability 
and  contractility  may  vary  independently,  but  as  a  rule  any  condition  which 
decreases  the  one  also  decreases  the  other.  The  most  important  of  these 
conditions  are:  relation  of  the  muscle  to  the  central  nervous  system,  con- 
dition of  nutrition,  stimulus,  temperature,  fatigue,  drugs,  disease,  etc. 

Effect  of  the  Strength  of  Stimulus.  A  strength  of  current  that  is 
just  sufficient  to  give  the  contraction  of  a  muscle  is  called  a  minimal  stimulus. 
This  is  a  comparatively  weak  induction  current,  one  which  can  scarcely  be 
detected  by  the  tip  of  the  tongue.  As  the  strength  of  the  current  is  very 
gradually  increased,  the  height  of  the  contraction  curve  increases  until  the 
maximal  stimulus  is  reached,  which  produces  a  contraction  of  an  amplitude 
beyond  which  no  increase  occurs  even  though  the  strength  of  the  stimulus  be 


THE     INFLUENCE     OF     REPEATED     ACTIVITY  455 

multiplied  many  fold.  The  range  between  the  strengths  of  the  minimal  and 
maximal  stimuli  is  very  restricted  indeed.  The  absolute  strength  of  a  mini- 
mal stimulus  varies  exceedingly  for  a  given  muscle,  depending  on  its  degree 
of  irritability.  This  narrow  range  between  minimal  and  maximal  stimuli 
serves  as  a  convenient  means  for  detecting  the  variations  in  irritability.  One 
should  count  on  a  continued  decrease  in  irritability  in  isolated  muscles,  hence 


Fig.  326. — Contraction  of  the  Gastrocnemius  Under  the  Influence  of  Variation  of  Strength  of 
Stimulus.  The  muscle  was  stimulated  by  Pet7old's  inductorium,  graduated  to  show  units  of 
current.     The  figures  6,  7,  8,  9,  10,  etc..  indicate  relative  strength  of  stimulus. 

should  choose  a  supramaximal  stimulus  for  all  such  preparations  when  other 
conditions  surrounding  the  muscle  are  under  investigation. 

The  Influence  of  Repeated  Activity.  The  irritability  of  muscle  is 
decreased  by  undue  functional" activity.  The  cause  of  the  diminished  ir- 
ritability is  twofold:  when  a  muscle  contracts,  part  of  its  substance  is  ex- 
pended, part  of  its  store  of  nutriment  is  exhausted,  and  it  cannot  contract  so 
vigorously  again  until  the  loss  is  made  up.  To  this  extent  fatigue  has  much 
the  same  effect  as  cutting  off  or  diminishing  the  blood  supply.  The  other 
cause  for  the  diminution  of  irritability  is  the  accumulation  of  poisonous  prod- 
ucts in  the  muscle,  substances  generated  during  contraction,  probably  sar- 
colactic  acid  chiefly.  In  a  living  animal  these  poisonous  products  exert  their 
influence  not  only  upon  the  muscle  or  muscles  immediately  concerned  in 
contraction,  but  upon  the  musculature  of  the  body  generally,  and  the  effect 
remains  until  they  are  eliminated  from  the  body.  Massage  of  the  muscles 
increases  the  passage  of  waste  products  into  the  general  blood  stream  and  the 
rapidity  of  their  elimination. 

In  the  first  few  simple  contractions,  repeated  in  series,  there  is  an  increase 
in  the  amplitude  of  the  contractions  resulting  in  the  phenomenon  known 
as  staircase  contractions  or  "Treppe."     This  stage  is  followed  by  a  period 


456 


MUSCLK-N  ERV  E     PH  YSIOLOG  Y 


of  sustained  contractions,  and  this  finally  by  a  diminishing  series  of  amplitudes 
until  the  muscle  fails  to  respond.  After  a  few  minutes'  rest  a  muscle  will 
again  give  strong  contractions,  but  only  for  a  brief  series. 

If  the  time  of  the  simple  contractions  is  measured,  it  will  be  found,  figure 
327,  that  not  only  is  the  amplitude  decreased  but  the  duration  is  greatly 
increased  as  the  contractions  are  repeated.  The  latent  period  changes  very 
little.  The  contraction  phase  is  considerably  prolonged,  but  the  relaxation 
phase  is  very  greatly  increased.  As  fatigue  progresses,  the  total  time  of  the 
simple  contraction  may  be  two  or  three  times  longer  than  the  normal.     The 


Fig.  327. — Contractions  of  the  Gastrocnemius  Muscle  to  Show  Fatigue.     The  numbers  printed 
on  the  figure  indicate  the  contractions  in  the  series  which  is  recorded.      (.Lee.; 

ability  of  the  muscle  to  do  work  falls  off  rapidly,  of  course;  and  the  greater 
the  load  during  the  time  fatigue  is  coming  on,  the  more  quickly  complete 
fatigue  approaches. 

The  Influence  of  Temperature.  The  irritability  of  muscle  is  in- 
creased by  raising  its  temperature  slightly  above  that  of  the  animal  from 
which  it  has  been  taken,  while  it  is  decreased  by  cooling.     If,  however,  the 


Fig.  328. — Contractions  of  the  Gastrocnemius  Muscle  to  Show  the  Influence  of  Temperature 
on  the  Amplitude'of  the  Contractions.  At  400  C.  the  muscle  has  begun  to  pass  into  rigor  mortis, 
yet  is  able  to  give  short  contractions.  The  steps  on  the  curve  of  rigor  at  the  right  occur  at  tem- 
peratures of  410,  420,  and  430  C. 


THE  INFLUENCE  OF  TEMPERATURE 


457 


temperature  be  raised  too  high  (400  C.  for  frog,  500  C.  for  mammal),  the 
muscle  enters  into  a  condition  of  heat  rigor  and  its  irritability  is  forever  lost. 
After  cooling,  unless  the  cold  be  too  severe  and  prolonged,  the  irritability  re- 
turns as  the  temperature  is  raised.  A  series  of  vertical  records  of  simple  contrac- 
tions beginning  at  room  temperature  and  decreasing  with  a  contraction  at  each 
fall  of  one  degree  reveals  the  fact  that  the  amplitude  falls  off  slowly  until  a 
temperature  of  120  to  io°  C.  is  reached,  then  as  gradually  increases  until  40  to 
20  C,  after  which  the  amplitude  drops  off  sharply  to  about  — 1°  C.  However, 
this  phenomenon  is  partly  one  of  irritability,  since  a  very  strong  stimulus  will 
produce  a  vigorous  contraction  until  the  muscle  begins  to  freeze.  If  at  the 
freezing  temperature  the  muscle  be  slowly  and  carefully  increased  in  tem- 
perature it  will  recover  from  the  effects  of  the  cooling  without  apparent  injury, 
and  will  give  a  reverse  series  to  the  one  obtained  by  decreasing  the  temperature. 


Fig.  329.— Influence  of  Temperature  on  the  Duration  of  the  Contraction  of  the  Frog's 

Gastrocnemius. 


As  the  increase  of  temperature  is  continued  above  room  temperature  the 
amplitude  of  the  contractions  very  greatly  increases  (also  the  elasticity), 
reaching  a  maximum  in  the  frog's  gastrocnemius  at  about  350  to  360  C.  The 
amplitude  sharply  decreases  above  350  C.  up  to  370  to  380  C,  where  heat 
rigor  begins  and  the  muscle  permanently  shortens.     Heat  rigor  is  usually 


458  MUSCLE-NERVE     PHYSIOLOGY 

complete  at  400  to  410  C.  A  muscle  cannot  recover  its  irritability  after  heat 
rigor  has  set  in  strongly. 

If  the  time  of  the  contraction  is  measured  at  different  temperatures  it  will 
be  found  to  be  greatly  delayed  at  20  to  40  C,  and  very  much  quicker  than  nor- 
mal at  330  to  350  C.  As  in  fatigue,  the  effect  falls  chiefly  on  the  contraction  and 
relaxation  phases  and  only  slightly  on  the  latent  period.  The  latent  period 
is  more  sharply  influenced  by  temperature  than  by  fatigue. 

Influence  of  Blood  Supply.  In  the  normal  human  muscle  there 
is  a  delicately  balanced  vaso-motor  mechanism  by  which  the  amount  of  blood 
flowing:  through  a  muscle  is  immediately  increased  when  the  muscle  is  in  con- 
traction.  This  blood  stream  is  of  course  carrying  nutritive  materials  to  the 
muscle  and  taking  away  wastes.  If  the  blood  supply  to  a  muscle  is  cut  off, 
then  the  muscle  can  only  draw  on  its  stored  supply  of  potential  energy,  which  in 
active  contraction  is  sooner  or  later  exhausted.  Under  such  conditions  the 
muscle  increases  in  irritability  for  a  few  minutes  and  then  gradually  loses 
both  its  irritability  and  its  power  to  contract.  Even  mammalian  muscles 
have  been  kept  alive  and  normal  in  their  activity  for  several  hours  by  irrigat- 
ing them  with  defibrinated  and  aerated  blood  (von  Frey).  Mammalian 
muscles  will  remain  irritable  for  30  minutes,  or  longer  if  cooled,  after  being 
shut  off  from  their  blood  supply  and  isolated  from  the  body,  but  both  irrita- 
bility and  contractility  soon  disappear  entirely. 

Effect  of  Nerve  Supply.  The  voluntary  or  skeletal  muscle  normally 
contracts  in  the  body  only  when  stimulated  through  its  motor  nerve.  If  the 
motor  nerve  is  severed,  the  muscle  is  cut  off  from  its  normal  source  of  activity, 
hence  will  undergo  the  changes  resulting  from  disuse,  which  will  be  presently 
discussed.  Aside  from  this,  it  is  held  by  most  observers  that  there  are  dis- 
tinct nutritive  or  trophic  nerves  which  exercise  a  controlling  influence  over  the 
growth,  development,  and  general  nutritive  processes  going  on  in  muscle. 

When  a  motor  nerve  is  cut,  the  muscle  at  first  exhibits  heightened  irrita- 
bility to  all  forms  of  stimuli.  In  a  couple  of  weeks  it  decreases  in  its  power 
to  respond  to  rapidly  changing  stimuli  like  induced  currents.  It  responds 
more  readily  to  mechanical  shocks  and  to  galvanic  currents  for  six  or  seven 
weeks,  then  gradually  loses  the  power  of  contracting  through  as  many  months. 
The  changes  are  due  to  protoplasmic  degeneration.  It  is  not  clear  in  what 
degree  these  changes  are  due  to  loss  of  trophic  nerve  influence,  to  inac- 
tivity, and  to  changes  in  nutritive  conditions.  Since  degeneration  occurs 
when  the  vascular  supply  is  maintained,  it  would  seem  that  the  nutritive  con- 
dition must  be  chargeable  to  one  or  the  other  of  the  first  two  factors,  probably 
to  both. 

Use  of  muscle  increases  its  power  and  also  its  irritability.  A  properly 
regulated  exercise  is  well  known  to  contribute  to  the  health  and  development 
of  muscles.  In  cases  of  paralysis,  mechanical  or  electrical  stimulation  is 
applied  directly  to  the  muscle  in  an  effort  to  supply  artificial  exercise  until  the 


THE     EFFECT     OF     DRUGS  459 

nerves  are  regenerated  and  motor  connections  reestablished.  If  such  stim- 
ulation is  not  applied,  the  muscle  degenerates  from  disuse  and  loses  its  irri- 
tability often  before  the  nerves  regenerate. 

The  Effect  of  Drugs.  Drugs  affect  the  irritability  of  muscle,  some 
augmenting,  others  depressing  it.  Voluntary  muscle,  which  does  not  ordina- 
rily contract  except  when  stimulated,  can  be  made  so  irritable  by  certain 
salts  that  it  contracts  automatically  like  heart  muscle,  and  the  converse. 
Ether,  chloroform,  etc.,  anesthetize  muscle  just  as  they  do  nerve,  suppressing 
both  irritability  and  contractility.  Suprarenal  extract  increases  the  ampli- 
tude of  contraction,  as  do  also  caffeine,  digitalis,  nicotine,  and  others.  Ver- 
atrine  is  well  known  greatly  to  prolong  the  relaxation  phase  of  the  simple 
contraction  without  materially  affecting  the  contraction  phase,  or  the  latent 
period. 

TETANIC  AND  VOLUNTARY  MUSCULAR  CONTRACTIONS. 

Effect  of  Rate  of  Stimulation.  If  we  stimulate  the  muscle-nerve 
preparation  with  two  induction  shocks,  one  immediately  after  the  other,  when 
the  point  of  stimulation  of  the  second  one  corresponds  to  the  crest  of  the  con- 
traction of  the  first,  a  second  curve,  figure  330,  will  occur,  which  will  commence 
near  the  highest  point  of  the  first  and  will  rise  nearly  as  much  higher,  so  that 
the  sum  of  the  height  of  the  two  curves  almost  exactly  equals  twice  the 
height   of   the  first.     This    phenomenon   is  called  summation.     If  a  third 


Fig.  330.— Tracing  of  a  Double  Muscle-Curve.  To  be  read  from  left  to  right.  While  the 
muscle  was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  intervened  is 
indicated  by  the  dotted  line),  a  second  induction  shock  was  thrown  in.  at  such  a  time  that  the 
second  contraction  began  just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen  to 
start  from  the  first,  as  does  the  first  from  the  base  line.     (M.  Foster.) 

and  fourth  shock  be  passed,  a  similar  effect  will  ensue,  and  curves  one 
above  the  other  will  be  traced,  the  third  being  slightly  lower  than  the 
second,  and  the  fourth  than  the  third.  If  a  continuous  series  of  shocks 
occur,  however,  the  lever  after  a  time  ceases  to  rise  any  further,  and  the  con- 
traction, which  has  reached  its  maximum,  is  maintained.  The  condition 
which  ensues  is  called  Tetanus.     A  tetanus  is  really  a  summation  of  contrac- 


4«0 


MUSCLE-NERVE     PHYSIOLOGY 


tions,  but  unless  the  stimuli  become  very  rapid  indeed,  the  muscle  will  still  be 
in  a  condition  of  vibratory  contraction  and  not  of  unvarying  contraction. 

If  the  shocks,  however,  be  repeated  at  very  short  intervals,  varying,  in  the 
frog,  from  eighteen  to  thirty  per  second,  the  muscle  contracts  to  its  utmost 
at  once  and  continues  at  its  maximum  contraction  for  some  time.  The 
lever  rises  almost  perpendicularly  and  then  describes  a  straight  line,  figure 
331,  c.  The  rate  of  stimulation  required  increases  with  the  rapidity  of  the 
simple  contraction.  If  the  stimuli  are  not  so  rapid,  the  line  of  maximum  con- 
traction becomes  wavy,  indicating  a  tendency  of  the  muscle  to  relax  during 


Fig.  331. — a,  Frog's  gastrocnemius  muscle  stimulated  with  four  induction  shocks  per  second, 
showing  complete  relaxation  between  stimuli ;  b,  same  muscle  stimulated  eight  times  per 
second,  showing  partial  relaxation  between  stimuli  (incomplete  tetanus);  c,  same  muscle 
stimulated  twelve  times  per  second,  showing  development  of  an  almost  complete  tetanus. 

the  intervals  between  the  stimuli,  figure  331,  b.  As  the  muscle  becomes 
fatigued,  a  less  rapid  rate  of  stimulation  is  required  to  produce  a  complete 
tetanus,  owing  to  the  prolongation  of  the  relaxation  period  in  such  a  muscle. 
The  height  of  the  contraction,  however,  is  lessened.  This  condition  of  pro- 
longed relaxation  is  known  as  contracture. 

Coordinated  Muscular  Contractions.  In  the  human  body  the  skel- 
etal muscles  contract  only  on  stimulation  through  their  motor  nerves,  i.e., 
under  the  influence  of  nerve  impulses  that  have  their  origin  in  the  central 


MUSCLE     IN    RIGOR    MORTIS  461 

nervous  system.  Such  motor  impulses  may  arise  through  reflexes,  through 
automatic  activity  of  the  nerve  center,  or  by  higher  cerebral  origin  associated 
with  conscious  psychic  effort.  In  either  case  the  apparatus  consists  of  one 
or  more  central  neurones,  an  anterior-horn  motor  cell,  and  the  muscle 
itself.     Conscious  or  voluntary  effort  may  be  taken  as  a  type. 

Simple  contractions  are  possible  to  human  muscles,  but  undoubtedly 
tetanic  contractions  are  the  rule.  If  one  holds  the  arm  out  at  right  angles  to  the 
trunk,  the  movement  requires  the  continuous  or  tetantic  contraction  of  the 
deltoid  and  the  series  of  extensor  muscles.  If  the  arm  is  retained  in  the 
extended  position  long  enough,  extreme  fatigue  is  felt  and  presently  one  can 
no  longer  maintain  the  position.  Yet,  if  the  muscles  involved  are  immediately 
stimulated  directly  with  an  electric  current,  they  contract,  showing  that  such 
exhaustion  as  exists  is  not  wholly  due  to  the  muscle. 

Mosso's  ergograph  was  devised  for  the  specific  purpose  of  studying  the 
character  of  fatigue  of  voluntary  effort.  This  apparatus  is  adapted  to  the 
study  of  the  fatigue  of  the  flexors  of  the  middle  finger,  or,  in  the  newer  in- 
strument devised  by  Storey,  to  the  abductor  of  the  index  finger.  Numerous 
studies  have  shown,  apparently,  that  the  fatigue  of  voluntary  effort  involves, 
first,  the  nervous  apparatus  and,  later,  the  muscle;  that  the  muscle  still  retains 
a  considerable  reserve  of  energy  when  the  apparatus  as  a  whole  is*  exhausted. 

Muscle  in  Rigor  Mortis.  After  the  muscles  of  the  dead  body  have 
lost  their  irritability  or  capability  of  being  excited  to  contraction  by  the  ap- 
plication of  a  stimulus,  they  spontaneously  pass  into  a  state  of  contraction 
apparently  identical  in  effect  with  that  which  ensues  during  life.  It  affects  all 
the  muscles  of  the  body,  and,  when  external  circumstances  do  not  prevent  it, 
commonly  fixes  the  limbs  in  that  which  is  their  natural  posture  of  equilibrium 
or  rest.  From  the  simultaneous  contraction  of  all  the  muscles  of  the  trunk, 
a  general  stiffening  of  the  body  is  produced,  which  constitutes  the  rigor 
niorlis  or  post-mortem  rigidity. 

\\  hen  this  condition  has  set  in,  the  muscle  becomes  acid  in  reaction  (due  to 
development  of  sarcolactic  acid),  gives  of}  carbonic  acid  in  great  excess, 
diminishes  in  volume  slightly,  becomes  shortened  and  opaque,  its  substance  sets 
in  a  firm  coagulatio.  Rigor  comes  on  much  more  rapidly  after  muscular 
activity,  and  is  hastened  by  warmth. 

The  immediate  cause  of  rigor  seems  to  be  a  chemical  one,  namely,  the 
coagulation  of  the  muscle  plasma.  We  may  distinguish  three  main  stages; 
i.  Gradual  coagulation.  2.  Contraction  of  coagulated  muscle  clot  (myosin), 
and  3,  squeezing  out  of  muscle  serum.  During  the  first  stage,  restoration  is 
possible,  by  the  circulation  of  arterial  blood  through  the  muscles; 
and  even  when  the  second  stage  has  set  in,  vitality  may  be  restored 
by  dissolving  the  coagulum  of  the  muscle  in  salt  solution,  and  passing  arterial 
blood  through  the  vessels.  After  the  second  stage  is  advanced,  recovery  is 
impossible. 


402  MUSCLE-NERVE     PHYSIOLOGY 

It  has  been  noticed  that  the  relaxation  in  muscles  after  rigor  sometimes 
occurs  too  quickly  to  be  caused  by  putrefaction.  The  suggestion  that  in 
such  cases  the  relaxation  is  due  to  a  ferment-action  is  very  plausible. 
It  is  known  that  pepsin  is  present  in  muscles,  and  that  this  ferment  will 
act  in  an  acid  medium.  The  conditions  for  the  solution  of  the  coagulated 
myosin  are  therefore  present  since  the  reaction  of  muscle  in  rigor  is  acid. 
Subjecting  fresh  muscle  to  the  action  of  heat  (500  to  6o°  C.)  or  immersing 
it  in  distilled  water  causes  a  similar  coagulation  to  that  of  rigor  mortis. 
The  former  is  known  as  heat  rigor,  and  the  latter  as  witer  rigor. 


Fig.   332. — Curve  of  Shortening  of  [he  Gastrocnemius  Muscle  of  the  Frog,  During  Heat  Rigor. 
The  numbers  indicate  degrees  centigrade. 

The  muscles  are  not  affected  simultaneously  by  rigor  mortis.  It  affects 
the  neck  and  lower  jaw  first;  next,  the  upper  extremities,  extending  from 
above  downward;  and,  lastly,  reaches  the  lower  limbs.  In  some  rare  instances 
only,  it  affects  the  lower  extremities  before  or  simultaneously  with  the  upper 
extremities.  It  usually  ceases  in  the  order  in  which  it  begins:  first  at  the 
head,  then  in  the  upper  extremities,  and  lastly  in  the  lower  extremities.  It 
never  ordinarily  commences  earlier  than  ten  minutes,  and  never  later  than 
seven  hours  after  death;  and  its  duration  is  greater  in  proportion  to  the 
lateness  of  its  accession.  Heat  is  developed  during  the  passage  of  a  muscular 
fiber  into  the  condition  of  rigor  mortis. 

Since  rigidity  does  not  ensue  until  muscles  have  lost  the  capacity  of  being 
excited  by  external  stimuli,  it  follows  that  all  circumstances  which  cause 
a  speedy  exhaustion  of  muscular  irritability  induce  an  early  occurrence  of  the 
rigidity,  while  conditions  by  which  the  disappearance  of  the  irritability  is 
delayed  are  succeeded  by  a  tardy  onset  of  the  rigidity  of  rigor.  This  is  the 
explanation  of  its  speedy  occurrence,  and  equally  speedy  departure,  in  the 
bodies  of  persons  exhausted  by  chronic  diseases;  and  its  tardy  onset  and  long 


MUSCULAR     METABOLISM     DURING     CONTRACTION 


463 


continuance  after  sudden  death  from  acute  diseases.  In  some  cases  of  sudden 
death  from  lightning,  violent  injuries,  or  paroxysms  of  passion,  rigor  mortis  has 
been  said  not  to  occur  at  all;  but  this  is  not  always  the  case.  It  may,  indeed, 
be  doubted  whether  there  is  really  a  complete  absence  of  the  post-mortem 
rigidity  in  any  such  cases;  for  the  experiments  of  Brown-Sequard  make  it 
probable  that  the  rigidity  may  supervene  immediately  after  death,  and  then 
pass  away  with  such  rapidity  as  to  be  scarcely  observable. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous  existence 
of  paralysis  in  a  part,  provided  the  paralysis  has  not  been  attended  with  very 
imperfect  nutrition  of  the  muscular  tissue. 

The  rigidity  affects  the  involuntary  as  well  as  the  voluntary  muscles, 
whether  they  be  constructed  of  striped  or  unstriped  fibers.  The  rigidity 
of  involuntary  muscles  with  striped  fibers  is  shown  in  the  contraction  of 
the  heart  after  death.  The  contraction  of  the  muscles  with  unstriped  fibers 
is  shown  by  an  experiment  of  Valentin,  who  found  that  if  a  graduated  tube 
be  connected  with  a  portion  of  intestine  taken  from  a  recently  killed  animal, 
and  the  intestine  be  tied  at  the  opposite  end,  and  filled  with  water,  the  water 
will  in  a  few  hours  rise  to  a  considerable  height  in  the  tube,  owing  to  the  con- 
traction of  the  intestinal  walls.  It  is  still  better  shown  in  the  arteries,  of 
which  all  that  have  muscular  coats  contract  after  death,  and  thus  present  the 
roundness  and  cord-like  feel-  of  the  arteries  of  a  limb  lately  removed,  or  those 
of  a  body  recently  dead.  Subsequently  they  relax,  as  do  all  the  other  mus- 
cles, and  feel  lax  and  flabby  and  lie  as  if  flattened,  and  with  their  walls  nearly 
in  contact. 

Muscular  Metabolism  During  Contraction.  The  question  of  the 
metabolism  of  muscle  both  in  a  resting  and  in  an  active  condition  has  for 
many  years  occupied  the  attention  of  physiologists.  It  cannot  be  said  even 
now  to  be  thoroughly  understood.  Most  of  the  facts  with  reference  to  the 
subject  have  been  already  mentioned.  We  may  shortly  recapitulate  them 
here:  First,  muscle  during  rest  absorbs  oxygen  and  gives  out  carbon  dioxide. 
This  has  been  shown  by  an  analysis  of  the  gases  of  the  blood  going  to  and 
leaving  muscles.  During  activity,  e.g.,  during  tetanus,  the  same  interchange 
of  gases  takes  place,  but  the  quantities  of  the  oxygen  absorbed  and  of  the 
carbon  dioxide  given  up  are  increased,  and  the  proportion  between  them  is 
altered  thus: 


Venous  Blood. 

02,  less  than  in  Arterial 
Blood. 

C02,  more  than  in  Arterial 
Blood. 

9  per  cent 

6.71  per  cent 

12.26  per  cent 

10.79  Per  cent 

464  MUSCLE-NERVE    PHYSIOLOGY 

There  is  then  a  greater  proportion  of  carbon  dioxide  produced  in  muscle 
during  activity  than  during  rest. 

During  rigor  mortis  there  is  also  an  increased  production  of  carbon  dioxide. 

Second,  muscle  during  rest  produces  nitrogenous  crystallizable  substances, 
such  as  creatin,  from  the  metabolism  which  is  constantly  going  on  in  it  during 
life;  in  addition  there  are  formed,  in  all  probability,  sarcolactic  acid  and 
other  non-nitrogenous  matters. 

During  activity  the  nitrogenous  substances,  such  as  creatin,  undergo 
very  slight,  if  any,  increase — about  the  amount  produced  during  rest — but 
the  sarcolactic  acid  is  distinctly  increased;  sugar  (glucose)  is  also  increased, 
whereas  the  glycogen  is  diminished. 

During  rigor  mortis  the  sarcolactic  acid  is  increased,  and  in  addition 
myosin  is  formed. 

From  these  data  it  is  assumed  that  the  processes  which  take  place  in 
resting  and  active  muscles  are  somewhat  different,  at  any  rate  in  degree. 
From  actively  contracting  muscle,  also,  there  are  obtained  an  increased 
amount  of  heat  and  mechanical  work;  potential  energy  is  converted  into 
kinetic  energy. 

Many  theories  have  been  proposed  to  explain  the  facts  of  muscular  energy. 
It  has  been  suggested  by  Herman  that  muscular  activity  depends  upon  the 
splitting  up  and  subsequent  re-formation  of  a  complex  nitrogenous  body, 
called  by  him  Inogen.  When  this  body  so  splits  up  there  result  from  its 
decomposition  carbon  dioxide,  sarcolactic  acid,  and  a  gelatino-albuminous 
body.  Of  these  the  carbon  dioxide  is  carried  away  by  the  blood  stream;  the 
albuminous  substance  and  possibly  the  acid,  at  any  rate  in  part,  go  to  re- 
form the  inogen.  The  other  materials  of  which  the  inogen  is  formed  are 
supplied  by  the  blood;  of  these  materials  we  know  that  some  carbohydrate 
substance  and  oxygen  form  a  part.  The  decomposition,  although  taking 
place  in  resting  muscle,  reaches  a  climax  in  active  muscle,  but  in  that  con- 
dition the  destruction  of  inogen  largely  exceeds  restoration,  and  so  there  must 
be  a  limit  to  muscular  activity.  But  this  is  net  the  only  change  going  on  in 
muscle,  there  are  others  which  affect  the  nitrogenous  elements  of  the  tissue, 
and  from  them  result  the  nitrogenous  bodies  of  which  creatin  is  the  chief; 
these  changes  may  be  unusually  large  during  severe  exercise. 

It  has  been  further  suggested  as  myosin  is  undoubtedly  formed  in  rigor 
mortis  when  the  muscle  becomes  acid  and  gives  off  carbon  dioxide,  and  since 
myosin  is  formed  also  when  muscle  contracts,  that  the  phenomenon  of 
contraction  is  a  condition  akin  to  partial  death.  The  electrical  reactions 
appear  to  justify  this;  both  contracted  and  dead  muscle  are  negative  to 
living  muscle  when  at  rest.  What  happens  to  the  myosin  which  is  formed 
when  muscle  contracts,  if  this  view  be  the  correct  one,  is  unknown.  Halli- 
burton suggests  that  the  myosin,  which  can  be  made  to  clot  and  unclot  easily 
enough  outside  the  body,  is  able  to  do  the  same  thing  in  the  body.     It  is  pos- 


CONTRACTION    IN    INVOLUNTARY    MUSCLE    AND    IN    CILIA         465 

sible  that  the  clotting  of  myosinogen  which  is  supposed  to  occur  during  con- 
traction is  not  of  the  same  intensity  or  extent  as  that  which  occurs  post  mortem. 
The  relation  of  the  hypothetical  inogen  to  the  rest  of  the  muscle  fiber  is  unde- 
termined. It  may  be  that  the  inogen  is  formed  by  the  activity  of  the  muscle- 
protoplasm  and  stored  up  within  itself,  and  that  during  rest  of  muscle  it  is 
gradually  used  up,  whereas  in  activity  it  is  suddenly  and  explosively  decom- 
posed. In  the  rest  of  the  fiber  the  nitrogenous  metabolism  continues  much 
the  same  during  activity. 

THE   TYPE    OF    CONTRACTION    IN   INVOLUNTARY 
MUSCLE   AND    IN   CILIA. 

Cardiac  Muscle.  Some  detail  concerning  the  action  of  cardiac  mus- 
cle has  already  been  given  in  connection  with  the  chapter  on  Circulation. 
As  compared  with  the  activity  of  skeletal  muscle,  cardiac  muscle  differs 
most  strikingly  in  that  it  is  automatic.  A  strip  of  heart  muscle  taken  from 
any  part  of  the  heart,  under  proper  conditions,  gives  off  a  series  of  contrac- 
tions, whether  it  receives  any  special  stimulus  or  not,  whereas  we  have  just 
found  that  skeletal  muscle  under  similar  conditions  remains  quiet  unless  stimu- 
lated in  some  special  way.  The  fibers  of  skeletal  muscle  are  more  or  less 
physiologically  isolated  from  each  other,  and  one  fiber  may  contract  without 
involving  contractions  of  the  others.  Cardiac  muscle,  on  the  other  hand, 
when  stimulated  at  any  point  conducts  the  change  produced  throughout  the 
continuity  of  the  mass.  Cardiac  muscle  contractions  are  influenced  by 
tension,  temperature,  fatigue,  etc.,  apparently,  in  the  same  way  as  skeletal 
muscle. 

When  the  contraction  occurs  it  is  always  maximal.  The  actual  am- 
plitude of  the  contraction  is  dependent  on  the  condition  of  nutrition  of  the 
cardiac  muscle.  If  the  contractions  are  at  a  rapid  rate  they  will  be  relatively 
of  less  amplitude.  If  an  extra  contraction  is  induced  in  an  automatic  series, 
so  that  the  interval  between  two  contractions  is  similar,  then  the  amplitude 
will  be  correspondingly  reduced.  Such  an  extra  contraction  is  followed  by 
a  delayed  automatic  contraction,  the  phenomenon  of  compensatory  pause. 
The  contractions  in  cardiac  muscle  are  simple  contractions.  In  fact,  it  is  said 
to  be  impossible  to  produce  a  tetanus  except  in  certain  invertebrate  hearts. 
This  possibility  depends  upon  the  fact  that  during  the  time  of  a  single  contrac- 
tion there  is  a  certain  interval  between  the  beginning  and  the  crest  of  the  con- 
traction, figure  174,  in  which  the  heart  muscle  is  not  irritable.  This  is  known 
as  the  refractory  phase. 

The  duration  of  the  contraction  of  heart  muscle  is  much  greater  than 
the  contraction  of  skeletal  muscle.  The  total  time  of  a  contraction  in  a  frog's 
gastrocnemius  is  0.1  of  a  second,  while  the  time  of  a  contraction  of  the  ven- 
tricle in  the  same  animal  is  at  least  0.7  to  0.8  of  a  second.  In  the  terrapin's 
30 


4G6 


MUSCLE-NERVE     PHYSIOLOGY 


cardiac  muscle  the  time  of  a  contraction  is  over  a  second,  but  in  the  warm- 
blooded cardiac  muscle  the  time  is  shorter,  perhaps  from  0.4  to  0.5  of  a 
second  for  the  human  ventricular  muscle. 

Smooth  Muscle.  The  physiology  of  smooth  muscle  has  been  given 
to  some  extent  in  previous  chapters,  particularly  in  connection  with  the  move- 
ments of  the  stomach  and  intestines.  As  compared  with  skeletal  and  cardiac 
muscle  it  is  a  much  more  slowly  acting  contractile  tissue.  Isolated  strips  of 
smooth  muscle,  as  a  rule,  contract  only  when  stimulated,  though  preparations 
of  certain  tissues,  like  the  stomach  muscle  of  the  frog,  give  off  rhythmic  con- 
tractions occasionally.  In  this  regard  smooth  muscle  stands  intermediate 
between  skeletal  and  cardiac  muscle ;  the  former  is  normally  never  automatic, 
the  latter  always. 

Smooth  muscle  requires  a  different  type  of  stimulus  to  produce  contraction; 
the  stimulus  must  be  more  prolonged  and  more  intense.     For  example, 


■_-;(/. 


:.ff-J 


Fig.  333- — Contraction  Area  in  Smooth  Muscle.  A,  Showing  the  contraction  nodes  of  the 
fibers,  the  deep  staining  of  the  nodes,  the  condensation  of  surrounding  connective  tissue;  B, 
diagrammatic,  showing  the  thickening  of  the  longitudinal  fibrilke.  Intestine  of  dog.  (Unpub- 
lished figure  by  Caroline  McGill.) 


smooth  muscle  is  not  readily  responsive  to  induction  currents  of  short  duration, 
but  is  readily  stimulated  by  galvanic  currents  or  induction  currents  of  longer 
duration.     The  stimulus  must  be  applied  through  a  longer  interval  of  time. 


CHANGES     DURING     THE     CONTRACTION     OF    SMOOTH     MUSCLE       4G7 

Preparations  of  the  stomach  muscle  can  scarcely  be  made  to  contract  by  a 
single  induction  current,  no  matter  how  intense.  Such  muscle  in  the  body  is 
always  associated  with  the  local  nervous  apparatus  which  plays  an  indeter- 
minate part  in  its  activity. 

The  ureters  and  gall-bladder  are  the  parts  most  difficult  to  excite  by  stimuli ; 
they  do  not  act  at  all  till  the  stimulus  has  been  long  applied,  and  then  con- 
tract feebly  and  to  a  small  extent.  The  contractions  of  the  cecum  and  stomach 
are  quicker,  and  still  quicker  those  of  the  iris  and  of  the  urinary  bladder. 
The  contractions  of  the  small  and  large  intestines,  of  the  vas  deferens,  and 
of  the  pregnant  uterus,  are  yet  more  regular  and  more  sustained. 

Changes  During  the  Contraction  of  Smooth  Muscle.  The  dura- 
tion as  well  as  type  of  contraction  in  smooth  muscle  is  very  markedly  differ- 
ent  from  that  of  voluntary  muscle.     A  contraction  in  smooth  muscle  is 


Fig.  334. — Enlarged  Detailed  Drawing  of  the  Nucleus  of  Smooth  Muscle  in  the  Relaxed  and 
in  the  Contracted  State.  Intestine  of  Necturus.  Zeiss  obj.  2,  oc.  8.  (Unpublished  figure  by  Caro- 
line McGi!!.) 

characterized  by  a  very  long  latent  period,  a  slowly  developed  contraction 
phase,  and  an  extremely  delayed  relaxation,  figure  355.  The  amount  and 
duration  of  the  contractions  are  dependent  upon  the  strength  and  duration  of 
the  stimulus,  though  the  curve  of  contraction  itself  does  not  in  other  respects 
differ  sharply  from  the  type  of  curve  of  the  simple  muscle  contraction. 

Owing  to  the  apparently  different  structural  type  of  smooth  muscle,  es- 
pecial interest  attaches  to  the  changes  which  occur  during  its  contraction. 
Caroline  McGill  has  recently  re-examined  the  histological  structure  and  in- 
vestigated the  function  of  this  type  of  muscle,  and  we  are  able  to  present  a 
figure  showing  the  changes.  The  longitudinal  fibrillae,  which  are  readily 
stained  with  iron  hematoxylin,  show  distinct  shortening  and  thickening  at  the 


468  MUSCLE-NERVE    PHYSIOLOGY 

nodes  of  contraction  of  the  muscle,  figure  333,  B.  The  whole  fiber  is  thick- 
ened at  the  contraction  nodes  and  stains  very  readily  and  usually  uniformly. 
However,  by  certain  stains  the  fibrillae  can  be  traced  through  the  node.  The 
node  is  an  apparent  area  of  chemical  differentiation.  There  is  a  marked  con- 
densation of  the  intermuscular  fibrous  tissue,  which  is  doubtless  purely  a 
passive  phenomenon.  The  most  striking  change  during  contractions  is 
observed  in  the  nucleus,  figure  333,  A,  and  figure  334.  The  nucleus  during 
rest  is  a  long  slender  oval  or  spindle  with  a  general  chromatic  network. 
"  During  contraction,  the  smooth  muscle  nuclei  shorten  and  thicken  by  an 
active  process.  The  chromatin  collects,  chiefly  at  the  two  ends  of  the 
nucleus,  leaving  a  relatively  clear  area  in  the  center." 

Ciliary  Motion.  Ciliary  motion,  which  is  closely  allied  to  ameboid 
and  muscular  motion,  is  alike  independent  of  the  will,  of  the  direct  influ- 
ence of  the  nervous  system,  and  of  muscular  contraction.  It  may  continue 
for  several  hours  after  death,  or  removal  of  the  ciliated  tissue,  provided  the 
portion  of  tissue  under  examination  be  kept  moist.  Its  independence  of  the 
nervous  system  is  shown  also  in  its  occurrence  in  the  lowest  invertebrate 
animals  which  are  apparently  unprovided  with  anything  analogous  to  a 
nervous  system,  and  in  its  persistence  when  the  ciliated  cells  are  completely 
separated  from  each  other  by  teasing  out  in  serum  or  other  physiological 
solution.  The  vapor  of  chloroform  arrests  the  motion;  but  it  is  renewed 
on  the  discontinuance  of  the  application  of  the  anesthetic.  The  movement 
ceases  when  the  cilia  are  deprived  of  oxygen  (although  it  may  continue  for 
a  time  in  the  absence  of  free  oxygen)  but  is  revived  on  the  admission  of  this 
gas.  Carbon  dioxide  also  stops  the  movement.  The  contact  of  various 
substances,  e.g.,  bile,  strong  acids,  and  alkalies,  will  stop  the  motion  altogether; 
but  this  depends  chiefly  on  destruction  of  the  delicate  substance  of  which  the 
cilia  are  composed.  Temperatures  above  450  C.  and  below  o°  C.  stop  the 
movement,  whereas  moderate  heat  and  faintly  alkaline  solutions  are  favorable 
to  the  action  and  revive  the  movement  after  temporary  cessation.  The  exact 
explanation  of  ciliary  movement  is  not  known.  Whatever  may  be  the  exact 
explanation,  the  movement  must  depend  upon  some  changes  going  on  in  the 
cells  of  which  the  cilia  are  a  part  and  not  on  changes  limited  to  the  cilia 
themselves,  since,  when  the  latter  are  cut  off  from  the  cell  the  movement 
ceases,  and  when  severed  so  that  portions  of  the  cilia  are  left  attached  to  the 
cell,  the  attached  and  not  the  severed  portions  continue  the  movement.  Ciliary 
contraction  is  to  be  regarded  as  a  type  of  motor  activity  carried  out  in  a  spe- 
cialized form  of  motor  apparatus.  The  changes  going  on  in  the  cell  must  be 
classed  with  similar  changes  in  heart  or  skeletal  muscle.  Ciliary  tissue  is 
like  cardiac  in  at  least  two  characteristics:  the  cells  are  capable  of  conducting 
a  stimulus  from  cell  to  cell,  and  ciliary  activity  is  automatic.  As  a  special 
illustration  of  cilia-like  action  may  be  mentioned  the  motion  of  spermatozoa, 
which  are  cells  with  a  single  cilium. 


THE     FUNCTION    OF     NERVE     FIBER  469 


THE   FUNCTION   OF   NERVE    FIBER. 

The  Nerve  Impulse.  The  motor  nerve  fibers  of  the  muscle-nerve 
preparation  are  of  the  medullated  type  described  on  page  64.  But  the  es- 
sential structure,  possessed  by  all  fibers,  is  the  axis  cylinder.  The  peculiar 
function  of  the  nerve  fiber,  i.e.,  of  the  axis  cylinder,  is  its  power  to  conduct 
a  physiological  change  along  its  extent,  a  phenomenon  known  as  a  nerve 
impulse.  A  normal  nerve  impulse  in  a  motor  nerve  has  its  origin  in  the  motor 
cell  of  the  central  nervous  system  of  which  the  fiber  is  an  outgrowth.  The 
manner  in  which  such  discharge  from  the  cell  takes  place  will  be  discussed 
later.  But  nerve  impulses  may  be  aroused  by  various  artificial  means,  they 
are  influenced  by  certain  conditions  in  the  environment,  and  possess  certain 
other  properties  that  may  be  discussed  at  this  point. 

Nerve  Stimuli.  Nerve  fibers  like  skeletal  muscle  require  stimu- 
lation before  they  can  manifest  any  of  their  properties,  since  they  have  no 
power  of  themselves  of  originating  nerve  impulses.  The  stimuli  which  are 
capable  of  exciting  nerves  to  action  are,  as  in  the  case  of  muscle,  very  diverse. 
The  mechanical,  chemical,  thermal,  and  electrical  stimuli  which  may  be  used 
in  the  case  of  muscles  are  also,  with  certain  differences  in  the  methods  em- 
ployed, efficacious  in  stimulating  the  nerve.  The  chemical  stimuli  are  chiefly 
these:  withdrawal  of  water  as  by  drying;  strong  solutions  of  neutral  salts  of 
potassium,  sodium,  etc.;  free  inorganic  acids,  except  phosphoric;  and  some 
organic  acids.  The  electrical  stimuli  employed  are  the  induction  and  con- 
tinuous currents  concerning  which  the  observations  in  reference  to  muscular 
irritability  should  be  consulted.  Galvanic  currents  stimulate  nerves  only  at 
the  moment  of  turning  on  the  current  and  of  turning  it  off.  Weaker  electrical 
stimuli  will  excite  nerves  than  will  excite  muscles;  the  nerve  impulse  appears 
to  gain  strength  as  it  descends,  and  a  weaker  stimulus  applied  far  from  the 
muscle  will  have  the  same  effect  as  a  slightly  stronger  one  applied  to  the  nerve 
near  the  muscle. 

Characteristics  of  the  Nerve  Impulse.  When  a  nerve  impulse  is 
aroused  in  a  motor  nerve,  as  by  stimulating  a  nerve  in  its  course  by  an  induced 
current  of  medium  strength,  it  is  propagated  along  the  axis  cylinder  to  the 
muscle  where  it  arouses  a  contraction  of  the  muscle  fiber.  In  the  contraction 
of  the  muscle  we  have  indirect  but  conclusive  evidence  of  the  passage  of  the 
nerve  impulse,  for  it  can  be  readily  proven  that  the  electrical  current  does 
not  escape  to  the  muscle.  In  this  instance  it  can  be  shown  that  there  is  a 
nerve  impulse  passing  from  the  point  of  stimulation  in  the  direction  away 
from  the  muscle;  i.e.,  the  artificially  aroused  nerve  impulse  passes  over  the 
entire  extent  of  the  fiber  stimulated.  In  fact,  a  nerve  impulse  is  known  to 
travel  from  its  point  of  origin  over  the  entire  neurone  affected.  This  antidro- 
mal  nerve  impulse,  of  course,  does  not  exist  in  the  normal  case,  since  the  nor- 


470  MUSCLE-NERVF,     PHYSIOLOGY 

mal  nerve  impulse  arises  in  the  nerve-cell  body  and  passes  out  over  the  fiber 
from  its  origin  to  its  extremity. 

The  nerve  impulse  travels  over  the  nerve  fiber  with  a  velocity  that  was 
first  determined  by  Helmholtz.  He  found  that  in  the  sciatic  of  the  frog  the 
nerve  impulse  travels  at  the  rate  of  twenty-seven  meters  per  second.  The  rate 
has  been  measured  in  a  number  of  animals  and  varies  between  wide  limits. 
In  human  nerves  the  rate  is  variously  given,  but  thirty  meters  per  second 
may  be  taken  as  a  fair  average. 

The  presence  of  the  nerve  impulse  can  be  detected  by  the  action  current, 
which  exists  in  nerve  as  in  muscle  (see  page  451  for  methods  of  detecting 
the  action  current). 

Rheoscopic  Frog.  The  action  current  may  be  demonstrated  by  means  of  the  follow- 
ing experiment: 

The  muscle  current  produced  by  stimulating  the  nerve  of  one  muscle-nerve  preparation 
may  be  used  to  stimulate  the  nerve  of  a  second  muscle-nerve  preparation.  The  hindleg 
of  a  frog  with  the  nerve  going  to  the  gastrocnemius  cut  long  is  placed  upon  a  glass  plate 
and  arranged  in  such  way  that  its  nerve  touches  in  two  places  the  gastrocnemius  muscle, 
exposed  but  preserved  in  situ  in  the  opposite  thigh  of  the  frog.  The  electrodes  from  an 
induction  coil  are  placed  behind  the  sciatic  nerve  of  the  second  preparation,  high  up. 
On  stimulating  it  with  a  single  induction  shock,  the  muscles  not  only  of  the  same  leg  are 
found  to  undergo  a  twitch,  but  also  those  of  the  first  preparation,  although  this  is  not  near 
the  electrodes.  The  stimulation  cannot  be  due  to  an  escape  of  the  stimulating  current 
into  the  first  nerve,  but  is  due  to  the  action  current  of  the  second  muscle.  This  experi- 
ment is  known  under  the  name  of  the  rheoscopic  jrog. 

When  the  nerve  impulse  is  studied  by  means  of  the  action  current  it  is 
found  that  a  nerve  impulse  can  be  aroused  by  a  weaker  stimulus  than  is  re- 
quired to  produce  a  minimal  contraction  of  a  muscle.  The  response  of  the 
nerve  to  graduated  strengths  of  the  stimulus  is  increased  very  rapidly  with 
slight  increase  of  strength  of  the  stimulus,  the  augmentation  extending  through 
a  somewhat  greater  range  than  for  muscle.  If  the  stimulus  is  still  further  in- 
creased there  is  only  slight  increase  of  the  resulting  nerve  impulse. 

Fatigue  of  Nerve  Fiber.  Many  efforts  have  been  made  to  dis- 
cover evidences  of  fatigue  of  nerve  fiber,  with  practically  complete  negative 
results.  A  difficulty  has  been  to  secure  means  of  measuring  change  in  intensity 
of  the  nerve  impulse.  The  muscle  quickly  fatigues  so  that  the  character  of 
the  muscle  response  cannot  be  taken  when  measured  in  the  ordinary  way. 
An  effective  method  used  by  Howell,  Budgett,  and  Leonard  consists  in  cooling 
a  segment  of  nerve  to  suspend  its  conductivity,  during  stimulation  of  the  free 
end;  and  periodically  warming  up  the  cooled  segment  of  nerve  to  test  the 
strength  of  nerve  impulse  passing  through  it  to  the  unfatigued  muscle  beyond. 
By  this  and  other  methods  it  has  been  found  that  a  motor  nerve  is  not  fatigued 
by  at  least  ten  hours'  continuous  stimulation  with  induction  currents. 

One  must  hesitate  to  draw  the  conclusion,  however,  that  the  nerve  fiber 
conducts  the  nerve  impulse  without  loss  of  energy.  The  fiber  can  be  anesthe- 
tized, it  responds  to  temperature  changes,  and  gives  other  evidences  of  sus- 


THE    EFFECTS     OF     BATTERY    CURRENTS     ON    NERVE-FIBER  471 

ceptibility  to  conditions  which  influence  metabolism  in  other  forms  of  proto- 
plasm. Perhaps  the  nerve  fiber  is  capable  of  repairing  its  wastes  as  rapidly 
as  they  occur. 

The  Effects  of  Battery  Currents  on  Nerve  Fiber.  Galvanic  currents 
influence  nerves  in  ways  that  call  for  special  discussion.  A  constant  cur- 
rent, say  from  a  Daniell  battery,  can  be  introduced  into  the  nerve  of  a 
muscle-nerve  preparation  by  means  of  a  pair  of  non-polarizable  electrodes, 
figure  3  23,  and  a  convenient  key  arranged  for  turning  the  current  on  or  off  the 
nerve.  It  will  be  found  that  with  a  current  of  moderate  strength  there  will  be  a 
contraction  of  the  muscle,  both  at  the  closing  and  the  opening  of  the  key  (called 
respectively  making  and  breaking  contractions),  but  that  during  the  interval 
between  these  two  events  the  muscle  remains  flaccid,  provided  the  battery  cur- 
rent continues  of  constant  intensity.  If  the  current  be  a  very  weak  or  a  very 
strong  one,  the  effect  is  not  quite  the  same;  one  or  the  other  of  the  contractions 
may  be  absent.  Which  of  these  contractions  is  absent  depends  upon  another 
circumstance,  viz.,  the  direction  of  the  current.  The  direction  of  the  current 
may  be  ascending  or  descending:  If  ascending,  the  anode  or  positive  pole  is 
nearer  the  muscle  than  the  cathode  or  negative  pole,  and  the  current  to  return 
to  the  battery  has  to  pass  up  the  nerve;  if  descending,  the  position  of  the  elec- 
trodes is  reversed.  It  will  be  necessary  before  considering  this  question 
further  to  return  to  the  apparent  want  of  effect  of  the  constant  current  during 
the  interval  between  the  make  and  the  break  contraction.  To  all  appear- 
ances no  change  is  produced,  but  in  reality  a  very  important  alteration  of 
the  irritability  and  conductivity  is  brought  about  in  the  nerve  by  the  passage 
of  this  constant  or  polarizing  current. 

A  second  way  of  showing  the  effect  of  the  polarizing  current  is  by  stimu- 
lating the  nerve  by  a  pair  of  electrodes  from  an  induction  coil,  while  the  polar- 
izing current  from  the  battery  is  flowing  through  the  nerve.  If  the  strength  of 
stimulus  required  in  order  that  a  minimum  contraction  be  obtained  by  the 
induction  shock  before  the  polarizing  current  is  applied,  and  the  secondary 
coil  be  removed  slightly  further  from  the  primary,  the  induction  current 
cannot  now  produce  a  contraction.  If  now  the  polarizing  current  be  sent  in  a 
descending  direction,  that  is  to  say,  with  the  cathode  nearest  the  muscle,  and 
the  induction  current  which  was  before  insufficient  be  applied  between  the 
cathode  and  the  muscle,  it  will  now  prove  sufficient  to  cause  a  contraction. 
This  indicates  that  with  a  descending  current  the  irritability  of  the  nerve  is 
increased  at  the  cathode.  If  instead  of  applying  the  induction  electrodes 
below  the  polarizing  electrodes,  they  are  applied  above  them,  the  irritability  of 
the  nerve  is  found  to  be  decreased.  If  the  polarizing  current  is  reversed,  i.e., 
made  ascending,  then  the  condition  of  irritability  of  the  nerve  is  reversed. 
Both  methods  show  that  the  polarization  consists  in  an  increase  in  irritability 
at  the  cathode,  called  catelcctrotonus,  and  a  decrease  at  the  anode  called 
anelectrotonus.     The  total  change  is  called  by  the  term  electrotonus.     As  there 


472 


MUSCLE-NERVE    PHYSIOLOGY 


is  between  the  electrodes  both  an  increase  and  a  decrease  of  irritability  on  the 
passage  of  a  polarizing  current,  it  is  evident  that  there  must  be  a  neutral  point 
where  there  is  neither  increase  nor  decrease  of  irritability.  The  position  of  this 
neutral  point  is  found  to  vary  with  the  intensity  of  the  polarizing  current;  when 
the  current  is  weak  the  point  is  nearer  the  anode,  when  strong  nearer  the 


-<^ss 


.""» 


Fig.  335. — Diagram  Illustrating  the  Effects  of  Various  Intensities  of  the  Polarizing  Currents. 
n,  n',  Nerve;  a,  anode;  k,  cathode;  the  curves  above  indicate  increase,  and  those  below  decrease 
of  irritability,  and  when  the  current  is  small  the  increase  and  decrease  are  both  small,  with  the 
neutral  point  near  a,  and  so  on  as  the  current  is  increased  in  strength. 

cathode,  figure  335.  When  a  constant  current  passes  into  a  nerve,  therefore,  if  a 
contraction  result,  it  may  be  assumed  that  it  is  due  to  the  increased  irritability 
produced  in  the  neighborhood  of  the  cathode,  but  the  breaking  contraction 
must  be  produced  by  a  rise  in  irritability  from  a  lowered  state  to  the  normal 
in  the  neighborhood  of  the  anode. 

The  contractions  produced  in  the  muscle  of  a  muscle-nerve  preparation 
by  a  constant  current  have  been  arranged  in  a  table  which  is  known  as  Pfluger's 
Law  of  Contractions.  It  is  really  only  a  statement  as  to  when  a  contrac- 
tion may  be  expected: 


Descending  Current. 

Ascending 

Current. 

Strength  of  Current  Used. 

Make. 

Break. 

Make. 

Break. 

Yes 
Yes 
Yes 
Yes 

No 
No 
Yes 

No 

No 
Yes 

Yes 
No 

No 

Weak 

No 

Yes 

Strong 

Yes 

During  the  passage  of  a  constant  current  through  a  nerve  and  immediately 
after  its  cessation,  there  is  a  change  in  the  conductivity  as  well  as  of  the  irri- 
tability of  the  nerve  at  the  anode  and  cathode,  respectively.  During  the  pas- 
sage of  the  current,  the  conductivity  is  increased  at  the  cathode  and  decreased 
at  the  anode.  After  the  passage  of  the  current,  the  effect  is  reversed.  With 
strong  currents  the  area  of  decreased  conductivity  may  be  sufficient  to  act  as  a 
block,  preventing  the  passage  of  impulses  over  it. 


EFFECT    OF     BATTERY    CURRENTS    ON    DEEP-SEATED    NERVES      473 

The  foregoing  statements  concerning  the  changes  produced  in  a  nerve 
by  the  passage  of  a  constant  current  may  be  briefly  summarized  as  follows: 

I.  A  nerve  is  more  irritable  to  the  closing  of  a  constant  current  than  it  is  to 
the  opening  of  a  constant  current. 

II.  During  the  passage  of  the  current  through  the  nerve,  both  its  irrita- 
bility and  conductivity  are  increased  at  the  cathode  and  decreased  at  the  anode. 

III.  After  the  passage  of  the  current,  the  irritability  and  conductivity  are 
both  decreased  at  the  cathode  and  increased  at  the  anode. 

The  Effect  of  Battery  Currents  on  Deep-Seated  Nerves.  The  follow- 
ing account  is  condensed  from  Lombard  in  "An  American  Text-book  of 
Physiology." 

As  an  electric  current  cannot  be  applied  to  living  human  nerves  directly, 
it  is  applied  to  the  skin  along  the  course  of  the  nerve.  The  current  passes 
from  the  anode  or  positive  pole  through  the  skin,  and  spreads  out  in  the 
tissues  much  as  the  bristles  of  a  brush;  it  then  gradually  concentrates  and 
leaves  the  skin  at  the  cathode  or  negative  pole. 

In  addition  to  the  physical  anode  and  cathode  of  the  battery,  there  are  what 
are  called  physiological  anodes  and  cathodes.  There  is  a  physiological  anode 
at  every  point  where  the  current  enters  a  nerve,  and  a  physiological  cathode 
at  every  point  where  it  leaves  it. 

Generally  when  the  cur-rent  is  applied  to  nerves  through  the  skin,  only  part 
of  it  flows  longitudinally  along  the  nerves;  most  of  it  passes  diagonally  through 


Fig.  33  5  A. — Diagram  of  Skin  and  Subjacent  Nerve.  A,  the  positive  electrode  or  physical 
anode;  B,  the  negative  electrode  or  physical  cathode.  Signs,  +  physiological  anodes;  signs- 
physiological  cathodes.     (After  Waller.) 


them  to  the  tissues  below.  Thus  it  happens  that  in  that  part  of  the  nerve 
beneath  either  the  physical  anode  or  cathode,  groups  of  physiological  anodes 
and  cathodes  are  found. 

The  contraction  which  occurs  when  the  current  is  closed  {closing  con- 
traction) represents  irritation  at  the  physiological  cathode,  while  the  opening 
contraction  represents  irritation  at  the  physiological  anode.  Since  there  are 
physiological  anodes  and  cathodes  beneath  each  electrode,  one  or  more  of 
four  conditions  may  arise: 

i.  Anodic  closing  contraction,  i.e.,  the  effect  of  the  change  developed  at 
the  physiological  cathode,  beneath  the  physical  anode  (positive  pole). 


474 


MUSCLE-NERVE     PHYSIOLOGY 


2.  Anodic  opening  contraction,  i.e.,  the  effect  of  the  change  developed  at 
the  physiological  anode,  beneath  the  physical  anode  (positive  pole). 

3.  Cathodic  closing  contraction,  i.e.,  the  effect  of  the  change  developed 
at  the  physiological  cathode,  beneath  the  physical  cathode  (negative  pole). 

4.  Cathodic  opening  contraction,  i.e.,  the  effect  of  the  change  developed 
at  the  physiological  anode,  beneath  the  physical  cathode  (negative  pole). 

The  following  abbreviations  of  these  contractions  are  used:  ACC,  AOC, 
KCC,  KOC. 

The  closing  contractions,  KCC  and  ACC,  are  stronger  than  the  opening 
contractions,  KOC  and  AOC.  Of  the  closing  contractions,  KCC  is  strong- 
er than  ACC.  Of  the  opening  contractions,  AOC  is  stronger  than  KOC. 
These  facts  are  also  shown  in  a  table  of  the  effects  of  gradually  increasing  the 
strength  of  the  current. 


Weak  Currents. 
KCC 


Medium  Currents. 

Strong  Currents 

KCC 

KCC 

ACC 

ACC 

AOC 

AOC 



KOC 

Sometimes  AOC  is  stronger  than  ACC. 

In  diseases  which  cause  degeneration  of  the  nerves  going  to  a  muscle, 
stimulation  causes  results  different  from  the  above,  and  we  get  what  is  known 
as  the  reaction  of  degeneration. 


r.  nervi  med.  m.  pron.  { 
tereti.  f 


r.  vol.  prof.  n.  ulnar.  . 

m.  palmar  brevls 
m.  abduc.  dig.  min.  I    "" 
m.  flex.  dig.  min.  (   " 
m.  oppon.  dig.  min.  —  . 

mm,  I'imbr. H.,III.,IV. t---\:'-:-* *  - 
c" "I  .j-  - 


m.  radial.  Intern, 
m.  flex.  dig.  prof. 

m.  flex.  dig.  sublim. 


m.  flex.  poll.  long, 
m.  medianus 

m.  abduc.  poll.  brev. 
m.  oppon.  poll, 
m.  flex.  poll.  brev. 
m.  adduc.  poll, 
m.  lumbrlc.  I. 


Fig.  336. — Figure  Showing  Motor  Points  in  the  Forearm. 


LOCOMOTION 


475 


The  intensity  of  the  anodic  or  cathodic  effects  is  increased  by  using  small 
electrodes,  and  decreased  by  electrodes  of  large  surface.  In  fact  in  practice 
it  is  usual  to  apply  the  indifferent  electrode  to  an  extended  surface,  thus  re- 
ducing its  effect  below  the  stimulating  intensity,  This  gives  only  one  active 
stimulating  electrode  and  is  known  as  the  method  of  unipolar  stimulation. 


SOME    SPECIAL   COORDINATED    MOTOR   ACTIVITIES. 
I.    LOCOMOTION. 

The  greater  number  of  the  more  important  muscular  actions  of  the  human 
body,  those,  namely,  which  are  arranged  harmoniously  so  as  to  subserve  some 
definite  purpose  in  the  animal  economy,  are  described  in  various  parts  of  this 
work  in  the  sections  which  treat  of  the  physiology  of  the  processes  by  which 
these  muscular  actions  are  resisted  or  carried  out.  There  are,  however,  some 
very  important  and  somewhat  complicated  muscular  acts  which  may  be  best 
described  in  this  place. 

Walking.  The  coordinated  movements  of  the  body  are  carried  out 
by  the  skeletal  muscles  acting  on  the  skeletal  elements  as  a  system  of  levers. 
Even  the  bones  of  the  skull  are  levers  in  so  far  as  their  relations  to  muscles 
are  concerned. 

Examples  of  the  three  orders  of  levers  in  the  Human  Body.  All  levers  have  been 
divided  into  three  kinds,  according  to  the  relative  position  of  the  power,  the  weight  to  be 
moved,  and  the  axis  of  motion  or  fulcrum.  In  a  lever  of  the  first  kind  the  power  is  at  one 
extremity  of  the  lever,  the  weight  at  the  other,  and  the  fulcrum  between  the  two.  If  the 
initial  letters  only  of  the  power,  weight,  and  fulcrum  be  used,  the  arrangement  will  stand 
thus:  P.  F.  W.  A  poker  as  ordinarily  used,  or  the  bar  in  figure  337,  may  be  cited  as  an 
example  of  this  variety  of  lever;    while,  as  an  instance  in  which  the  bones  of  the  human 


J? 


7T 


Fin.  337. 

skeleton  are  used  as  a  lever  of  the  same  kind,  may  be  mentioned  the  act  of  raising  the  body 
from  the  stooping  posture  by  means  of  the  hamstring  muscles  attached  to  the  tuberosity 
of  the  ischium  or  of  the  triceps  which  extends  the  forearm  by  action  at  the  elbow, 
figure  337. 


476 


MUSCLE-NERVE    PHYSIOLOGY 


In  a  lever  of  the  second  kind,  the  arrangement  is  thus:  P.  W.  F.;  and  this  leverage 
is  employed  in  the  act  of  raising  the  handles  of  a  wheelbarrow,  or  in  stretching  an  elastic 
band,  as  in  figure  338.  In  the  human  body  the  act  of  opening  the  mouth  by  depressing 
the  lower  jaw  is  an  example  of  the  same  kind — the  tension  of  the  muscles  which  close  the 
jaw  representing  the  weight,  figure  338. 

In  a  lever  of  the  third  kind  the  arrangement  is,  F.  P.  W.,  and  the  act  of  raising  a  pole, 
as  in  figure  339,  is  an  example.     In  the  human  body  there  are  numerous  examples  of  the 


Band 


Fig.  338. 

employment  of  this  kind  of  leverage.     The  act  of  bending  the  forearm  may  be  mentioned 
as  an  instance,  figure  339.     The  act  of  biting  is  another  example. 

At  the  ankle  we  have  examples  of  all  three  kinds  of  lever.  1st  kind — Extending  the 
foot.  3d  kind — Flexing  the  foot.  In  both  these  cases  the  foot  represents  the  weight: 
the  ankle  joint  the  fulcrum,  the  power  being  the  calf  muscles  in  the  first  case  and  the 
tibialis  anticus  in  the  second  case.     2d  kind — When  the  body  is  raised  on  tiptoe.     Here 


Fig.  339. 

the  tip  of  the  toe  is  the  fulcrum,  the  weight  of  the  body  acting  at  the  ankle  joint  the  weight, 
and  the  calf  muscles  the  power. 

In  the  human  body,  levers  are  most  frequently  used  at  a  disadvantage  as  regards  power, 
the  latter  being  sacrificed  for  the  sake  of  a  greater  range  of  motion.  Thus  in  the  diagrams 
of  the  first  and  third  kinds  it  is  evident  that  the  power  is  so  close  to  the  fulcrum  that  great 
force  must  be  exercised  in  order  to  produce  motion.  It  is  also  evident,  however,  from  the 
same  diagrams,  that  by  the  closeness  of  the  power  to  the  fulcrum  a  great  range  of  move- 
ment can  be  obtained  by  means  of  a  comparatively  slight  shortening  of  the  muscular  fibers. 


In  the  act  of  walking,  almost  every  voluntary  muscle  in  the  body  is  brought 
into  play,  either  directly  for  purposes  of  progression,  or  indirectly  for 
the  proper  balancing  of  the  head  and  trunk.     The  muscles  of  the  arms  are 


LOCOMOTION 


477 


least  concerned;  but  even  these  are  for  the  most  part  instinctively  in  action 
to  some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of  walking  are  those  of 
the  calf,  which,  by  pulling  up  the  heel,  pull  up  also  the  astragalus,  and  with  it, 
of  course,  the  whole  body,  the  weight  of  which  is  transmitted  through  the 
tibia  to  this  bone,  figure  340.  When  starting  to  walk,  say  with  the  left  leg, 
this  raising  of  the  body  is  not  entirely  dependent  on  the  muscles  of  the  left 
calf,  but  the  trunk  is  thrown  forward  in  such  a  way  that  it  would  fall  prostrate 
were  it  not  that  the  right  foot  is  brought  forward  and  planted  on  the  ground  to 
support  it.  Thus  the  muscles  of  the  left  calf  are  assisted  in  their  action  by 
those  muscles  on  the  front  of  the  trunk  and  legs  which,  by  their  contraction, 
pull  the  body  forward;  and,  of  course,  if  the  trunk  form  a  slanting  line,  with 
the  inclination  forward,  it  is  plain  that  when  the  heel  is  raised  by  the  calf 
muscles,  the  whole  body  will  be  raised,  and  pushed  obliquely  forward  and 


upward.  The  successive  acts  in  taking  the  first  step  in  walking  are  repre- 
sented in  figure  340,  1,  2,  3,  etc. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed  the  position  No.  3, 
it  is  time  that  the  right  leg  should  be  brought  forward  to  support  it  and 
prevent  it  from  falling  prostrate.  This  advance  of  the  right  leg  is  effected 
partly  by  its  mechanically  swinging  forward,  pendulum- wise,  and  partly  by 
muscular  action;  the  muscles  used  being — 1,  those  on  the  front  of  the 
thigh,  which  bend  the  thigh  forward  on  the  pelvis,  especially  the  rectus  femoris, 
with  the  psoas  and  the  iliacus;  2,  the  hamstring  muscles,  which  slightly  bend 
the  leg  on  the  thigh;  and,  3,  the  muscles  on  the  front  of  the  leg,  which  raise 
the  front  of  the  foot  and  toes,  and  so  prevent  the  latter  in  swinging  forward 
from  striking  the  ground. 

The  second  part  of  the  act  of  walking,  which  has  been  just  described,  is 
shown  in  the  diagram,  4,  figure  340. 

When  the  right  foot  has  reached  the  ground  the  action  of  the  left  leg  has  not 
ceased.  The  calf  muscles  of  the  latter  continue  to  act,  and,  by  pulling  up  the 
heel,  throw  the  body  still  more  forward  over  the  right  leg,  now  bearing  nearly 
the  whole  weight,  until  the  time  when  the  left  leg  should  again  swing  forward, 
and  the  left  foot  be  planted  on  the  ground  to  prevent  the  body  from  falling 


478 


MUSCLE-NERVE    PHYSIOLOGY 


prostrate.  As  at  first,  while  the  calf  muscles  of  one  leg  and  foot  are  preparing, 
so  to  speak,  to  push  the  body  forward  and  upward  from  behind  by  raising  the 
heel,  the  muscles  on  the  front  of  the  trunk  and  the  same  leg  (and  of  the  other  leg, 
except  when  it  is  swinging  forward  (are  helping  the  act  by  pulling  the  legs  and 
trunk,  so  as  to  made  them  incline  forward,  the  rotation  in  the  inclining  occur- 
ring mainly  at  the  ankle  joint.  Two  main  kinds  of  leverage,  are,  therefore, 
employed  in  the  act  of  walking,  and  if  this  idea  be  firmly  grasped,  the  details 
will  be  understood  with  comparative  ease.  One  kind  of  leverage  employed 
in  walking  is  essentially  the  same  with  that  employed  in  pulling  forward  the 
pole,  as  in  figure  339.  And  the  other,  less  exactly,  is  that  employed  in  raising 
the  handles  of  a  wheelbarrow.     Now,  supposing  the  lower  end  of  the  pole  to  be 


Fig.  341. 

placed  in  the  barrow,  we  should  have  a  very  rough  and  inelegant,  but  not 
altogether  bad  representation  of  the  two  main  levers  employed  in  the  act  of 
walking.  The  body  is  pulled  forward  by  the  muscles  in  front,  much  in  the 
same  way  that  the  pole  might  be  by  the  force  applied  at  p,  while  the  raising 
of  the  heel  and  pushing  forward  of  the  trunk  by  the  calf  muscles  are  roughly 
represented  on  raising  the  handles  of  the  barrow.  The  manner  in  which  these 
actions  are  performed  alternately  by  each  leg,  so  that  one  after  the  other  is 
swung  forward  to  support  the  trunk,  which  is  at  the  same  time  pushed  and 
pulled  forward  by  the  muscles  of  the  other,  may  be  gathered  from  the  previous 
description. 

There  is  one  more  thing  to  be  especially  noticed  in  the  act  of  walking.  In- 
asmuch as  the  body  is  being  constantly  supported  and  balanced  on  each  leg 
alternately,  and  therefore  on  only  one  at  the  same  moment,  it  is  evident  that 
there  must  be  some  provision  made  for  throwing  the  center  of  gravity  over  the 


RUNNING  479 

line  of  support  formed  by  the  bones  of  each  leg,  as,  in  its  turn,  it  supports  the 
weight  of  the  body.  This  may  be  done  in  various  ways,  and  the  manner  in 
which  it  is  effected  is  one  element  in  the  differences  which  exist  in  the  walk- 
ing of  different  people.  Thus  it  may  be  done  by  an  instinctive  slight  rotation 
of  the  pelvis  on  the  head  of  each  femur  in  turn,  in  such  a  manner  that  the  cen- 
ter of  gravity  of  the  body  shall  fall  over  the  foot  of  this  side.  Thus  when  the 
body  is  pushed  onward  and  upward  by  the  raising,  say,  of  the  right  heel,  as  in 
figure  340,  3,  the  pelvis  is  instinctively  by  various  muscles  made  to  rotate  on  the 
head  of  the  left  femur  at  the  acetabulum,  to  the  left  side,  so  that  the  weight 
may  fall  over  the  line  of  support  formed  by  the  left  leg  at  the  time  that  the 
right  leg  is  swinging  forward,  and  leaving  all  the  work  of  support  to  fall  on 
its  fellow.  Such  a  ''rocking"  movement  of  the  trunk  and  pelvis,  however,  is 
accompanied  by  a  movement  of  the  whole  trunk  and  leg  over  the  foot  which 
is  being  planted  on  the  ground,  figure  341,  the  action  being  accompanied  with 
a  compensatory  outward  movement  at  the  hip,  more  easily  appreciated  by 
looking  at  the  figure  (in  which  this  movement  is  shown  exaggerated)  than 
from  the  description. 

Thus  the  body  in  walking  is  continually  rising  and  swaying  alternately 
from  one  side  to  the  other,  as  its  center  of  gravity  has  to  be  brought  alternately 
over  one  or  the  other  leg;  and  the  curvatures  of  the  spine  are  altered  in  corre- 
spondence with  the  varying  position  of  the  weight  which  it  has  to  support.  The 
extent  to  which  the  body  is  raised  or  swayed  differs  much  in  different  people. 

In  walking,  one  foot  or  the  other  is  always  on  the  ground.  The  act  of  leap- 
ing or  jumping  consists  in  so  sudden  a  raising  of  the  heels  by  the  sharp  and 
strong  contraction  of  the  calf  muscles  that  the  body  is  jerked  off  the  ground. 
At  the  same  time  the  effect  is  much  increased  by  first  bending  the  thighs  on  the 
pelvis,  and  the  legs  on  the  thighs,  and  then  suddenly  straightening  out  the 
angles  thus  formed.  The  share  which  this  action  has  in  producing  the  effect 
may  be  easily  known  by  attempting  to  leap  in  the  upright  posture,  with  the 
legs  quite  straight. 

Running.  Running  is  performed  by  a  series  of  rapid  low  jumps  pro- 
duced by  each  leg  alternately;  so  that,  during  each  complete  muscular  act 
concerned,  there  is  a  moment  when  both  feet  are  off  the  ground. 

In  all  these  cases,  however,  the  description  of  the  manner  in  which  any 
given  effect  is  produced,  can  give  but  a  very  imperfect  idea  of  the  infinite 
number  of  combined  and  harmoniously  arranged  muscular  contractions  which 
are  necessary  for  even  the  simplest  acts  of  locomotion. 

II.  THE  PRODUCTION  OF  THE  VOICE. 

Before  commencing  the  consideration  of  the  Nervous  System  and  the 
special  Senses  it  will  be  convenient  to  consider  first  speech,  the  production  of 
the  human  voice,  and  the  physiology  of  the  larynx  as  a  muscular  apparatus. 


480  MUSCLE-NERVE     PHYSIOLOGY 

The  Larynx.  In  nearly  all  air-breathing  vertebrate  animals  there 
are  arrangements  for  the  production  of  sound,  or  voice,  in  some  parts  of  the 
respiratory  apparatus.  In  many  animals,  the  sound  admits  of  being  variously 
modified  and  altered  during  and  after  its  production;  and,  in  man,  one  such 
modification  occurring  in  obedience  to  dictates  of  the  cerebrum,  is  speech. 

It  has  been  proven  by  observations  on  living  subjects,  by  means  of  the 
laryngoscope,  as  well  as  by  experiments  on  the  larynx  taken  from  the  dead 
body,  that  the  sound  of  the  human  voice  is  the  result  of  the  vibration  of  the 
inferior  laryngeal  ligaments,  or  the  true  vocal  cords  which  bound  the  glottis, 
caused  by  currents  of  expired  air  impelled  over  their  edges.  If  a  free  opening 
exists  in  the  trachea,  the  sound  of  the  voice  ceases,  but  it  returns  if  the  opening 
is  closed.  An  opening  into  the  air-passages  above  the  glottis,  on  the  con- 
trary, does  not  prevent  the  voice  being  produced.  By  forcing  a  current  of 
air  through  the  larynx  in  the  dead  subject,  clear  vocal  sounds  are  elicited, 
though  the  epiglottis,  the  upper  ligaments  of  the  larynx  or  false  vocal  cords,  the 
ventricles  between  the  upper  ligaments  and  the  inferior  ligaments,  and  the  upper 
part  of  the  arytenoid  cartilages,  be  all  removed.  But  the  true  vocal  cords  must 
remain  entire  with  their  points  of  attachment,  and  be  kept  tense  and  so 
approximated  that  the  fissure  of  the  glottis  may  be  narrow. 

The  vocal  ligaments  or  cords,  therefore,  are  regarded  as  the  proper  organs 
for  the  production  of  vocal  sounds.  The  modifications  of  these  sounds  are 
effected,  as  will  be  presently  explained,  by  other  parts,  viz.,  by  the  tongue, 
teeth,  lips,  etc.  The  structure  of  the  vocal  cords  is  adapted  to  enable  them  to 
vibrate  like  tense  membranes,  for  they  are  essentially  composed  of  elastic  tissue; 
and  they  are  so  attached  to  the  cartilaginous  parts  of  the  larynx  that  their 
position  and  tension  can  be  variously  altered  by  the  contraction  of  the  muscles 
which  act  on  these  parts. 

Thus  it  will  be  seen  that  the  larynx  is  the  organ  of  voice.  It  may  be  said 
to  consist  essentially  of  the  two  vocal  cords  and  the  various  cartilaginous, 
muscular,  and  other  apparatus  by  means  of  which  not  only  can  the  aperture 
of  the  larynx  (rima  glottidis)  be  closed  against  the  entrance  and  exit  of  air 
to  or  from  the  lungs,  but  also  by  means  of  which  the  cords  themselves  can  be 
stretched  or  relaxed,  brought  together  and  separated  in  accordance  with  the 
conditions  that  may  be  necessary  for  the  air  in  passing  over  them  to  set  them 
vibrating  to  produce  the  various  sounds.  Their  action  in  respiration  has  been 
already  referred  to. 

Anatomy  of  the  Larynx.  The  principal  parts  entering  into  the  formation  of  the  larynx, 
figures  342  and  343,  are — the  thyroid  cartilage;  the  cricoid  cartilage;  the  two  arytenoid 
cartilages;  and  the  two  true  vocal  cords.  The  epiglottis,  figure  343,  has  but  little  to  do 
with  the  voice,  and  is  chiefly  useful  in  protecting  the  upper  part  of  the  larynx  from  the 
entrance  of  food  and  drink  in  deglutition.  The  false  vocal  cords  and  the  ventricle  of  the 
larynx,  which  is  a  space  between  the  false  and  the  true  cord  of  either  side,  need  be  only 
referred  to. 

Cartilages,     a,  The  thyroid  cartilage,  figure  342,  1  to  4,  does  not  form  a  complete  ring 


ANATOMY     OP    THE     LARYNX 


481 


around  the  larynx,  but  only  covers  the  front  portion,  b,  The  cricoid  cartilage,  figure  342, 
5,  6,  on  the  other  hand,  is  a  complete  ring;  the  back  part  of  the  ring  being  much  broader 
than  the  front.  On  the  top  of  this  broad  portion  of  the  cricoid  are,  c,  the  arytenoid  car- 
tilages, figure  342,  7,  the  connection  between  the  cricoid  below  and  arytenoid  cartilages 


Fig.  342. — Cartilages  of  the  Larynx  Seen  from  the  Front.  1  to  4,  Thyroid  cartilage;  1,  verti- 
cal ridge  or  pomum  Adami;  2,  right  ala;  3,  superior,  and  4,  inferior  cornu  of  the  right  side;  5,  6, 
cricoid  cartilage;  5,  inside  of  the  posterior  part;  6,  anterior  narrow  part  of  the  ring;  7,  arytenoid 
cartilages.      X  J. 

above  being  a  joint  with  synovial  membrane  and  ligaments,  the  latter  permitting  tolerably 
free  motion  between  them. 

Joints  and  Ligaments.  The  thyroid  cartilage  is  also  connected  with  the  cricoid,  not 
only  by  ligaments,  but  also  by  joints  with  synovial  membranes;  the  lower  comua  of  the 
thyroid  clasping  the  cricoid  between  them,  yet  not  so  tightly  but  that  the  thyroid  can  re- 


Xf£.  ArjftfeplglolL  e 


Cart1.  "Wrisfjergii 
Cart,  SantorinL 

Cart,  aryten. 
Trac.  rausctfl. 

!Eig»  crico-aryten.  --'"I 
JLfg,  ceratecrico.  post,  "sup, <t 

Cornuunfei'.— — 
J2g,  carafccrjm. joat^inf .  » — 

Cart,  trachea; 


ars  membra*. 


pIGi  343. — The  Larynx  as  Seen  From  Behind  after  Removal  of  the  Muscles.     The  cartilages  and 
ligaments  only  remain.      (Stoerk.) 

volve,  within  a  certain  range,  around  an  axis  passing  transversely  through  the  two  joints. 
The  vocal  cords  are  attached  behind  to  the  front  portion  of  the  base  of  the  arytenoid  car- 
tilages, and  in  front  to  the  re-entering  angle  at  the  back  part  of  the  thyroid;  it  is  evident, 
therefore,  that  all  movements  of  either  of  these  cartilages  must  produce  an  effect  on  them 
of  some  kind  or  other.  Inasmuch,  too,  as  the  arytenoid  cartilages  rest  on  the  top  of  the 
back  portion  of  the  cricoid  cartilage,  and  are  connected  with  it  by  capsular  and  other  liga- 
ments, all  movements  of  the  cricoid  cartilage  must  move  the  arytenoid  cartilages,  and  also 
produce  an  effect  on  the  vocal  cords. 
31 


482 


MUSCLE-NERVE     PHYSIOLOGY 


Intrinsic  Muscles.  The  intrinsic  muscles  of  the  larynx  are  so  connected  with  the 
laryngeal  cartilages  that  by  their  contraction  alterations  in  the  condition  of  the  vocal  cords 
and  glottis  are  produced.  They  are  usually  divided  into  four  classes  according  to  their 
action,  viz.,  into  abductors,  adductors,  sphincters,  and  tensors.  The  Abductors,  the  crico- 
arytenoidei,  widen  the  glottis,  by  separating  the  cords;  the  Adductors,  consisting  of  the 
thyro-ary-epiglottici,  the  arytenoideus  posticus  seu  transversus,  the  thyro-arytenoidei  externi, 


Fig.  344. — The  Cartilages  and  Ligaments  of  the  Larynx,  Viewed  from  the  Front,  a.  Epiglottis; 
b,  hyoid  bone;  c,  cartilago  tritica;  d,  thyro-hyoid  membrane;  e,  superior  cornu  of  thyroid  cartilage- 
j,  thyroid  notch;  g,  pomum  Adami;  /;,  crico-thyroid  membrane;  i,  inferior  cornu  of  thyroid  cartilage; 
f ,  cricoid  cartilage.      (Cunningham.) 

the  crico-arytenoideilaterales,  and  the  thyro-arytenoidei  inter ni,  approximate  the  vocal  cords, 
diminish  the  rima  glottidis,  and  act  generally  as  sphincters  and  supporters  of  the  glottis. 
Finally,  the  tensors  of  the  cords  put  the  cords  on  the  stretch,  with  or  without  elongating 
them;   the  tensors  are  the  crico-thyroidei  and  the  thyro-arytenoidei  inter  ni. 

The  attachments  and  the  action  of  the  muscles  will  be  readily  understood  from  the 
following  table.     All  the  muscles  are  in  pairs  except  the  arytenoideus  posticus. 


Table  of  the  several  Groups  of  the  Intrinsic  Muscles  of  the  Larynx  and  their 

Attachments. 


Group. 


Muscle. 


Attachments. 


Action. 


I. 

Abductors. 


Crico-aryte- 
noidei  pos- 
tici. 


This  pair  of  muscles  arises,  on  either 
side,  from  the  posterior  surface  of  the 
corresponding  half  of  the  cricoid  car- 
tilage. From  this  depression  their 
fibers  converge  on  either  side  upward 
and  outward  to  be  inserted  into  the 
outer  angle  of  the  base  of  the  ary- 
tenoid cartilages  behind  the  crico- 
arytenoidei  laterales. 


)raw  inward  and 
backward  the  out- 
er angle  of  ary- 
tenoid cartilages, 
and  so  rotate  out- 
ward the  processus 
vocalis  and  widen 
the  glottis. 


ANATOMY     OF    THE     LARYNX 


483 


Group. 


II.  and  III. 
Adductors 

and 
Sphincters. 


Muscle. 


In   three  lay- 
ers: 

Outer 
layer,  Thy- 
ro-ary- 
e  p  i  g lo  t - 
tici. 


Attachments. 


Action. 


Middle 
layer. 

i.  Aryte- 
n  o  i  d  e  u  s 
posticus. 

ii.  Thyro- 
ary  tenoi- 
d  e  i  e  x  - 
terni. 


hi.  Crico- 
arytenoi 
dei  late 
rales. 


A  pair  of  muscles.  Flat  and  narrow, 
which  arise  on  either  side  from  the 
processus  muscularis  of  the  arytenoid 
cartilage,  then  passing  upward  and  in- 
ward cross  one  another  in  the  middle 
line  to  be  inserted  into  the  upper  half 
of  the  lateral  border  of  the  opposite 
arytenoid  cartilage  and  the  posterior 
border  of  the  cartilage  of  Santorini. 
The  lower  fibers  run  forward  and 
downward  to  be  inserted  into  the 
thyroid  cartilage  near  the  commissure 
The  fibers  attached  to  the  cartilage  of 
Santorini  are  continued  forward  and 
upward  into  the  ary -epiglottic  fold. 

A  single  muscle.  Half-quadrilateral, 
attached  to  the  borders  of  the  ary 
tenoid  cartilages,  its  fibers  running 
horizontally  between  the  two. 

A  pair  of  muscles.  Each  of  which  con- 
sists of  three  chief  portions.  The 
lower  and  principal  fibers  arise  from 
the  lower  half  of  the  internal  surface 
of  the  thyroid  cartilage,  close  to  the 
angle,  and  from  the  fibrous  expansion 
of  the  crico-thyroid  ligament,  and  are 
inserted  into  the  lateral  border  of  the 
arytenoid  cartilage.  The  inner  fibers 
to  the  lower  half  of  this  border,  and 
the  outer  fibers  into  the  upper  half 
some  pass  to  the  cartilage  of  Wrisberg 
and  the  ary-epiglottic  fold. 

A  pair  of  muscles.  They  arise  on  either 
side  from  the  middle  third  of  the  up 
per  border  of  the  cricoid  cartilage  and 
are  inserted  into  the  whole  anterior 
margin  of  the  base  of  the  arytenoid 
cartilage.  Some  of  their  fibers  join 
the  thyroid -ary-epiglottici. 


Help  to  narrow  or 
close  the  rima 
glottidis. 


Draws  together  the 
arytenoid  carti- 
lages and  also  de- 
presses them. 
When  the  mus- 
cle is  paralyzed, 
the  i  n  t  e  r-c  a  r  t  i- 
laginous  part  of 
the  cords  cannot 
come  together. 


:.  Inner- 
most layer, 
Thyro-ar  y- 
tenoidei  in- 
tend. 


A  pair  of  muscles.  They  arise  on  either 
side,  internally  from  the  angle  of  the 
thyroid  cartilage,  internal  to  the  last 
described  muscle,  b.  iii.,  and  running 
parallel  to  and  in  the  substance  of  the 
vocal  cords  are  attached  posteriorly  to 
the  processus  vocalis  and  to  the  outer 
surface  of  the  arytenoid  cartilages. 


Approximate  the 
vocal  cords 
by  drawing  the 
processus  muscu- 
laris of  the  ary- 
tenoid cartilages 
forward  and 
downward  and  so 
rotate  the  pro- 
cessus vocalis  in- 
ward. 

Render  the  vocal 
cords  tense  and 
rotate  the  aryte- 
noid cartilages 
and  approximate 
the  processus  vo- 
calis. 


484 


MUSCLE-NERVE    PHYSIOLOGY 


Group. 


IV. 

Tensors. 


Muscle. 


Attachments. 


Crico  -thy- 
roidei. 


Thyro  -  ary- 
t  e  noi  dei 
interni. 


A  pair  of  fan-shaped  muscles  attached 
on  either  side  to  the  cricoid  cartilage 
below;  from  the  mesial  line  in  front 
for  nearly  one-half  of  its  lateral  cir 
cumference  backward  the  fibers  pass 
upward  and  outward  to  be  attached  to 
the  lower  border  of  the  thyroid  carti 
lage  and  to  the  front  border  of  its  lower 
cornea. 

The  most  posterior  part  is  almost  a  dis- 
tinct muscle  and  its  fibers  are  all  but 
horizontal:  sometimes  this  muscle  is 
described  as  consisting  of  two  layers, 
superficial  with  cortical  fibers,  deep 
with  oblique  fibers,  described  under 
Group  III. 


Action. 


The  thyroid  carti- 
lage being  fixed 
by  its  extrinsic 
muscles,  the 
front  of  the  cri- 
coid cartilage  is 
drawn  upward, 
and  its  back, 
with  the  aryte- 
noids attached, 
is  drawn  down. 
Hence  the  vocal 
cords  are  elon- 
gated a  n  t  e  r  o  - 
posteriorly  and 
put  upon  the 
stretch.  Paral- 

ysis of  these 
muscles  causes 
an  inability  to 
produce  high 
notes. 


Nerve  Supply.  The  sensory  filaments  of  the  superior  laryngeal  branch  of  the  vagus 
supply  the  epithelial  lining  of  the  larynx,  giving  it  that  acute  sensibility  by  which  the  glottis 
is  guarded  against  the  ingress  of  foreign  bodies,  or  of  irrespirable  gases.  The  contact  of 
these  stimulates  the  nerve  endings;  and  the  sensory  nerve  impulse  conveyed  to  the  medulla 
oblongata,  whether  accompanied  by  sensation  or  not,  arouses  motor  impulses  through 
the  filaments  of  the  recurrent  or  inferior  laryngeal  branch,  which  excite  contraction  of  the 
muscles  that  close  the  glottis.     Both  these  branches  of  the  vagi  cooperate  also  in  the  pro- 


Lig.  ary-epiglott. 

Cart.  Wrisbergii  _ 
Cart.  Santorini 


mm.  Aryten.  obliqu.   .-Jj 


m.  Cricoarytenoid,  post. 

Cornu  inferior 

Lig.  cerato-cric. 

Pars.  post.  inf.  membrani 
Pars,  cartilag. 


Fig.  345. — The  Larynx  as  Seen  from  Behind.     To  show  the  intrinsic  muscles 
posteriorly.      (Stoerk.) 


ANATOMY    OF    THE    LARYNX 


485 


duction  and  regulation  of  the  voice.  The  inferior  laryngeal  determines  the  degree  of 
contraction  of  the  muscles  that  vary  the  tension  of  the  vocal  cords,  and  the  superior  laryn- 
geal conveys  to  the  brain  the  sensation  which  indicates  the  state  of  contraction  of  these 
muscles.  Both  the  branches  co-operate  also  in  the  actions  of  the  larynx  in  the  ordinary 
slight  dilatation  and  contraction  of  the  glottis  in  the  acts  of  expiration  and  inspiration, 
more  evidently  in  the  acts  of  coughing  and  other  forcible  respiratory  movements. 

The  Laryngoscope.  This  is  an  instrument  employed  in  investigating  the  condition  of 
the  pharynx,  larynx,  and  trachea.  It  consists  of  a  large  concave  mirror  with  perforated 
center  and  of  a  smaller  mirror  fixed  in  a  long  handle.  In  use  the  patient  is  placed  in  a 
chair,  a  good  light  (argand  burner,  or  lamp)  is  arranged  on  one  side  of,  and  a  little  above 
his  head.     The  operator  fixes  the  concave  mirror  round  his  head  in  such  a  manner  that 


Fig.  346. — The  Parts  of  the  Laryngoscope. 

he  looks  through  the  central  aperture  with  one  eye.  He  then  seats  himself  opposite  the 
patient,  and  so  adjusts  the  position  of  the  mirror,  which  is  for  this  purpose  provided  with 
a  ball  and  socket  joint,  that  a  beam  of  fight  is  reflected  on  the  lips  of  the  patient. 

The  patient  is  now  directed  to  throw  his  head  slightly  backward,  and  to  open  his  mouth ; 
the  reflection  from  the  mirror  lights  up  the  cavity  of  the  mouth,  and  by  a  little  alteration  of 
the  distance  between  the  operator  and  the  patient  the  point  at  which  the  greatest  amount 
of  light  is  reflected  by  the  mirror — in  other  words  its  focal  length — is  readily  discovered. 
The  small  mirror  fixed  in  the  handle  is  then  warmed,  either  by  holding  it  over  the  lamp, 
or  by  putting  it  into  a  vessel  of  warm  water;  this  is  necessary  to  prevent  the  condensation  of 
breath  upon  its  surface.  The  degree  of  heat  is  regulated  by  applying  the  back  of  the  mirror 
to  the  hand  or  cheek,  when  it  should  feel  warm  without  being  painful. 

After  these  preliminaries  the  patient  is  directed  to  put  out  his  tongue,  which  is  held 
by  the  left  hand  of  the  operator  gently  but  firmly  against  the  lower  teeth  by  means  of 
a'handkerchief.  The  warm  mirror  is  passed  to  the  back  of  the  mouth,  until  it  rests  upon 
and  slightly  raises  the  base  of  the  uvula,  and  at  the  same  time  the  light  is  directed  upon 
it:  an  inverted  image  of  the  larynx  and  trachea  will  be  seen  in  the  mirror.  If  the  dorsum 
of  the  tongue  be  alone  seen,  the  handle  of  the  mirror  must  be  slightly  lowered  until  the 
larynx  comes  into  view;   care  should  be  taken,  however,  not  to  move  the  mirror  upon  the 


486 


MUSCLE-NERVE     PHYSIOLOGY 


uvula,  as  it  excites  retching.     The  observation  should  not  be  prolonged,  but  should  rather 
be  repeated  at  short  intervals. 

The  structures  seen  will  vary  somewhat  according  to  the  condition  of  the  parts  as  to 
inspiration,  expiration,  phonation,  etc.  They  are  the  following:  first,  and  apparently 
at  the  posterior  part,  the  base  of  the  tongue,  immediately  below  which  is  the  accurate  out- 
line of  the  epiglottis,  with  its  cushion  or  tubercle,  figure  348.  Then  are  seen  in  the  central 
line  the  true  vocal  cords,  white  and  shining  in  their  normal  condition.  In  the  inverted  image 
the  cords  are  closer  together  posteriorly.  Between  them  is  left  an  open  slit,  narrow  while 
a  high  note  is  being  sounded,  wide  during  a  deep  inspiration.  On  each  side  of  the  true 
vocal  cords,  and  on  a  higher  level,  are  the  false  vocal  cords.  Still  more  externally  than  the 
false  vocal  cords  is  the  aryteno-epiglottidean  fold,  in  which   are  situated  upon  each  side 


Fig.  347. — To  Show  the  Position  of  the  Operator  and  Patient  when  Using  the  Laryngoscope. 


three  small  elevations;  of  these  the  most  external  is  the  cartilage  of  Wrisberg,  the  interme- 
diate is  the  cartilage  of  Santorini,  while  in  front  and  somewhat  below  the  preceding  is  the 
summit  of  the  arytenoid  cartilage  seen  only  during  deep  inspiration.  The  rings  of  the 
trachea,  and  even  the  bifurcation  of  the  trachea  itself,  if  the  patient  be  directed  to  draw 
a  deep  breath,  may  be  occasionally  seen. 

Movements  of  the  Vocal  Cords.  The  position  of  the  vocal  cords  in  ordi- 
nary tranquil  breathing  is  so  adapted  by  the  muscles  that  the  opening  of  the 
glottis  is  wide  and  triangular,  figure  348,  B,  becoming  a  little  wider  at  each 
inspiration,  and  a  little  narrower  at  each  expiration.  On  making  a  rapid 
and  deep  inspiration  the  opening  of  the  glottis  is  widely  dilated,  figure  348,  C, 
and  somewhat  lozenge-shaped. 

In  Vocalization.  At  the  moment  of  the  emission  of  a  note  the  opening  is 
narrowed,  the  margins  of  the  arytenoid  cartilages  being  brought  into  contact 
and  the  edges  of  the  vocal  cords  approximated  and  made  parallel  at  the  same 
time  that  their  tension  is  much  increased.  The  higher  the  note  produced,  the 
tenser  do  the  cords  become,  figure  348,  A;  and  the  range  of  a  voice  depends,  of 
course,  in  the  main,  on  the  extent  to  which  the  degree  of  tension  of  the  vocal 
cords  can  be  thus  altered.  In  the  production  of  a  high  note  the  vocal  cords 
are  brought  well  within  sight,  so  as  to  be  plainly  visible  with  the  help  of  the 
laryngoscope.    In  the  utterance  of  low  tones,  on  the  other  hand,  the  epiglottis 


MOVEMENTS  OF  THE  VOCAL  CORDS 


487 


is  depressed  and  brought  over  the  vocal  cords,  figure  349.  The  epiglottis, 
by  being  somewhat  pressed  down  so  as  to  cover  the  superior  cavity  of  the  lar- 
ynx, serves  to  render  the  notes  deeper  in  tone  and  at  the  same  time  somewhat 
duller,  just  as  covering  the  end  of  a  short  tube  placed  in  front  of  caoutchouc 
tongues  lowers  the  tone.  In  no  other  respect  does  the  epiglottis  appear  to  have 
any  effect  in  modifying  the  vocal  sounds. 

The  degree  of  approximation  of  the  vocal  cords  also  usually  corresponds 
with  the  height  of  the  note  produced;  but  probably  not  always,  for  the  width 


Fir,.  348. — Three  Laryngoscopic  Views  of  the  Superior  Aperture  of  the  Larynx  and  Surrounding 
Parts.  A,  The  glottis  during  the  emission  of  a  high  note  in  singing;  B,  in  easy  and  quiet  inhalation 
of  air;  C,  in  the  state  of  the  widest  possible  dilatation,  as  in  inhaling  a  very  deep  breath.  The 
diagrams  A' ,  B' .  and  C ,  show  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal  ligaments 
and  arytenoid  cartilages  in  the  three  several  states  represented  in  the  other  figures.  In  all  the 
figures,  so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz.:  /,  the  base  of  the  tongue; 
e,  the  upper  free  part  of  the  epiglottis;  e' ,  the  tubercle  or  cushion  of  the  epiglottis;  ph,  part  of  the 
anterior  wall  of  the  pharynx  behind  the  larynx ;  in  the  margin  of  the  aryteno-epiglottidean  fold 
w,  the  swelling  of  the  membrane  caused  by  the  cartilages  of  Wrisberg;  s,  that  of  the  cartilages 
of  Santorini;  a,  the  tip  or  summit  of  the  arytenoi  1  cartilages;  cv,  the  true  vocal  cords  or  lips  of 
the  rima  glottidis;  cvs,  the  superior  or  false  vocal  cords;  between  them  the  ventricle  of  the 
larynx;  in  C,  tr  is  placed  on  the  anterior  wall  of  the  receding  trachea,  and  6  indicates  the  com- 
mencement of  the  two  bronchi  beyond  the  bifurcation  which  may  be  brought  into  view  in  this 
state  of  extreme  dilatation.      (Quain,  after  Czermak.) 


of  the  aperture  has  no  essential  influence  on  the  pitch  of  the  note,  as  long  as  the 
vocal  cords  have  the  same  tension;  only  with  a  wide  aperture  the  tone  is  more 
difficult  to  produce  and  is  less  perfect,  the  rushing  of  the  air  through  the  aper- 
ture being  heard  at  the  same  time. 


488  MUSCLE-NERVE    PHYSIOLOGY 

No  true  vocal  sound  is  produced  at  the  posterior  part  of  the  aperture 
of  the  glottis,  the  part  of  the  aperture  which  is  formed  by  the  space  between 
the  arytenoid  cartilages.  For  if  the  arytenoid  cartilages  be  approximated  in 
such  a  manner  that  their  anterior  processes  touch  each  other,  but  yet  leave  an 
opening  behind  them  as  well  as  in  front,  no  second  vocal  tone  is  produced  by 
the  passage  of  the  air  through  the  posterior  opening,  but  merely  a  rustling 
sound.  The  pitch  of  the  note  produced  is  the  same  whether  the  posterior 
part  of  the  glottis  be  open  or  not. 

The  Voice  in  Singing.  The  laryngeal  votes  may  be  produced  ifi  three 
different  kinds  of  sequence.  The  first  is  the  monotonous,  in  which  the  notes 
have  nearly  all  the  same  pitch  as  in  ordinary  speaking;  the  variety  of  the  sounds 
of  speech  being  due  to  articulation  in  the  mouth.  In  speaking,  occasional 
syllables  receive  a  higher  intonation  for  the  sake  of  accent.  The  second  mode 
of  sequence  is  the  successive  transition  from  high  to  low  notes,  and  vice  versa, 


Fig.  349. — View  of  the  Upper  Part  of  the  Larynx  as  Seen  by  Means  of  the  Laryngoscope 
during  the  utterance  of  a  grave  note,  c.  Epiglottis;  s,  tubercles  of  the  cartilages  of  Santorini;  a, 
arytenoid  cartilages;    z,  base  of  the  tongue;    pit,  the  posterior  wall  of  the  pharynx.      (Czermak.) 

without  intervals;  such  as  is  heard  in  the  crying  in  children  and  in  the  howling 
and  whining  of  dogs.  The  third  mode  of  sequence  of  the  vocal  sounds  is  the 
musical,  in  which  each  sound  has  a  determinate  number  of  vibrations,  and  the 
numbers  of  the  vibrations  in  the  successive  sounds  have  the  same  relative 
proportions  that  characterize  the  notes  of  the  musical  scale. 

The  different  sounds  made  by  the  musical  voice  are  characterized  by  the 
three  properties  of  tones  in  general,  viz.,  the  pitch,  which  is  dependent  on  the 
rate  of  vibration  of  the  vocal  cords;  the  loudness,  which  depends  on  the  force  of 
the  vibration,  and  the  quality  or  timber,  which  is  dependent  on  the  resonance  of 
the  cavities  of  the  respiratory  apparatus,  particularly  of  the  mouth,  pharynx, 
and  nasal  cavities. 

The  Vocal  Range  of  the  Voice.  In  different  individuals  this  com- 
prehends one,  two,  or  three  octaves.  In  singers,  that  is,  in  persons  trained  in 
singing,  it  extends  to  three  or  more  octaves.  But  the  male  and  female  voices 
commence  and  end  at  different  points  of  the  musical  scale.  The  lowest  note 
of  the  female  voice  is  about  an  octave  higher  than  the  lowest  of  the  male  voice; 
the  highest  note  of  the  female  voice  about  an  octave  higher  than  the  highest  of 
the  male.  The  entire  scale  of  the  average  human  voice  includes,  from  the 
lowest  male  note  to  the  highest  female,  about  three  to  three  and  a  half  octaves. 


THE    QUALITY    OF    THE    VOICE  489 

Some  remarkable  musical  voices  have  had  a  range  of  three  and  a  half  octaves. 
A  principal  difference  between  the  male  and  female  voice  is,  therefore,  in  their 
pitch.  But  they  are  also  distinguished  by  the  quality  of  the  tone.  The  voices 
of  men  and  of  women  differ  among  themselves,  both  in  the  general  pitch  and 
in  the  quality.  There  are  two  kinds  of  male  voices,  technically  called  the  bass 
and  tenor,  and  two  of  female  voices,  the  contralto  and  soprano,  all  differing  from 
each  other  in  general  pitch.  The  bass  voice  reaches  lower  than  the  tenor, 
and  its  strength  lies  in  the  low  notes.  The  contralto  voice  is  lower  range  than 
the  soprano,  and  is  strongest  in  the  lower  notes  of  the  female  voice.  The 
barytone  and  mezzo-soprano  voices  are  intermediate  in  range;  the  barytone 
being  intermediate  between  bass  and  tenor,  the  mezzo-soprano  between  the 
contralto  and  soprano.  The  difference  in  the  pitch  of  the  male  and  the  female 
voices  depends  primarily  on  the  different  size  of  the  larynx  and  the  length  of 
the  vocal  cords  in  the  two  sexes;  their  relative  lengths  in  men  and  women  are 
as  three  to  two. 

The  boy's  larynx  resembles  the  female  larynx.  His  vocal  cords  before 
puberty  are  not  two-thirds  the  length  of  the  adult  cords;  and  the  angle  of  the 
thyroid  cartilage  is  as  little  prominent  as  in  the  female  larynx.  Bovs'  voices  are 
alto  and  soprano,  resembling  in  pitch  those  of  women,  but  louder,  and  differing 
somewhat  from  them  in  tone.  But,  after  the  larynx  has  undergone  the  change 
produced  during  the  period  of  development  at  puberty,  the  boy's  voice  becomes 
bass  or  tenor.  While  the  change  of  form  is  taking  place  the  voice  becomes  im- 
perfect, frequently  hoarse  and  crowing,  and  is  unfitted  for  singing  until  the 
readjustment  of  the  larynx  is  complete  and  the  muscles  which  control  the  vocal 
cords  are  again  coordinated.  In  eunuchs  who  have  been  deprived  of  the  testes 
before  puberty,  the  voice  does  not  undergo  this  change.  The  voice  of  most 
old  people  is  deficient  in  tone,  unsteady,  and  more  restricted  in  extent.  The 
first  defect  is  owing  to  the  ossification  of  the  cartilages  of  the  larynx  and  the 
altered  condition  of  the  vocal  cords;  the  want  of  steadiness  arises  from  the 
loss  of  nervous  power  and  command  over  the  muscles,  the  result  of  which  is 
here,  as  in  other  parts,  a  tremulous  movement.  These  two  causes  combined 
render  the  voices  of  old  people  void  of  tone,  unsteady,  and  weak. 

Most  persons  have  the  power,  if  at  all  capable  of  singing,  of  modulating 
their  voices  through  a  double  series  of  notes  of  different  character:  namely,  the 
notes  of  the  natural  yoice,  or  chest-notes,  and  the  falsetto  notes.  The  natural 
voice,  which  alone  has  been  hitherto  considered,  is  fuller,  and  excites  a  dis- 
tinct sensation  of  much  stronger  vibration  and  resonance  than  the  falsetto 
voice,  which  has  mere  of  a  flute-like  character. 

The  Quality  of  the  Voice.  The  difference  in  quality  of  yoices, 
seen  when  two  or  more  persons  sound  the  same  note,  is  due  to  differences  in 
resonance  in  the  cayities  of  the  mouth  and  larynx,  also  of  the  nose.  The 
shape  of  the  roof  of  the  mouth,  the  regularity  of  the  teeth,  and  the  size  of  the 
tongue,  and  the  size  and  clearness  cf  the  nasopharynx  are  all  factors.     The 


490  MUSCLE-NERVE    PHYSIOLOGY 

size  and  shape  of  the  larynx  and  mouth  cavity  which  influence  the  voice 
quality  can  be  controlled  to  some  extent  during  singing,  and  this  is  a  special 
point  of  training  in  voice  culture. 

Speech.  Besides  the  musical  tones  formed  in  the  larynx  a  great 
number  of  other  sounds  can  be  produced  in  the  vocal  tubes,  between  the 
glottis  and  the  external  apertures  of  the  air-passages,  the  combination  of  which 
sounds  into  different  groups  to  designate  objects,  properties,  actions,  etc., 
constitutes  language.  The  languages  do  not  employ  all  the  sounds  which  can 
be  produced  in  this  manner,  the  combination  between  certain  sounds  being 
often  difficult.  Those  sounds  which  are  easy  of  combination  enter,  for  the 
most  part,  into  the  formation  of  the  greater  number  of  languages.  Each 
language  contains  a  certain  number  of  such  sounds,  but  in  no  one  are  all 
brought  together.  On  the  contrary,  different  languages  are  characterized  by 
the  prevalence  in  them  of  certain  classes  of  these  sounds,  while  other  sounds 
are  less  frequent  or  altogether  absent. 

Articulate  Sounds.  The  sounds  produced  in  speech,  or  the  articu- 
late sounds,  are  commonly  divided  into  vowels  and  consonants :  the  distinc- 
tion between  which  is  that  the  sounds  for  the  former  are  generated  by  the 
larynx,  while  those  for  the  latter  are  produced  by  interruption  of  the  current 
of  air  in  some  part  of  the  air-passages  above  the  larynx.  The  term  consonant 
has  been  given  to  these  because  several  of  them  are  not  properly  sounded,  ex- 
cept consonantly  with  a  vowel.  Thus,  if  it  be  attempted  to  pronounce  aloud 
the  consonants  b,  d,  and  g,  or  their  modifications,  p,  t,  k,  the  intonation  fol- 
lows them  only  in  their  combination  with  a  vowel.  To  recognize  the  essential 
properties  of  the  articulate  sounds,  it  is  necessary  first  to  examine  them  as  they 
are  produced  in  whispering,  and  then  investigate  which  of  them  can  also  be 
uttered  in  a  modified  character  conjoined  with  vocal  tone.  By  this  procedure 
we  find  two  series  of  sounds:  in  one  the  sounds  are  mute,  and  cannot  be 
uttered  with  a  vocal  tone;  the  sounds  of  the  other  series  can  be  formed  inde- 
pendently of  voice,  but  are  also  capable  of  being  uttered  in  conjunction  with  it. 

All  the  vowels  can  be  expressed  in  a  whisper  without  vocal  tone,  that  is, 
mutely.  These  mute  vowel  sounds  differ,  however,  in  some  measure,  as  to 
their  mode  of  production,  from  the  consonants.  All  the  mute  consonants  are 
formed  in  the  vocal  tube  above  the  glottis,  or  in  the  cavity  of  the  mouth  or 
nose,  by  the  mere  rushing  of  the  air  between  the  surfaces  differently  modified 
in  disposition.  But  the  sound  of  the  vowels,  even  when  mute,  has  its  source 
in  the  glottis,  though  its  vocal  cords  are  not  thrown  into  the  vibrations  necessary 
for  the  production  of  voice;  and  the  sound  seems  to  be  produced  by  the  passage 
of  the  current  of  air  between  the  relaxed  vocal  cords.  The  same  vowel-sound 
can  be  produced  in  the  larynx  when  the  mouth  is  closed,  the  nostrils  being 
open,  and  the  utterance  of  all  vocal  tone  avoided.  The  sound,  when  the  mouth 
is  open,  is  so  modified  by  varied  forms  of  the  oral  cavity  as  to  assume  the 
characters  of  the  vowels  a,e,  i,  o,  u,  in  all  their  modifications 


ARTICULATE    SOUNDS  491 

The  cavity  of  the  mouth  assumes  the  same  form  for  the  articulation  of  each 
of  the  mute  vowels  as  for  the  corresponding  vowel  when  vocalized;  the  only 
difference  in  the  two  cases  lies  in  the  kind  of  sound  emitted  by  the  larynx. 
It  has  been  pointed  out  that  the  conditions  necessary  for  changing  one  and  the 
same  sound  into  the  different  vowels  are  differences  in  the  size  of  two  parts — 
the  oral  canal  and  the  oral  opening;  and  the  same  is  the  case  with  regard  to  the 
mute  vowels.  By  oral  canal  is  meant  here  the  space  between  the  tongue  and 
palate:  for  the  pronunciation  of  certain  vowels  both  the  opening  of  the  mouth 
and  the  space  just  mentioned  are  widened;  for  the  pronunciation  of  other 
vowels  both  are  contracted;  and  for  others  one  is  wide,  the  other  contracted. 
Admitting  five  degrees  of  size,  both  of  the  opening  of  the  mouth  and  of  the 
space  between  the  tongue  and  palate,  Kempelen  thus  states  the  dimensions  of 
these  parts  for  the  following  vowel  sounds: 

Vowel.  Sound.  Size  of  Oral  Opening.  Size  of  Oral  Canal. 

a      as  in  "  far "  5   3 

a  "        "name"  4   2 

e  "       " theme"  3   1 

0  "       "go"  2   4 

00  "       "  cool "  1   5 

Another  important  distinction  in  articulate  sounds  is  that  the  utterance  of 
some  is  only  of  momentary  duration,  taking  place  during  a  sudden  change  in 
the  conformation  of  the  mouth,  and  being  incapable  of  prolongation  by  a  con- 
tinued expiration.  To  this  class  belong  b,  p,  d,  and  the  hard  g.  In  the 
utterance  of  other  consonants  the  sounds  may  be  continuous;  they  may  be 
prolonged,  ad  libitum,  as  long  as  a  particular  disposition  of  the  mouth  and  a 
constant  expiration  are  maintained.  Among  these  consonants  are  h,  m,  n, 
f,  s,  r,  1.  Corresponding  differences  in  respect  to  the  time  that  may  be  oc- 
cupied in  their  utterance  exist  in  the  vowel  sounds,  and  principally  constitute 
the  differences  between  long  and  short  syllables.  Thus  the  a  as  in  far  and 
fate,  the  o  as  in  go  and  fort,  may  be  indefinitely  prolonged;  but  the  same 
vowels  (or  more  properly  different  vowels  expressed  by  the  same  letters), 
as  in  can  and  fact,  in  dog  and  gotten,  cannot  be  prolonged. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of  combination 
with  vocal  tone  (intonation),  and  are  absolutely  mute;  nearly  all  the  conso- 
nants of  the  second  or  continuous  kind  may  be  attended  with  intonation. 

The  tongue,  which  is  usually  credited  with  the  power  of  speech,  plays 
only  a  subordinate,  although  very  important,  part.  This  is  well  shown  by  cases 
in  which  nearly  the  whole  organ  has  been  removed  on  account  of  disease. 
Patients  who  recover  from  this  operation  talk  imperfectly,  and  their  voices  are 
considerably  modified;  but  the  loss  of  speech  is  confined  to  those  letters  in  the 
pronunciation  of  which  the  tongue  is  particularly  concerned. 

Stammering  depends  on  a  want  of  harmony  between  the  action  of  the 
muscles  (chiefly  abdominal)  which  expel  air  through  the  larynx,  and  that  of 


492  MUSCLE-NERVE    PHYSIOLOGY 

the  muscles  which  guard  the  orifice  (rima  glottidis)  by  which  it  escapes,  and  of 
those  (of  tongue,  palate,  etc.)  which  modulate  the  sound  to  the  form  of  speech. 
Over  either  of  the  groups  of  muscles,  by  itself,  a  stammerer  may  have  as  much 
power  as  other  persons,  but  he  cannot  harmoniously  arrange  their  con- 
joint actions. 


LABORATORY    EXPERIMENTS    ON   MUSCLE  AND   NERVES. 

Physiological  experiments  on  living  muscle  serve  to  demonstrate  many 
of  the  most  fundamental  particulars  of  the  subject.  The  muscles,  especially 
of  cold-blooded  animals,  when  isolated  from  the  body  retain  their  living 
attributes  for  several  hours  under  the  ordinary  conditions  which  can  be  readily 
supplied  in  the  laboratory.  They,  therefore,  serve  as  specially  favorable 
experimental  material. 

The  muscles  of  frogs,  turtles,  and  other  cold-blooded  animals  illustrate 
practically  all  the  facts  which  can  be  shown  by  the  muscles  of  warm-blooded 
animals  and  are  therefore  most  advantageously  used. 

i.  The  Muscle-Nerve  Preparation.  The  classical  muscle-nerve  prep- 
aration is  the  gastrocnemius  muscle  and  the  sciatic  nerve.  Prepare  it 
as  follows:  Kill  the  frog  by  pithing.  This  is  done  by  grasping  the  frog 
firmly  in  one  hand  and  with  the  other  making  a  cut  with  a  blunt  scalpel 
through  the  cranium  just  over  the  medulla,  turning  the  scalpel  so  as  completely 
to  destroy  the  medulla.  Now  take  a  slender  knitting  needle,  quickly  run  it 
up  into  the  cranial  cavity  to  destroy  the  brain,  and  down  the  spinal  canal  to 
destroy  the  cord.  After  a  brief  spasmodic  contraction  of  the  muscles  of 
practically  the  entire  body,  the  frog  remains  limp  and  motionless.  In  making 
the  muscle-nerve  preparation  it  is  better  to  isolate  the  tendon  first,  then  the 
nerve,  and  finally  the  femur.  The  nerve  should  be  prepared  as  long  as  possi- 
ble and  should  not  be  allowed  to  come  in  contact  with  the  skin.  If  the  prep- 
aration is  to  be  used  in  a  moist  chamber,  the  skin  should  be  entirely  re- 
moved; if  it  is  to  be  used  in  the  open  air,  the  skin  should  be  left  on.  Use 
care  not  to  stretch  the  nerve,  and  protect  it  from  evaporation. 

2.  The  Irritability  of  Nerve.     Prepare  a  muscle  nerve  with  its  skin 

on  and  do  not  cut  away  the  foot.     Mount  it  by  inserting  the  femur  in  a 

'  muscle  clamp,  letting  the  leg  extend  vertically  upward,  and  the  foot  hang  over. 

The  nerve  should  lie  along  the  exposed  moist  femur,  one  end  being  slightly 

free.     Stimulate  the  nerve  in  the  following  ways: 

a.  Electrical  Stimuli.  Apply  the  electrodes  from  the  secondary  coil  of  an 
induction  apparatus  to  the  tip  of  the  nerve.  When  an  induction  current  of 
sufficient  strength  is  produced,  the  muscle  to  which  the  nerve  is  attached  will 
give  contractions,  thus  moving  the  foot.  Notice  that  contractions  occur  with 
both  make  and  break  induction.     Apply  the  electrodes  from  the  two  poles  of  a 


IRRITABILITY    OF    MUSCLE  493 

dry  battery.  When  the  current  of  the  battery  is  established  a  contraction  will 
occur,  but  does  not  continue  during  the  time  of  the  flow  of  the  current.  When 
the  current  is  stopped  a  second  contraction  occurs.  The  nerve  is  irritable  to 
both  galvanic  and  faradic  currents. 

b.  Mechanical  Stimuli.  Pinch  the  nerve  lightly  with  forceps,  or  give  it 
a  sudden  stroke  with  the  scalpel  handle.  With  each  mechanical  impact  there 
is  a  single  contraction  of  the  muscle. 

c.  Thermal  Stimuli.  Touch  the  end  of  the  nerve  with  a  glass  rod  heated 
in  boiling  water.  At  each  time  the  nerve  is  brought  in  contact  with  the  rod 
there  will  be  muscular  contraction,  as  in  the  preceding  cases.  The  experi- 
ment succeeds  better  if  the  nerve  comes  in  contact  with  the  rod  for  several 
millimeters  of  length.  If  the  tip  of  the  nerve  has  ceased  to  respond,  then  snip 
it  off  with  the  scissors,  and  repeat  the  experiment  on  the  fresh  end. 

d.  Chemical  Stimulation.  Many  chemical  substances  when  brought  in 
contact  with  living  nerve  fiber  produce  nerve  impulses.  Try  crystals  of  sodium 
chloride,  magnesium  sulphate,  dilute  ammonia,  acetic  acid,  10  per  cent  nitric 
acid,  i  per  cent  mercuric  chloride. 

Tabulate  your  observations  on  all  the  forms  of  stimulation  used  above,  by 
the  following  outline: 


Kind  of  Stimulation. 

Effect  Produced. 

3.  Irritability  of  Muscle.  Repeat  the  experiments  in  number  2 
above,  applying  the  stimuli,  electricity,  etc.,  directly  to  the  muscle  substance, 
choosing  as  far  as  possible  portions  of  muscle  which  do  not  exhibit  nerve 
fiber.  The  muscle  will  usually  respond  by  a  contraction  to  each  of  the  above 
forms  of  stimulation. 

These  tests  do  not  fully  demonstrate  the  direct  irritability  of  muscle  sub- 
stance, since  in  each  case  it  is  possible  that  nerves  may  have  been  stimulated. 
The  nerve  influences  over  the  muscle  can  be  eliminated  by  the  use  of  drugs,  as 
will  be  shown  in  the  next  experiment. 

4.  Independent  Irritability  of  Muscle.  The  influence  of  curara  on 
the  muscle-nerve  preparation  is  demonstrated  as  follows:  Destroy  the  brain 
only  of  a  frog  by  pithing,  taking  care  not  to  injure  the  blood-vessels  of  the 
spinal  canal.  Place  the  animal  on  a  glass  plate  with  its  back  up  and  dissect  out 
the  sciatic  nerve.  Use  care  not  to  injure  in  any  way  the  accompanying  femoral 
artery.  Pass  a  ligature  of  linen  thread  under  the  sciatic  and  around  the  mus- 
cles and  blood-vessels  of  the  leg  so  as  completely  to  shut  off  the  circulation  on 


494 


MUSCLE-NERVE     PHYSIOLOGY 


that  side.  Now  inject  under  the  skin  of  the  back  three  drops  of  i  per  cent 
curara,  allowing  twenty  to  thirty  minutes  for  absorption.  When  the  drug 
is  completely  absorbed,  make  the  following  observations: 

a.  Stimulate  the  muscles  of  the  ligatured  leg,  also  the  muscles  of  the  cura- 
rized  leg,  both  will  contract. 

b.  Stimulate  the  sciatic  nerve  of  the  ligated  leg  below  the  ligature  where 
it  has  not  come  in  contact  with  the  curara;  also  the  sciatic  of  the  opposite 
side,  which  has  come  in  contact  with  the  curara.  Stimulation  of  the  first 
nerve  produces  contraction  of  its  muscle;  of  the  second  nerve  does  not  pro- 
duce contraction  of  its  muscle. 

From  this  experiment  of  Claude  Bernard's  it  is  evident  that  the  curara  does 
not  destroy  the  irritability  of  nerve  fiber  nor  the  irritability  of  the  muscle 
fiber,  yet  it  does  destroy  the  influence  of  the  nerve  over  the  muscle,  probably 
acting  as  a  specific  poison  for  the  motor  end-plates.  If  the  motor  end-plates 
are  destroyed,  then  forms  of  stimuli  which  produce  contractions  of  the  muscle 
must  act  directly  on  muscle  substance,  proving  that  muscle  substance,  as  such, 
is  irritable. 

5.  The  Simple  Muscle  Contraction.  Striated  muscle  responds  to 
electrical  stimuli  even  of  almost  instantaneous  duration.  The  response  which 
the  muscle  gives  to  a  single  stimulus  is  called  a  simple  muscle  contraction, 
and  is  demonstrated  as  follows: 

Make  a  muscle-nerve  preparation  with  the  tendon  isolated  and  the  skin 
removed,  and  mount  it  in  a  moist  chamber,  figure  350.     Connect  the  tendon 


Fig.  3 so. — Moist  Chamber. 


with  a  recording  lever  by  short  copper-wire  hooks.  Lay  the  nerve  across  a 
pair  of  platinum  electrodes,  shake  a  little  water  on  the  sides  of  the  cover  of 
the  moist  chamber,  and  place  it  over  the  preparation  so  as  to  prevent  drying  of 
the  nerve  and  of  the  muscle.     Arrange  an  induction  coil  with  its  keys,  battery, 


THE    SIMPLE    MUSCLE    CONTRACTION 


495 


and  electrodes  connected  as  shown  in  the  diagram,  figure  351.  Set  the  second- 
ary coil  at  a  position  which  will  give  a  strong  contraction  of  the  muscle,  and 
record  this  contraction  on  the  smoked  paper  of  an  ordinary  recording  cylinder. 
Whenever  the  induction  shock  is  sent  through  the  nerve  there  will  be  a  single 
contraction  of  the  muscle.  If  this  contraction  is  recorded  on  the  drum  stand- 
ing still,  then  the  record  will  be  a  vertical  line,  the  height  of  which  can  be 
measured.  From  it  and  the  arms  of  the  lever  the  exact  shortening  of  the  muscle 
can  be  computed.  Repeat  the  stimulus  with  weaker  and  weaker  currents, 
until  no  contraction  is  produced.     As  the  stimulus  becomes  weaker  a  point 


Fig.  351. — Arrangement  of  Apparatus  in  the  Induction  Coil,  as  Shown  for  Single  Inductions. 


is  reached  at  which  the  contractions  rapidly  decrease  in  height  and  cease 
altogether.  If,  on  the  other  hand,  the  stimulus  is  stronger  the  contractions 
only  slightly  increase. 

Arrange  the  apparatus  so  as  to  stimulate  the  muscle  by  an  automatic  key 
attached  to  the  recording  drum.  Adjust  the  apparatus  and  lever  and  revolve 
the  drum  at  a  rapid  rate,  allowing  the  automatic  key  to  be  opened  while  the 
drum  is  turning  at  a  rapid  speed.  Or  take  a  record  on  the  pendulum  myo- 
graph, which  is  especially  constructed  for  this  experiment,  figure  352.  The 
muscle  contraction  now  is  recorded  as  a  wave  which  shows  some  consider- 
able duration  in  time.  Repeat  the  experiment,  introducing  a  100  double 
vibration  tuning  fork  to  record  the  speed  of  the  drum,  and  taking  care  to 
mark  the  exact  point  on  the  record  where  the  automatic  key  is  opened.  In 
this  record  the  muscle  contraction  shows  three  different  periods  or  phases. 
The  first,  a  period  of  no  activity,  called  the  latent  period,  taking  about  0.01 
of  a  second;  the  second,  the  period  of  rapid  shortening  known  as  the  con- 
traction phase,  taking  about  0.04  of  a  second  on  the  average;  and  the  third, 
a  period  of  rapid  relaxation  or  return  to  the  normal,  which  takes  about  0.05 
of  a  second,  see  figure  353. 

The  time  and  character  of  the  simple  muscle  contraction  will  be  influenced 
by:   i,  load  or  tension;  2,  the  exact  temperature;  3,  by  the  amount  of  work 


49C 


MUSCLE-NERVE    PHYSIOLOGY 


it  has  previously  done,  or  fatigue ;  4,  by  the  time  since  it  was  isolated  from  the 
circulation.  Perform  a  series  of  experiments  varying  these  effects,  and  record 
the  results  by  the  following  outline: 


Number  of 

the 
Experiment. 

Muscle 
Used. 

Temper- 
ature. 

Load. 

Total  Time  of 

Contraction, 

in  Seconds. 

Latent 
Period,  in 
Seconds. 

Contraction 

Period,  in 

Seconds. 

Relaxation 
Period,  in 
Seconds. 

6.  The  Relation  of  the  Contraction  to  the  Strength  of  the  Stimu- 
lus. Minimal  and  Maximal  Stimuli.  Prepare  a  muscle-nerve  of  the 
frog  and  mount  in  the  moist  chamber  and  arrange  for  stimulating  the  muscle 
directly  by  means  of  the  secondary  current  of  the  induction  coil,  with  the  ap- 


>*%S; 


Fig.  352.— Simple  Form  of  Pendulum  Myograph  and  Accessory  Parts.  A,  Pivot  upon  which 
pendulum  swings;  B,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its  swing;  D,  a  spring- 
catch  which  retains  myograph,  as  indicated  by  dotted  lines,  and  on  pressing  down  the  handle  of 
which  the  pendulum  swings  along  the  arc  to  D  on  the  left  of  figure,  and  is  caught  by  its  spring. 

paratus  adjusted  as  in  figure  351.  Prepare  a  recording  cylinder  for  making 
vertical  records  of  the  contractions.  Adjust  the  writing  point  of  the  muscle 
lever  to  the  drum  and  move  the  drum  by  hand  1  cm.  after  each  succeeding 
contraction.  Set  the  secondary  coil  of  the  induction  apparatus  so  that  it  will 
be  too  weak  to  produce  a  stimulus.     Now  attempt  to  stimulate  the  muscle, 


THE     EFFECT    OF    FATIGUE  497 

then  move  the  induction  coil  toward  the  primary  i  cm.  at  a  time  and  repeat 
until  the  first  slight  contraction  appears.  Continue  to  slide  the  secondary  coil 
toward  the  primary,  stimulate  at  each  new  position,  moving  the  drum  forward 


FlO.  353- — Record  of  a  Simple  Contraction  of  the  Gastrocnemius  of  the  Frog.  Time  in  .01 
of  a  second.  St,  Moment  of  stimulation.  Record  taken  on  a  rapid  drum  that  was  provided  with 
an  automatic  key. 

for  each  stimulus  as  directed,  until  a  series  of  contractions  is  obtained 
through  the  range  of  variation  of  induction  of  which  the  apparatus  is  capa- 
ble, usually  twenty  to  thirty  contractions. 

A  typical  tracing,  figure  326,  shows  that  as  the  strength  of  the  stimulus  is 
increased  the  amplitude  of  the  contractions  quickly  mounts  from  the  minimal 
to  a  maximal,  after  which  all  further  increase  in  the  strength  of  the  stimulus 
produces  contractions  of  practically  the  same  height.  The  first  perceptible 
contraction  is  called  the  minimal  contraction,  the  strength  of  the  current  which 
produced  it  a  minimal  stimulus  for  that  preparation.  The  contractions  of 
the  greatest  amount  are  called  maximal  contractions.  The  weakest  stimulus 
which  produces  a  maximal  contraction  is  called  the  maximal  stimulus,  and 
all  stronger  stimuli  supramaximal. 

7.  The  Effect  of  Fatigue  on  the  Amplitude  of  the  Simple  Muscle 
Contraction.  Prepare  a  gastrocnemius  muscle  for  direct  stimulation 
and  mount  it  in  a  moist  chamber.  Arrange  the  induction  apparatus  for  single 
stimuli.  Adjust  the  recording  lever  of  the  muscle  to  a  smoked-paper  kymo- 
graph and  set  the  speed  of  the  kymograph  to  revolve  at  the  rate  of  1  mm.  per 
second.  Now  stimulate  the  muscle  with  the  make  induction  (short-circuiting 
the  break)  once  every  two  seconds.  The  contractions  will  be  recorded  as  vertical 
marks  on  the  drum  in  regular  order,  at  a  distance  of  2  mm.  apart,  hence  very 
slight  changes  in  amplitude  are  readily  detected.  The  contractions  gradually 
increase  in  height  for  the  first  ten  or  twenty,  the  phenomenon  of  treppe,  then 
run  for  from  fifty  to  one  hundred  contractions  of  practically  uniform  ampli- 
tude, after  which  there  is  a  gradual  but  sharp  decrease  known  as  fatigue. 
Repeat  the  experiment  after  ten  minutes'  rest.  The  former  variations  occur 
now  very  rapidly,  indicating  that  the  fatigue  effects  are  only  partially  recov- 
ered from. 
32 


498  MUSCLE-NERVE     PHYSIOLOGY 

8.  The  Effect  of  Fatigue  on  the  Time  of  the  Simple  Contraction. 
Prepare  a  muscle-nerve  and  mount  it  in  the  moist  chamber,  arrange  for  the 
record  as  directed  under  5  above.  Make  a  series  of  records  of  the  simple 
contraction  when  automatically  stimulated,  recording  only  every  tenth  or 
twentieth  contraction — the  intermediate  contractions  should  be  shunted  and 
are  used  merely  to  produce  fatigue.  After  a  time  the  contractions  will  not 
only  diminish  in  amplitude,  but  there  will  be  a  gradual  increase  in  the  time 
consumed  by  the  contraction.     This  increase  in  time  falls  very  slightly  on 


Fig.  354. — Contractions  of  the  Gastrocnemius  Muscle  to  Show  Fatigue.    The  numbers  printed 
on  the  figure  indicate  the  contraction  in  the  series  which  is  recorded.      (Lee.) 

the  latent  period,  is  more  pronounced  in  the  contraction  phase,  but  is  very 
marked  in  the  relaxation  phase,  figure  354. 

9.  Fatigue  of  Voluntary  Muscular  Contraction.  The  human  vol- 
untary muscles  are  used  to  demonstrate  this  experiment.  Use  a  Mosso's 
ergograph,  or  any  one  of  its  numerous  modifications.  If  the  original  form  is 
used,  then  the  muscle  should  be  loaded  with  about  3  kilos,  and  contractions 
once  a  second  recorded  until  the  muscle  can  no  longer  lift  the  load.  The  load 
may  have  to  be  adjusted  to  the  individual,  but  should  be  chosen  so  that  ex- 
haustion will  be  obtained  with  about  fifty  contractions.  This  experiment  does 
not  demonstrate  complete  exhaustion,  but  merely  fatigue  down  to  a  certain 
level.  If  an  apparatus  is  previously  arranged  for  direct  stimulation  of  the 
muscles  by  electric  currents  it  will  be  found  that  the  contractions  of  the  muscles 
still  occur  after  the  voluntary  power  is  lost,  showing  that  at  least  a  part  of 
the  phenomenon,  possibly  the  chief  part,  is  located  in  the  nervous  tissue  rather 
than  in  the  muscle  substance. 

10.  The  Effect  of  Temperature  on  Muscle  Contractions.  Pre- 
pare a  muscle-nerve  and  mount  it  in  Porter's  latest  form  of  temperature  ap- 
paratus. Adjust  the  levers  for  vertical  records  on  the  smoked  paper  of  the 
kymograph.  Begin  with  a  temperature  of  the  tap  water  and  gradually  lower 
the  temperature  of  the  preparation  by  adding  small  amounts  of  crushed  ice 
at  first,  later  ice  and  some  salt  crystals,  to  the  external  chamber.     Take  care 


THE    EFFECT    OF   TEMPERATURE  499 

to  lower  the  external  temperature  very  slowly  and  gradually, — say  about  one 
degree  in  two  minutes.  Stimulate  the  muscle  with  a  supramaximal  stimulus 
twice  in  rapid  succession,  for  i°  C.  of  change.  Record  these  contractions  as 
pairs  of  vertical  marks  on  the  drum  i  mm.  apart,  separating  each  pair  by  a 
space  of  i  cm.  When  o°  C.  is  reached,  or  before  if  the  muscle  fails  to  contract 
at  a  higher  temperature,  reverse  the  direction  of  the  temperature  change, 
gradually  but  slowly  increase  it  until  the  muscle  goes  into  heat  rigor,  which 
begins  at  from  380  to  400  C. 

While  the  muscle  is  entering  rigor,  move  the  drum  1  cm.  for  each  degree, 
as  before,  so  as  to  record  the  development  of  that  process. 

n.  The  Effect  of  Temperature  on  the  Time  of  the  Simple  Con- 
traction. Repeat  the  preceding  experiment,  but  record  the  con- 
tractions by  the  method  described  in  experiment  5  above,  recording  a  con- 
traction for  every  change  of  50  C.  Measure  the  time  and  amplitude  of  the 
different  contractions,  and  the  phases  of  the  simple  contractions,  and  tabulate 
them  as  shown  in  experiment  5. 

12.  Effect  of  Load  on  the  Height  of  the  Contraction  and  on  the 
Work  of  Voluntary  Muscle.  Make  a  muscle-nerve  preparation  and 
arrange  it  for  stimulation,  as  in  experiment  6  above.  Set  the  induction  coil 
of  the  stimulating  apparatus  for  an  effective  supramaximal  stimulus.  Re- 
cord the  contractions  as  a  series  of  vertical  lines  on  the  kymograph,  separated 
by  a  distance  of  1  cm.  Begin  with  the  load  of  the  lever  only  for  the  first 
contraction,  then  increase  the  load  by  steps  of  20  grams  each  until  the  muscle 
is  no  longer  able  to  lift  the  weight  used.  Support  the  lever  under  a  tension 
of  20  grams.  Use  care  that  no  mechanical  changes  of  the  apparatus  are  re- 
corded on  the  smoked  cylinder.  Repeat  the  experiment  on  a  fresh  muscle, 
but  do  not  support  the  lever. 

The  amount  of  work  done  by  the  muscle  at  each  contraction  is  the  prod- 
uct of  the  load  in  grams  times  the  height  in  centimeters.  The  height  of 
the  lift  can  be  obtained  in  this  experiment  from  the  height  of  the  record  on 
the  drum  and  the  length  of  the  recording  arm  and  power  arm  of  the  lever,  in 
which  the  length  of  the  recording  lever  is  to  the  length  of  the  power  lever 
as  the  height  of  the  record  obtained  is  to  the  actual  shortening  of  the  muscle. 
Compute  the  exact  amount  of  work  done  by  each  contraction  under  varying 
loads,  and  tabulate  on  co-ordinate  paper.  Compare  the  variation  in  work 
done  with  the  variation  in  amplitude  of  the  contraction. 

13.  Tetanus.  A  continued  contraction  of  a  voluntary  muscle  can 
be  shown  to  be  a  fusion  of  simple  muscle  contractions.  This  is  called  a  tetanus. 
Prepare  a  muscle -nerve  in  the  moist  chamber  and  arrange  the  induction  coil 
for  stimulating  with  a  series  of  rapidly  repeated  stimuli.  The  rate  of  the 
stimulation  is  obtained  from  the  tetanometer,  a  form  of  key  for  rapidly  in- 
terrupting the  current,  which  should  be  connected  with  the  primary  coil  in- 
stead of  the  key,  K,  figure  351.     Stimulate  the  muscle  at  a  rate  of  10  per 


500 


MUSCLE-NERVE     PHYSIOLOGY 


second,  record  the  contractions  on  the  drum  moving  at  a  speed  of  about 
2  cm.  per  second.  Use  care  not  to  overfatigue  the  muscle,  i.e.,  stimulate 
it  only  2  or  3  seconds  at  a  time.  Repeat  this  test,  increasing  the  rate  of  stimu- 
lation each  time  by  5,  that  is,  stimulate  at  10,  15,  20,  etc.,  per  second.  In  the 
first  stimulus  there  will  be  a  series  of  simple  contractions  with  almost  com- 
plete intervening  relaxations.  As  the  rate  is  increased  these  relaxations  be- 
come less  and  less  until  presently  a  rate  is  found  which  produces  continuous, 
apparently  uninterrupted  contraction.  This  is  a  tetanus,  the  others  are  incom- 
plete tetani.  The  frog's  gastrocnemius  at  a  temperature  of  200  C.  is  tetanized 
with  a  stimulation  of  from  25  to  35  per  second. 

14.  Cardiac  Muscle.      Cardiac  muscle    differs    from    voluntary  in 
that  the  contractions  occur  rhythmically  and  automatically.     This  is  shown 


Fig.  354  A. — Arrangement  of  Apparatus  for  Studying  the  Contractions  of  the  Strip  of  the  Apex 

of  the  Ventricle. 


by  the  isolated  frog's  heart,  which  continues  to  contract  when  bathed  with 
blood  or  salt  solution,  often  for  hours.  This  isolated  heart,  however,  has  a 
complicated  local  nervous  mechanism.  The  apex  of  the  ventricle  of  the 
terrapin's  heart  is  practically  free  from  nerve  ganglia  and  may  be  used  to 
demonstrate  the  characteristics  of  pure  cardiac  muscle.  Cut  a  strip  off  the 
apex  of  the  terrapin's  ventricle,  as  shown  in  figure  214,  and  mount  it  by  means 
of  light  silk-thread  ligatures  tied  around  the  two  ends  of  a  strip  and  attached 
to  the  apparatus  shown  in  figure  215.  When  such  ventricular  strips  are 
immersed  in  ordinary  0.7  per  cent  sodium  chloride  they  will  begin  contractions 
in  a  few  minutes,  twenty  minutes  or  so.  The  contractions  will  be  regular  in 
rate  and  will  continue  through  two  or  three  hours,  gradually  becoming 
smaller  and  smaller  until  the  standstill  is  reached.  If  the  strip  is  im- 
mersed in  its  own  serum  it  will  give  only  occasional  contractions,  but  it  re- 


INVOLUNTARY     MUSCLE  501 

mains  irritable  and  capable  of  contracting  at  any  moment.  If  changed  to 
salt  solution,  the  salt  solution  apparently  brings  out  the  automatic  rhythm 
by  an  increase  in  its  irritability.  Portions  of  the  auricle  and  of  the  sinus, 
especially  the  latter,  are  more  highly  rhythmic  than  portions  of  the  ventricle, 
due  to  a  specific  difference  in  the  muscle  cells  themselves  and  not  to  the  nervous 
mechanism. 

Refer  to  the  experiments  on  cardiac  muscle  at  the  end  of  the  chapter  on 
Circulation. 

15.  Involuntary  Muscle.  Strips  of  smooth  or  involuntary  mus- 
cle, cut  from  the  stomach  of  a  frog  or  terrapin  or  from  the  intestine  of  a  frog, 
may  be  used  to  show  the  physiology  of  this  character  of  tissue.  Mount  a 
strip  in  the  moist  chamber,  or  in  the  apparatus  shown  in  figure  354  A,  using 


Fig.  355. — Figure  Showing  the  Type  of  Contraction  of  a  Strip  of  Muscle  from  the  Stomach  of  a 
Frog.  The  muscle  was  stimulated  with  an  interrupted  current  during  the  time  indicated  by  the 
signal  tracing,  immediately  below  the  time  tracing.     Time  in  seconds. 

care  not  to  load  it  too  heavily;  the  weight  of  the  ordinary  muscle  lever  may 
produce  too  much  tension.  Stimulate  the  muscle  for  one  or  two  seconds  with 
interrupted  induction  currents  of  moderate  strength.  Contractions  will  follow, 
usually  developing  very,  very  slowly  as  compared  with  striated  muscle,  and 
lasting  through  many  seconds,  from  thirty  to  one  hundred  seconds.  By  using 
very  strong  inductions  occasionally  a  contraction  may  be  secured  with  a 
single  stimulus,  but  single-induction  currents  as  a  rule  do  not  produce 
effective  stimuli  for  smooth  muscle,  which  requires  a  more  slowly  developed 
stimulus. 

If  the  stomach  muscle  of  the  frog  be  used  and  it  be  handled  with  extreme 
care,  it  may  happen  that  automatic  contractions  will  develop  in  the  muscle 
in  the  moist  chamber.  If  so,  these  contractions  will  be  found  to  be  slow  and 
of  varving  amplitude.  The  terrapin's  stomach  muscle  will  ordinarily  not 
show  automatic  contractions,  but  by  increasing  the  temperature  to  about 


502  MUSCLE-NERVE     PHYSIOLOGY 

300  C.  automatic  contractions  will  sometimes  occur  in  it.  Smooth  muscle 
responds  like  voluntary  muscle  to  variations  in  temperature,  to  fatigue,  strength 
of  stimulus,  etc.,  etc. 

16.  Ciliary  Contractions.  Ciliated  Epithelium.  Make  a  prepara- 
tion of  ciliated  epithelium  by  cutting  out  the  esophagus  of  a  terrapin  or  frog, 
slitting  it  open  longitudinally,  and  smoothing  it  out  on  a  cork  block.  The  cilia 
of  this  membrane  will  drive  in  the  direction  down  the  esophagus.  Test  the 
rate  at  which  different  loads  are  moved  and  measure  the  distance  on  the  prep- 
aration as  follows:  Cut  pieces  of  clean  white  paper  about  4  and  6  mm.  square. 
Select  a  favorable  area  on  the  ciliated  surface  as  long  as  possible,  place  the  4 
mm.  square  paper  at  the  beginning  of  the  area,  and  measure  the  time  which  it 
takes  to  travel  the  distance.  Measure  the  speed  in  terms  of  seconds  per  cen- 
timeter. Now  replace  the  paper  at  the  point  of  beginning  and  load  it  with 
small  weighed  cubes  of  paraffin.  The  rate  at  which  the  load  is  carried  will 
slightly  increase  at  first  as  the  load  is  increased,  but  later  will  sharply  decrease. 
Elevate  one  end  of  the  ciliated  membrane  and  repeat  the  experiment  with 
different  loads  so  that  the  cilia  will  now  carry  the  load  uphill.  Calculate  the 
work  done  in  terms  of  gramcentimeters  of  work  per  square  centimeter  of 
ciliated  surface  acting  on  the  load. 


CHAPTER    XIV 
THE  NERVOUS  SYSTEM 

The  nervous  system  consists  of  an  extremely  complex  anatomical  mass 
of  nerve  cells  and  fibers.  It  is  usually  described  as  made  up  of  two  main 
divisions,  the  cerebro-spinal  system  and  the  sympathetic.  These  two  divisions 
must  be  regarded  as  parts  of  one  great  whole,  and  in  no  sense  coordinate. 
The  gross  subdivision  of  the  nervous  system  may  be  given  as  the  following: 
— first,  the  cerebro-spinal  axis,  which  consists  of  matter  within  the  bony 
cranium  and  spinal  column,  constituting  the  brain  and  cord.  Second,  smaller 
masses  for  the  most  part  in  the  abdominal  and  thoracic  cavities,  also  in  the 
neck  and  head,  and  constituting  the  sympathetic  ganglia.  Third,  the  nerves 
or  bundles  of  nerve  fibers  which  connect  the  central  nerve  axis  with  the  per- 
iphery and  with  the  sympathetic  ganglia.  Fourth,  there  are  special  peripheral 
organs  in  connection  with  the  beginnings  and  endings  of  the  nerve  fibers,  the 
one  for  receiving  nerve  stimuli,  the  other  for  transmitting  stimuli  to  other  tis- 
sues. These  are  properly  parts  of  the  nervous  system.  The  peripheral 
organs  for  receiving  stimuli  constitute  the  sense  organs  and  will  be  treated  in 
a  separate  chapter. 

I.  FUNCTION  OF  THE  NERVE  CELL. 

The  Nerve  Cell.  The  nerve  cell,  the  neurone,  may  be  considered 
the  anatomical  and  physiological  unit  of  the  nervous  system.  The  details 
of  the  structure  of  the  nerve  cell,  both  its  body  and  its  processes,  have 
already  been  given  in  chapter  II.  It  is  sufficient  to  recall  that  the  types  of 
nerve  cells  found  in  various  parts  of  the  nervous  system  vary  extremely. 
The  peculiar  feature,  however,  consists  in  the  fact  that  the  cell  body  has 
one  or  more  processes.  Sometimes  these  processes  are  short  but  com- 
plexly branched,  sometimes  they  are  exceedingly  long  as  compared  with  the 
extent  of  the  cell  body.  The  cell  processes  may  or  may  not  be  medullated 
and  subdivided  into  nodes,  but  the  axis-cylinder  process  is  to  be  regarded  as 
a  continuity  of  the  protoplasm  of  the  cell  body.  In  recent  years  the  struct- 
ure of  the  cell  body  and  its  branches  has  been  very  carefully  investigated, 
with  the  result  that  we  are  finding  that  the  intimate  structure  is  very  complex. 
Networks  of  neurofibrillar  have  been  described  not  only  in  the  cell  body,  but 
extending  throughout  the  course  of  the  processes  and,  in  fact,  from  cell  to  cell. 
We  are  not  in  a  position  at  the  present  time  fully  to  determine  what  bearing 

503 


504  THE     NERVOUS     SYSTEM 

these  neurofibrillae  have  on  our  accepted  theories  of  nerve  function,  other  than 
that  they  are  assumed  to  be  the  conducting  elements. 

The  Neurone  Theory.  Our  knowledge  of  the  function  of  the  nerv- 
ous system  is  best  explained  on  the  basis  of  the  neurone  theory,  which 
considers  the  nerve  cell  as  a  physiological  unit.  By  this  view  each  gross 
division  of  the  nervous  system  is  supposed  to  consist  of  a  large  number  of 
individual  neurones,  each  of  which  is  a  more  or  less  complete  morphological 
unit  capable  of  carrying  on  certain  functions  of  its  own.  Each  of  these 
neurones  maintains  physiological  continuity  with  its  associates,  presumably 
by  protoplasmic  contact  rather  than  by  continuity;  so  that  well-marked  paths 
of  conduction  are  possible  throughout  the  extent  of  the  particular  mass  of 


WV.      -ViXo 


/         „is  *        _   \:\ 


■  ■:■■     ■■■K;^v;iV^^  •      ■'■■■ '(? 


\/ 


B  mmwmmm 

Fig.  356. — Purkinje  Cells  from  the  Cerebellum  of  the  Swallow.     A,  Taken  in  the  morning;    B, 
taken  in  the  evening.      (Hodge.) 

which  the  neurone  is  a  part,  and  throughout  the  adjacent  masses.  By  this 
view,  paths  of  conduction  are  made  up  of  series  of  individual  neurones  which 
are  in  physiological  continuity. 

The  Characteristics  of  the  Individual  Nerve  Cell.  The  function 
of  the  nerve  cell  may  be  discussed  under  two  headings:  The  function  of  the 
cell  body,  and  the  function  of  the  cell  processes. 

The  cell  body  of  the  nerve  cell  is  the  part  that  contains  the  nucleus  and  is 
the  center  of  those  activities  which  influence  the  metabolism  of  the  cell  itself. 
If  the  cell  body  be  isolated  from  its  processes,  the  processes  will  degenerate, 
while  the  body  continues  to  live.  In  other  words,  the  cell  body  may  be  con- 
sidered as  the  center  of  those  trophic  influences  which  regulate  the  nutrition 
of  the  processes.     Although  the  nerve  cell  as  a  whole  is  in  many,  perhaps  in 


THE    CHARACTERISTICS    OF   THE    INDIVIDUAL   NERVE    CELL 


505 


most,  cases  a  conducting  organ,  still  those  physiological  processes  which  go  on 
in  it  produce  marked  changes  in  the  protoplasm  of  the  cell  body.  Hodge  has 
demonstrated  that  nerve  cells  which  have  been  active  for  several  hours,  in 
case  of  sparrows  which  have  been  flying  about  actively  throughout  the  day,  or  in 
bees  after  a  day's  work,  show  marked  evidences  of  fatigue.     These  evidences 


Fig.  356  A.— Spinal  Ganglion  Cells  from  the  Cat.     A,  Normal  taken  before  stimulation;  B,  taken 
alter  five  hours'  stimulation.      From  the  right  and  left,  eight  thoracic  ganglia.      (Hodge..) 


consist  in  the  decrease  in  the  size  of  the  nucleus  and  the  appearance  of 
vacuoles  in  its  structure,  also  in  the  shrinking  of  the  protoplasm  of  the  cell, 
which,  in  case  of  the  cells  of  the  spinal  ganglia,  iraws  away  from  its  capsule. 
If  the  cells  are  examined  early  in  the  morning,  then  these  fatigue  changes  will 
not  be  present,  the  cell  having  recuperated  during  the  rest  of  the  night.     It 


506  THE    NERVOUS    SYSTEM 

has  also  been  found  that  the  Nissl  granules  which  are  present  in  the  cell  body 
of  resting  cells  decrease  in  number  and  show  evidence  of  disintegration  in 
cells  that  have  been  stimulated  for  several  hours. 

The  nerve  processes  or  fibers  are  primarily  conducting  structures.  But 
their  fibers  are  susceptible  to  artificial  stimulation,  as  shown  in  the  previous 
chapter,  that  is,  they  are  irritable.  They  are  influenced  by  certain  changes  in 
the  environment,  but  they  do  not  show  evidence  of  fatigue  upon  prolonged 
functional  activity. 

Nutritive  Influence  of  the  Cell  Body  over  its  Processes — Wallerian 
Degeneration.  The  control  of  the  cell  body  over  the  nutrition  of  the 
cell  processes  is  demonstrated  by  the  changes  which  occur  when  these  proc- 
esses are  severed  from  connection  with  the  cell  body.  Under  such  conditions 
the  axis-cylinder  process  completely  degenerates.  Howell  and  Huber  have 
followed  the  degenerative  changes  in  medullated  nerve  fibers.  The  medullated 
fiber  in  the  course  of  three  or  four  days,  in  mammals,  breaks  up  into  elliptical 
segments  of  myelin,  containing  small  fragments  of  the  axis-cylinder.  These 
changes  in  the  cut-off  section  of  nerve  occur  simultaneously  throughout  its 
whole  extent.  In  the  course  of  a  few  weeks  regenerative  changes  begin,  ap- 
parently under  trophic  influence  of  the  nuclei  of  the  primitive  sheath.  These 
nuclei  increase  in  number  and  form  small  masses  of  protoplasm  which  ulti- 
mately produce  a  strand  of  embryonic  protoplasm,  which  is  described  as  the 
"  band  fiber."  If  the  ends  of  the  sectioned  nerve  have  originally  been  brought 
together  and  sutured  in  place,  then  the  axis-cylinder  processes  of  the  portion  of 
the  nerve  fiber  still  attached  to  the  cell  body  will  grow  down  into  the  peripheral 
fibers,  thus  forming  new  axis-cylinder  processes  along  the  course  of  the  band 
fiber.  If  the  stumps  of  the  nerves  are  not  so  brought  together,  then  apparently 
the  band  fiber  again  degenerates,  especially  in  adult  tissues,  though  it  has  been 
claimed  by  Bethe  and  others  that  complete  regeneration  of  the  peripheral 
fiber  will  take  place  in  very  young  animals.  Even  if  complete  regeneration 
takes  place  in  the  peripheral  fiber,  unless  connection  is  established  between  it 
and  the  central  end  of  the  fiber  it  will  ultimately  disintegrate  and  can  only 
temporarily  carry  on  any  physiological  function. 

The  central  end  of  the  divided  nerve,  that  is,  the  part  maintaining  con- 
nection with  the  cell  body,  usually  degenerates  for  a  few  nodes  only,  then  re- 
generation and  growth  of  the  original  stump  proceed.  Instances  are  observed 
in  certain  cases  where  the  degeneration  of  the  entire  central  fiber,  including  its 
cell  body,  takes  place.  This  happens  particularly  in  those  relations  where  the 
original  neurone  forms  a  link  in  a  conducting  path. 

In  conclusion,  one  may  infer  that  the  cell  body  exercises  a  nutritive  or 
trophic  control  over  the  protoplasm  of  its  branches,  just  as  we  have 
already  seen  the  neurone  as  a  whole  exercises  trophic  control  over 
the  nutritive  processes  taking  place  in  the  tissue  to  which  its  branches  are 
distributed. 


TRANSMISSION    OF    IMPULSES   THROUGH    THE    NERVE    CELL  507 

Specific  Energy  of  the  Nerve  Impulses.  We  have  already  discussed 
the  fact  that  a  nerve  fiber,  also  its  cell  body,  is  irritable  to  various  forms  of 
mechanical,  electrical,  etc.,  stimuli.  In  the  complex  differentiation  of  the 
nervous  system  it  is  found  that  whatever  the  form  of  the  external  stimulus 
applied  to  a  nerve  the  resulting  nerve  impulse  produces  the  same  effects  in  the 
central  nervous  system.  This  idea  has  been  called  the  specific  energy  oj  the 
nerve  impulse,  and  was  first  advanced  by  Johannes  Muller. 

Transmission  of  Nerve  Impulses  through  the  Nerve  Cell.  The  the- 
ory has  been  advanced  that  in  the  nerve  cell  the  primary  function  of  some 
processes  is  to  carry  nerve  impulses  toward  the  cell  body,  and  of  other  processes 
to  carry  nerve  impulses  away  from  the  cell  body.  At  the  present  time  this 
view  is  advocated  by  perhaps  the  ablest  living  anatomists  and  neurologists. 
The  dendrites  conduct  toward  the  cell  body,  and  the  axones  away  from  it. 
That  is,  the  former  are  cellulipetal,  the  latter  cellulifugal. 

Impressions  made  upon  the  terminations  or  upon  the  trunk  of  a  cellulifugal 
nerve  may  cause,  a,  pain  or  some  other  kind  of  general  sensation;  b,  special 
sensation;  c,  reflex  action  of  some  kind;  or  d,  inhibition  or  restraint  of  action. 
Similarly  impressions  made  upon  a  cellulipetal  nerve  may  cause,  a,  contraction 
of  muscle  (motor  nerve);  b,  it  may  influence  nutrition  (trophic  nerve); 
c,  it  may  influence  secretion  (secretory  nerve) ;  or  d,  inhibit,  augment,  or  stop 
any  other  efferent  action. 

By  artificial  stimulation  nerve  impulses  can  be  made  to  pass  in  both  di- 
rections in  all  classes  of  nerve  processes.  That  is  to  say,  if  a  motor  axone  is 
stimulated  in  the  middle  of  its  course  it  will  not  only  convey  a  nerve  impulse 
to  its  distribution,  but  also  a  nerve  impulse  will  pass  back  over  the  fiber  to 
the  cell  body  and  out  over  the  dendrites.  Normally,  in  the  complex  of  the 
body  it  is  probable  that  such  a  neurone  will  be  stimulated  only  at  its  points 
of  contact  with  other  neurones  chiefly  through  its  dendrites,  and  especially 
by  means  of  the  sensory  cells.  The  dendrites  will  therefore  receive  the  nerve 
stimulus,  carry-  it  through  the  cell  body  to  the  axone  and  its  distribution- 
In  such  cells  there  is  isolated,  or  uninterrupted,  conduction  throughout  the 
extent  of  the  neurone.  The  nerve  impulse  is  able  to  pass  from  a  given 
neurone  to  adjacent  ones  only  at  the  termination  of  the  axone  or  its  branches, 
which  may  be  considered  as  special  organs  for  the  transference  of  the  nerve 
impulses.  This  activity  involves  isolated  conduction  in  nerve  fibers  bound  in 
a  common  nerve  trunk.  It  has  been  supposed  that  the  myelin  sheath  of  a 
medullated  nerve  acts  as  an  insulator  of  the  axis-cylinder,  but  this  can  be 
only  relatively  true,  for  the  reason  that  non-medullated  nerves  do  not  possess 
the  myelin  sheath.  In  non-medullated  nerves  we  must  suppose  that  the 
primitive  sheath  is  sufficient  to  give  insulated  conduction,  or  that  it  is  an  in- 
herent property  of  the  axis-cylinder  itself  to  carry  the  nerve  impulse  without 
transmission  to  adjacent  fibers. 

We  have  already,  page  470,  discussed  the  rate  of  transmission  of  the  nerve 


508  THE     NERVOUS     SYSTEM 

impulse  in  motor  nerves.  In  sensory  nerves  the  rate  is  said  to  be  somewhat 
higher;  in  human  nerve  from  30  to  42  meters  per  second. 

Physiological  Types  of  Nerve  Cells.  Many  classifications  could 
be  made  of  nerve  cells,  based  on  the  differences  in  their  functional  relations, 
but  at  this  place  attention  will  be  called  to  only  one.  Nerve  cells  may  be 
classified  as  afferent  or  sensory,  efferent  or  motor,  and  connecting  or  trans- 
mitting cells. 

Under  afferent  neurones  are  classed  all  those  neurones  which  transmit 
the  effects  of  external  stimuli  received  through  the  sense  organs,  both  general 
and  special  sense  organs.  These  neurones  carry  nerve  impulses  toward  the 
central  nervous  system,  ultimately  producing  those  changes  in  the  cerebral 
cortex  which  are  associated  with  states  of  consciousness. 

Under  efferent  neurones  are  included  all  those  which  transmit  nerve  im- 
pulses from  any  part  of  the  central  nervous  system  to  the  muscles,  that  is, 
motor  nerves;  or  transmit  nerve  impulses  to  the  glands,  secretory  nerves;  or 
that  transmit  nerve  impulse,  which  inhibit  peripheral  action,  inhibitory  nerves. 

Under  central  or  transmitting  neurones  may  be  included  those  units  which 
act  as  connecting  links  within  the  central  organ,  especially  within  coordinate 
parts  of  the  central  nervous  system,  between  the  afferent  and  efferent  neurones. 

Nerve  Centers.  Whenever  a  number  of  neurones  are  gathered 
in  one  group  to  accomplish  some  specific  function  it  is  called  a  nerve 
center.  The  term  usually  applies  to  the  aggregation  of  cell  bodies  and  their 
dendritic  processes  in  contradistinction  to  nerve  trunks.  There  are  aggre- 
gations of  nerve  cells  into  different  specific  groups,  to  which  we  cannot  in  every 
case  ascribe  a  specific  function.  These  groups  are  not  called  nerve  centers, 
but  are  described  by  the  general  anatomical  term,  ganglia.  Such  ganglia 
are  represented  by  the  sympathetic  chain,  the  spinal-root  ganglia,  the  ganglia 
of  certain  cranial  nerves,  etc.  The  nerve  centers  are  found  in  the  spinal  cord, 
the  medulla,  and  the  higher  cranial  groups.  The  medulla  is  particularly  rich 
in  nerve  centers.  The  cerebro-spinal  axis  is  in  fact  an  aggregation  of  nerve 
centers  of  greater  or  less  complexity. 

It  is  by  means  of  the  nerve  centers  that  the  activities  of  the  differentiated 
parts  of  the  human  body  are  brought  into  intimate  correlation.  The  nerve 
centers  exercise  their  influence  through  the  power  of  inhibiting  or  decreasing  ac- 
tivity; or,  on  the  other  hand,  of  augmenting  or  increasing  the  activity  in  the 
peripheral  tissues  or  in  other  parts  of  the  nervous  system.  For  example,  the 
vagus  center  regulates  the  activity  of  the  heart  muscle  by  its  power  to  decrease 
or  inhibit  cardiac  contractions.  This  center,  we  have  already  found,  is  in  con- 
stant tonic  activity;  that  is  to  say,  in  constant  regulative  control  of  the  heart. 
The  cardiac  augmentory  center,  on  the  other  hand,  produces  just  the  opposite 
effect,  increasing  the  activity  of  the  cardiac  muscle.  What  is  true  for  the  heart 
is  likewise  true  in  general  for  other  tissues  of  the  body.  The  numerous  nerve 
centers  in  the  central  nervous  svstem  are  brought  into  correlation  through  an 


NERVE     CENTERS 


509 


exceedingly  complex  system  of  communicating  fibers.  The  cerebro-spinal 
axis  may  in  fact  be  regarded  as  a  segmental  chain  of  nerve  centers,  the  com- 
plexity increasing  from  the  cord  toward  the  brain,  and  the  coordinating  con- 
trol culminating  in  the  cerebral  cortex. 


Fig.  357. — View  of  the  Cerebro-spinal  Axis  of  the  Nervous  System.  The  right  half  of  the 
cranium  and  trunk  of  the  body  has  been  removed  by  a  vertical  section;  the  membranes  of  the 
brain  and  spinal  cord  have  also  been  removed,  and  the  roots  and  first  part  of  the  fifth  and  ninth 
cranial,  and  of  all  spinal  nerves  of  the  right  side,  have  been  dissected  out  and  laid  separately  on 
the  wall  of  the  skull  and  on  the  several  vertebrae  opposite  to  the  place  of  their  natural  exit  from 
the  cranio-spinal  cavity       (After  Bourgery.) 


510  THE     NERVOUS    SYSTEM 


II.  THE  STRUCTURE  AND  FUNCTION  OF  THE 
SPINAL  CORD. 

STRUCTURE. 

The  spinal  cord  is  a  cylindrical  column  of  nerve-substance  connected  above 
with  the  brain  through  the  medium  of  the  bulb,  and  terminating  below  in  a 
slender  filament  of  nerve  substance,  the  filum  terminate,  which  lies  in  the  midst 
of  the  roots  of  the  many  nerves  forming  the  Cauda  equina. 

General  Features.  The  cord  is  composed  of  nerve  fibers  and  nerve 
cells.  The  former  are  situated  externally  and  constitute  the  chief  portion 
of  the  cord,  while  the  latter  occupy  its  central  or  axial  portion  and  are  so 
disposed  that  on  the  surface  of  a  transverse  section  of  the  cord  two  somewhat 
crescentic  grayish  masses  connected  by  a  narrower  portion  or  isthmus 
appear,  figure  358.  Passing  through  the  center  of  the  cord  in  a  longitudinal 
direction  is  a  minute  canal,  the  central  canal,  which  is  continued  through  the 
whole  length  of  the  cord,  opening  above  into  the  space  at  the  back  of  the 
medulla  oblongata  and  pons  Varolii  called  the  fourth  ventricle.  The  canal 
is  lined  by  a  layer  of  columnar  ciliated  epithelium. 

The  spinal  cord  consists  of  exactly  symmetrical  halves,  separated  anteriorly 
and  posteriorly  by  vertical  fissures  (the  posterior  fissure  being  deeper  but  less 
wide  and  distinct  than  the  anterior),  and  united  in  the  middle  by  nervous 
matter  which  forms  the  commissures.  The  central  part,  which  contains  the 
central  canal,  is  known  as  the  gray  commissure,  and  is  bounded  by  the  anterior 
white  commissure  in  front,  and  the  posterior  white  commissure  behind.  Each 
half  of  the  spinal  cord  is  marked  on  the  sides  (obscurely  at  the  lower  part,  but 
distinctly  above)  by  two  longitudinal  furrows,  which  divide  it  into  three  por- 
tions, columns,  or  tracts — an  anterior,  lateral,  and  posterior.  From  the  groove 
between  the  anterior  and  lateral  columns  spring  the  anterior  roots  of  the 
spinal  nerves;  and  just  in  front  of  the  groove  between  the  lateral  and 
posterior  columns  arise  the  posterior  roots  of  the  same;  a  pair  of  roots  on  each 
side  corresponding  to  each  vertebra. 

The  nerve  tracts  of  the  cord  are  made  up  of  medullated  nerve  fibers  of 
different  sizes,  arranged  longitudinally,  and  of  a  supporting  material  of  ordi- 
nary fibrous  connective  tissue  and  neuroglia,  figure  105. 

The  general  rule  respecting  the  size  of  different  segments  of  the  cord  appears 
to  be  that  each  is  in  direct  proportion  in  this  respect  to  the  size  and  number  of 
nerve  roots  given  off  from  it,  and  has  but  little  relation  to  the  size  or  number 
of  those  given  off  below  it.  Thus  the  cord  is  very  large  in  the  middle  and 
lower  part  of  its  cervical  portion,  whence  arise  the  large  nerve  roots  for  the 
formation  of  the  brachial  plexuses  and  the  nerve  supply  of  the  upper  extrem- 
ities;  and  again  enlarges  at  the  lowest  part  of  its  dorsal  portion  and  the  upper 


ARRANGEMENT   OF   NERVE    CELLS    IN   THE   SPINAL   CORD 


511 


part  of  its  lumbar,  at  the  origins  of  the  large  nerves  which,  after  forming  the 
lumbar  and  sacral  plexuses,  are  distributed  to  the  lower  extremities.  The 
chief  cause  of  the  greater  size  at  these  parts  of  the  spinal  cord  is  increase 
in  the  quantity  of  the  gray  matter;  for  there  seems  reason  to  believe  that  the 
white  part  of  the  cord  becomes  gradually  and  progressively  larger  from  below 
upward,  doubtless  from  the  addition  of  a  certain  number  of  ascending  fibers 
from  each  pair  of  nerves. 

From  careful  estimates  of  the  number  of  nerve  fibers  in  a  transverse  section 
of  the  cord  toward  its  upper  end,  and  the  number  entering  or  issuing  from  it 
by  the  anterior  and  posterior  roots  of  each  pair  of  nerves,  it  has  been  shown 


mm 


'\V*3fem 

M 


mm 


*T 


Fig.  358. — Horizontal  Section  of  the  Cord  and  its  Envelopes,  at  the  Middle  of  a  Vertebral  Body 
(Schematic).  1,  Spinal  cord  with  2,  its  anterior  median  fissure;  3,  its  posterior  median  fissure; 
4,  anterior  roots;  5,  posterior  roots;  6,  pia  mater  (in  red);  7,  ligamentum  dentatum;  8,  connect- 
ing fibers  passing  from  the  pia  to  dura  mater;  9,  visceral  layer,  and  9',  parietal  layer  of  the  arach- 
noid (in  blue),  10,  subarachnoid  space;  11,  arachnoid  cavity;  12,  dura  mater  (in  yellow);  13, 
periosteum;  13,'  external  periosteum;  14,  cellular  tissue  situated  between  the  dura  mater  and  the 
wall  of  the  vertebral  canal;  15,  common  posterior  vertebral  ligament;  16,  intraspinal  veins;  17, 
vertebra  in  section.      (Tesiut.) 

that  in  the  human  spinal  cord  not  more  than  half  of  the  total  number  of  nerve 
fibers  of  all  the  spinal  nerves  are  contained  in  a  transverse  section  near  its  upper 
end.  It  is  obvious,  therefore,  that  at  least  half  of  the  nerve  fibers  entering 
it  must  terminate  somewhere  in  the  cord  itself. 

The  Arrangement  of  Nerve  Cells  in  the  Spinal  Cord.  The  gray  mat- 
ter of  the  spinal  cord  consists  of  numerous  groups  of  nerve  cells  and  of  a 
close  meshwork  of  nerve  fibers,  most  of  which  are  very  fine  and  delicate. 
Medullated  fibers  mingled  with  the  small  gray  fibers  about  the  borders  of  the 


512 


THK     NERVOUS     SYSTEM 


gray  substance.  Mingled  with  it  and  supporting  it  is  the  meshwork  of  the 
neuroglia. 

The  multipolar  cells  of  the  cord  are  either  scattered  singly  or  arranged  in 
groups,  of  which  the  following  are  to  be  distinguished  on  either  side,  certain 
of  the  groups  being  more  or  less  marked  in  all  of  the  regions  of  the  cord,  viz., 
those,  a,  in  the  anterior  cornu,  b,  those  in  the  posterior  cornu,  and  c,  intrinsic 
cells  distributed  throughout  the  gray  matter. 

The  cells  in  the  anterior  cornu  are  large  and  branching,  and  each  gives  rise 
to  an  axis-cylinder  process  which  passes  out  in  the  anterior  nerve  root.     These 


Fig.  359. — From  the  Lower  Lumbar  Cord  of  Man,  after  a  Preparation  by  Klonne  and  Miiller, 
of  Berlin  (No.  11,153),  stained  by  Weigert  and  Pal's  method.  A  portion  of  the  gray  substance  of 
the  ventral  cornu  with  the  adjoining  portions  of  the  lateral  column  is  represented,  showing  an- 
terior-horn cells  and  the  fine  medullated  fibers  which  enter  the  gray  substance  from  the  lateral 
column  and  surround  the  nerve  cells,  which  here  are  provided  with  fine  pigmented  granules.  High 
power.      (Kolliker.) 


cells  are  everywhere  conspicuous,  but  are  particularly  numerous  in  the  cervi- 
cal and  lumbar  enlargements.  In  these  districts  they  may  be  divided  into 
several  groups:  i,  A  group  of  large  cells  close  to  the  tip  of  the  inner  part  of 
the  anterior  cornu — all  the  cells  of  the  anterior  cornu  in  the  dorsal  or  thoracic 
region  are  said  to  belong  to  this  group;  2,  several  lateral  groups,  2a,  2b,  and  2c, 
figure  360,  on  the  outer  side  of  the  gray  matter,  and  a  certain  number  of  cells  at 
the  base  of  the  inner  part  of  the  anterior  cornu  particularly  well  marked  in  the 
thoracic  region ;  3,  cells  of  the  posterior  cornu — these  are  not  numerous.    They 


ARRANGEMENT   OF    NERVE    CELLS    IN   THE    SPINAL   CORD 


513 


are  small  and  branched,  and  each  has  an  axis-cylinder  process  passing  eft"; 
but  these  processes  do  not  pass  into  the  posterior  nerve  roots.  The  groups 
are  two  at  least  in  number,  viz.,  a,  in  connection  with  the  edge  of  the  gray  matter 
externally,  where  it  is  considerably  broken  up  by  the  passage  of  bundles  of 
fibers  through  it,  and  called  the  lateral  reticular  formation  ;  and  b,  in  connection 
with  a  similar  reticular  formation,  more  at  the  tip  of  the  gray,  known  as  the 
posterior  reticular  formation. 

A  group  of  cells,  3,  figure  360,  is  situated  at  the  base  and  median  side  of  the 
posterior  cornu.  It  is  formed  of  fairly  large  cells,  fusiform  in  shape,  and 
constitutes  the  posterior  vesicular  column,  or  Clarke's  column.  It  extends 
from  the  seventh  cervical  to  the  third  lumbar  segment.  On  the  outer  por- 
tion of  the  gray  matter,  midway  between  the  anterior  and  posterior  cornua, 


Fig.  360.— Section  of  Spinal  Cord.  One  Half  of  Which  (Left)  Shows  the  Tracts  of  the  White 
Matter,  and  the  Other  Half  (Right)  Shows  the  Position  of  the  Nerve  Cells  in  the  Gray  Matter.  7, 
10,  9,  and  3  are  tracts  of  descending  degeneration;  1,4,  6  and  8,  of  ascending  degeneration.  Semi- 
diagrammatic.      (After  Sherrington.) 


is  a  group  of  cells,  known  as  the  cells  of  the  lateral  gray  column.  These  are 
small  and  spindle-shaped,  and  are  more  or  less  marked  in  the  lumbar  region, 
as  well  as  in  the  thoracic  region,  5,  figure  360. 

Besides  these  groups,  which  have  their  names  largely  on  account  of  their 
location,  there  are  distributed  throughout  the  gray  matter  a  very  large  number 
of  other  cells,  which  are  known  as  intrinsic  cells.  These  send  out  axones 
which  pass  into  the  adjacent  ground  bundles  of  the  same  or  of  the  opposite 
side,  and  pass  up  and  down  the  cord,  to  enter  the  gray  matter  again.  They 
connect  bv  their  end-brushes  with  cells  at  different  levels  of  the  cord. 

The  function  of  these  connecting  cells,  or  intrinsic  cells,  is  to  unite  the  pos- 
terior and  anterior  regions  of  the  cord,  to  serve  as  conductors  between  the 
lateral  halves,  or  to  connect  segments  at  different  levels.  They  are  also  dis- 
33 


514 


THE     NERVOUS     SYSTEM 


tributing  fibers  in  that  they  bring  a  single  or  at  least  a  small  number  of  pos- 
terior neurones  into  connection  with  a  relatively  large  number  of  anterior  neu- 
rones. 

Columns  and  Tracts  in  the  White  Matter  of  the  Spinal  Cord.  In 
addition  to  the  columns  of  the  white  matter  which  are  marked  out  by  the 
points  from  which  the  nerve  roots  issue,  and  which  are  the  anterior,  the  lateral, 
and  posterior,  the  posterior  is  further  divided  by  a  septum  of  the  pia  mater  into 


Radix  anterior 
Fasciculus  cerebrospinalis  lateralis  [pyTaniidalis  lateralis)    > 
Anterior  root  fibre 
Bundle  to  anterior  funiculus  from  the  formatio  reticularis 
Fasciculus  cerebrospinalis  anterior 
[pyramidalis  anterior}        \ 

Bundle  to  anterior  funiculus 
from  the  formatio  reticularis 


Substantia  grisca.  — > 


Fasciculus 

anterolateralis  super- 

ficialis   (Gowersi)  and 

(ascending)  bundle  from 

anterior  funiculus  to  the 

formatio  reticularis 

Substantia  alba 

Bundle'  to  lateral 
funiculus  from  Deiters' 
nucleus   and  from  "tho 
red  nucleus . 


Fasciculus  eerebro 

spinalis  lateralis 

(pyramidalis  laterali 


Nervus  spinalis 

Ganglion  spinale 
Cells  of  tho  spinal  ganglion 
..  Fasciculus  cerebellospinalis 
s  Secondary  reflex  path 

„  Radix  posterior 

Collateral 
i-  to  the  posterior  horn 
Jf     Secondary  path  of 
r~-  posterior  funiculus 

descending  posterior 

root  fibre 
Primary  reflex  path 

-•■Ascending  posterior 
root  fibre 

>  Secondary  reflex  path 


.Descending  posterior 
root  fibro 


Posterior  loot  fibre 


Sulcus  rnedianus 
posterior 


'- Posterior  root  fibre 


Fig.  361. — Reconstruction  of  a  Segment  of  the  Spinal  Cord  Representing  Both  a  Transverse 
and  Longitudinal  Section.      (Held,  from  Spalteholz's  Anatomy.) 


two  almost  equal  parts,  constituting  the  postero-extemal  column,  or  column  of 
Burdach,  figure  360,  2,  and  the  poster o-median,  or  column  oj  Goll.  In  addition 
to  these  columns,  however,  it  has  been  shown  that  the  white  matter  can  be  still 
further  subdivided.  This  subdivision  has  been  accomplished  by  evidence  of 
several  kinds  that  the  parts  or,  as  they  are  called,  tracts  in  the  white  matter 
perform  different  functions  in  the  conduction  of  impulses. 

The  methods  of  observation  are  the  following: 

The  embryological  method.  It  has  been  found  that,  if  the  development 
of  the  spinal  cord  be  carefully  observed  at  different  stages,  certain  groups  of 


TRACTS     OF     DESCENDING     DEGENERATION  515 

the  nerve  fibers  acquire  their  myelin  sheath  at  earlier  periods  than  others, 
and  that  the  different  groups  of  fibers  can  therefore  be  traced  in  various 
directions.     This  is  known  as  the  method  of  Flechsig. 

Wallerian  or  degeneration  method.  This  method  depends  upon  the  fact 
already  presented  that  if  a  nerve  fiber  is  separated  from  its  nerve  cell  it  wastes 
or  degenerates.  It  consists  in  tracing  the  course  of  tracts  of  degenerated 
fibers  which  result  from  an  injury,  to  any  part  of  the  central  nervous  system. 
When  fibers  degenerate  below  a  lesion  the  tract  is  said  to  be  of  descending 
degeneration,  and  when  the  fibers  degenerate  in  the  opposite  direction  the  tract 
is  one  of  ascending  degeneration.  By  modern  methods  of  staining  of  the  cen- 
tral nervous  system  it  has  proved  comparatively  easy  to  distinguish  degener- 
ated parts  in  sections  of  the  cord  and  of  other  portions  of  the  central 
nervous  system.  Degenerated  fibers  have  a  different  staining  reaction 
when  the  sections  are  treated  by  what  are  called  Weigert's  and  Marchi's 
methods.  Accidents  to  the  central  nervous  system  in  man  have  given  us  much 
information  as  to  its  organization,  but  this  has  of  late  years  been  supplemented 
and  largely  extended  by  the  experiments  on  animals,  particularly  upon 
monkeys.  Considerable  light  has  by  the  method  of  section  and  degeneration 
been  shed  upon  the  path  of  conduction  of  impulses  to  and  from  the  nervous 
system.  Thus  we  not  only  have  embryological  evidence  mapping  out  different 
tracts,  but  also  confirmatory  pathological  and  experimental  observations. 

The  tracts  which  have  been  made  out  are  the  following: 

Tracts  of  Descending  Degeneration.  The  Crossed  Pyramidal  Tract. 
This  tract  is  situated  to  the. outer  side  of  the  posterior  cornu  of  gray 
matter,  figure  360,  7.  It  is  found  throughout  the  whole  length  of  the  spinal 
cord;  at  the  lower  part  it  extends  to  the  margin  of  the  cord,  but  higher 
up  it  becomes  displaced  inward  from  this  position  by  the  interpolation  of 
another  tract  of  fibers,  the  direct  cerebellar  tract.  The  crossed  pyramidal 
tract  is  large,  and  may  touch  the  tip  of  the  gray  matter  of  the  posterior  cornu, 
but  it  is  separated  from  it  elsewhere.  It  is  oval  in  shape  on  cross-section,  and 
diminishes  in  size  from  the  cervical  region  downward.  The  tract  is  particu- 
larly well  marked  out,  both  by  the  degeneration  and  the  embryological  methods. 
The  fibers  are  supposed  to  pass  off  as  they  descend,  and  to  join  the  various 
local  nervous  mechanisms  of  nerve  cells  and  their  branchings  which  are  rep- 
resented in  the  cord.  The  tract  of  degeneration  may  be  traced  upward  beyond 
the  cord,  in  a  way  to  be  presently  described.  The  fibers  of  which  this  tract 
is  composed  are  moderately  large,  but  are  mixed  with  some  that  are  smaller. 

The  Direct  or  Uncrossed  Pyramidal  Tract.  This  tract  is  situated  in  the 
anterior  column  by  the  sides  of  the  anterior  fissure,  figure  360,  10.  It  is  smaller 
than  the  crossed  tract  and  is  not  present  in  all  animals,  though  conspicuous 
in  the  human  cord  and  in  that  of  the  monkey.  It  can  be  traced  upward  to 
the  cerebral  cortex,  and  downward  as  far  as  the  mid  or  lower  thoracic  region, 
where  it  ends. 


,,1<>  THE     NERVOUS     SYSTEM 

Antero-lateral  Descending  Tract.  This  is  an  extensive  tract,  elongated 
but  narrow,  and  reaching  from  the  crossed  to  the  direct  pyramidal  tract.  It  is 
a  mixed  tract,  since  not  all  of  its  fibers  degenerate  below  the  lesions. 

Comma  Tract.  This  is  a  small  tract  of  fibers  which  degenerate  below 
the  point  of  section  or  injury  of  the  cord.  Its  presence  has  been  demonstrated 
in  the  cervical  and  thoracic  regions.  It  is  supposed  to  consist  of  the  descending 
collaterals  of  the  posterior  nerve  roots  as  they  pass  into  the  postero-external 
columns. 

Tracts  of  Ascending  Degeneration.  Postero -median  Column  and 
Postero-lateral  Column.  These  tracts  degenerate  upward  on  injury  or 
on  section  of  the  cord,  also  on  section  of  the  posterior  nerve  roots,  figure  360, 
1.  They  exist  throughout  the  whole  of  the  cord  from  below  up,  and  can  be 
traced  into  the  bulb.     They  consist  of  fine  fibers. 

Direct  Cerebellar  Tract.  This  tract  is  situated  on  the  outer  part  of  the  cord 
between  the  crossed  pyramidal  tract  and  the  margin.  It  is  found  in  the  cervi- 
cal, thoracic,  and  upper  lumbar  regions  of  the  cord,  and  increases  in  size 
from  below  upward.  It  degenerates  on  injury  or  section  of  the  cord  itself, 
but  not  on  section  of  the  posterior  nerve  roots,  since  its  fibers  arise  from  the 
cells  of  Clarke's  column.  As  its  name  implies,  it  is  believed  to  pass  up  into 
the  cerebellum. 

Antero-lateral  Ascending  Tract,  Tract  oj  Gowers,  figure  360,  8.  This 
tract  has  been  shown  on  injury  to  the  spinal  cord ;  it  is  situated  at  the  margin 
of  the  cord  outside  of  the  corresponding  descending  tract.  It  is  traceable 
throughout  the  whole  length  of  the  cord. 

Tract  oj  Lissauer,  or  Posterior  Marginal  Zone.  A  small  tract  of  fine  white 
fibers,  situated  at  the  apex  of  the  posterior  horn,  is  made  up  of  fibers  from 
the  posterior  nerve  roots  which  enter  the  column  and  pass  up  and  down 
for  a  short  distance,  finally  entering  the  posterior  horn,  where  they  terminate 
in  fine  end-brushes  around  the  cells  of  the  posterior  horn. 

It  will  thus  be  seen  that  the  white  matter  of  the  spinal  cord  has  three  gen- 
eral divisions — into  the  anterior,  the  lateral,  and  posterior  columns.  These 
columns  are  subdivided  into  tracts  in  which  the  fibers  degenerate  upward, 
those  in  which  the  fibers  degenerate  downward,  and  others  in  which  the  fibers 
degenerate  neither  way  except  for  short  distances  when  the  cord  is  cut  across. 
These  parts  cf  the  cord  are  composed  of  commissural  fibers  which  connect 
different  levels  cf  the  cord.  The  commissural  tracts  form  the  antero-lateral 
columns  and  the  lateral  limiting  layer.  The  arrangement  of  these  tracts  is 
shown  well  in  figure  360. 

The  Spinal  Nerves.  The  spinal  nerves  consist  of  thirty-one  pairs, 
from  the  sides  of  the  whole  length  of  the  cord,  their  number  corresponding 
with  the  intervertebral  foramina  through  which  they  pass.  Each  nerve  arises 
by  two  roots,  an  anterior  and  a  posterior,  the  latter  being  the  larger. ,  The  roots 
emerge  through  separate  apertures  of  the  sfieath  of  dura  mater  surrounding 


COUBSE   OF   THE    FIBERS    OF   THE    SPINAL    NERVE    ROOTS 


517 


the  cord;  and  directly  after  their  emergence,  where  the  roots  lie  in  the  inter- 
vertebral foramen,  a  ganglion  is  found  on  the  posterior  root.  The  anterior 
root  lies  in  contact  with  the  anterior  surface  of  the  ganglion,  but  none  of  its 
fibers  intermingle  with  those  in  the  ganglion,  figure  361.  But  immediately 
beyond  the  ganglion  the  two  roots  coalesce,  and  by  the  mingling  of  their  fibers 
form  a  compound  or  mixed  spinal  nerve,  which,  after  issuing  from  the  inter- 
vertebral canal,  gives  off  anterior  and  posterior  (or  ventral  and  dorsal)  branches, 
each  containing  fibers  from  both  the  roots  as  well  as  a  third  or  visceral 
branch,  ramus  communicans,  to  the  sympathetic. 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous  separate  and 
converging  bundles  from  the  anterior  column  of  the  cord;   the  posterior  root 


Entering  posterior 
root 

Lissauer's  tract 


Emerging  anterior  root 


Fig.  362. — Diagrammatic  Transverse  Section  of  the  Spinal  Cord,  Showing  the  Conduction  Paths 
and  Groups  of  Cells.      (Cunningham.) 


by  more  numerous  parallel  bundles,  from  the  posterior  column,  or,  rather, 
from  the  posterior  part  of  the  lateral  column,  for  if  a  fissure  be  directed 
inward  from  the  groove  between  the  middle  and  posterior  columns,  the  pos- 
terior roots  will  remain  attached  to  the  former.  The  anterior  roots  of  each 
spinal  nerve  consist  chiefly  of  efferent  fibers;  the  posterior  exclusively  of 
afferent  fibers. 

Course  of  the  Fibers  of  the  Spinal  Nerve  Roots.  The  Anterior 
Roots.  The  anterior  roots  leave  the  cord  in  several  bundles,  which  may  be 
called:  1,  Internal;  2,  Middle;  3,  External.  All  have  their  origin  from  the 
groups  of  multipolar  cells  in  the  anterior  cornua.  The  internal  fibers  are 
originated  partly  in  the  internal  group  of  nerve  cells  of  the  anterior  cornu 


518 


THE     NERVOUS     SYSTEM 


of  the  same  side;    but  some  fibers  can  be  traced  through  the  anterior  com- 
missure to  cells  of  the  anterior  cornu  of  the  opposite  side. 

The  Posterior  Roots.  The  fibers  of  the  posterior  roots  enter  the  spinal 
cord  to  the  inner  or  median  side  of  the  posterior  cornu.  The  fibers, 
as  soon  as  they  reach  the  cord,  divide  in  a  fork-like  fashion,  one  branch 
passing  down  a  short  distance,  about  three  centimeters,  the  other  branch 
passing  up  for  a  shorter  or  longer  distance.  This  upper  branch  some- 
times reaches  the  whole  extent  of  the  cord,  but  generally  it  extends  over 
only  one  or  two  segments  of  the  cord.  The  divisions  of  the  posterior  root 
fibers  give  off  in  their  course  numerous  collaterals,  figure  368.     The  fibers 


FlG.  363. — Section  of  the  Spinal  Cord,  Showing  the  Grouping  of  Nerve-Cells  and  the  Course  of 
Nerve  Fibers  Entering  in  Posterior  and  Anterior  Roots.      (After  Lenhossek.) 


of  the  posterior  roots  are  divided  into  two  sets,  an  internal  or  median,  an  ex- 
ternal or  lateral  group.  The  lateral  set  consists  mostly  of  small  fibers  which 
enter  the  cord  opposite  the  tip  of  the  posterior  horn.  The  fibers  pass  in  part 
to  the  marginal  column  of  Lissauer,  where  they  ascend  and  descend;  in  part 
they  penetrate  the  posterior  horn,  and  come  in  relation  with  its  cells.  From 
the  median  set  some  fibers  pass  to  Clarke's  column,  others  pass  by  way 
of  the  posterior  commissure  to  the  median  cells  of  the  other  side.  Others 
pass  through  the  gray  matter  to  the  anterior  horn  cells  of  the  same  side. 
Besides  this,  they  are  connected  through  collaterals  with  the  intrinsic  cells  of 
the  gray  matter  at  different  levels  of  the  cord.  One  can  realize  that  each 
nerve  root  has,  in  this  way,  an  effective  grip  upon  a  large  extent  of  the  cord. 
This  is  seen  well  by  studying  figures  361  and  363. 


THE    REFLEX    ARC    AND     REFLEX    ACTION  519 

The  Peculiarities  of  Different  Regions  of  the  Spinal  Cord.     The 

outline  of  the  gray  matter  and  the  relative  proportion  of  the  white  matter 
vary  in  different  regions  of  the  spinal  cord,  and  it  is,  therefore,  possible  to 
tell  approximately  from  what  region  any  given  transverse  section  of  the 
spinal  cord  has  been  taken.  The  white  matter  increases  in  amount  from 
below  upward.  The  amount  of  gray  matter  varies;  it  is  greatest  in  the 
cervical  and  lumbar  enlargements,  viz.,  at  and  about  the  5th  lumbar  and  the 
6th  cervical  nerves,  and  least  in  the  thoracic  region.  The  greatest  develop- 
ment of  gray  matter  corresponds  with  greatest  number  of  nerve  fibers 
passing  from  the  cord. 

In  the  cervical  enlargement  the  gray  matter  occupies  a  large  proportion  of 
the  section,  the  gray  commissure  is  short  and  thick,  the  anterior  horn  is  blunt, 
while  the  posterior  is  somewhat  tapering.  The  anterior  and  posterior  roots 
run  some  distance  through  the  white  matter  before  they  reach  the  periphery. 

In  the  dorsal  region  the  gray  matter  bears  only  a  small  relation  to  the  white, 
and  the  posterior  roots  in  particular  run  a  long  course  through  the  white  matter 
before  they  leave  the  cord;  the  gray  commissure  is  thinner  and  narrower  than 
in  the  cervical  region. 

In  the  lumbar  enlargement  the  gray  matter  again  bears  a  very  large  propor- 
tion to  the  whole  size  of  the  transverse  section,  but  its  posterior  cornua  are 
shorter  and  blunter  than  they  are  in  the  cervical  region.  The  gray  commissure 
is  short  and  extremely  narrow. 

At  the  upper  part  of  the  conns  medullaris,  which  is  the  portion  of  the  cord 
immediately  below  the  lumbar  enlargement,  the  gray  substance  occupies  nearly 
the  whole  of  the  transverse  section,  as  it  is  invested  only  by  a  thin  layer  of 
white  substance.  This  thin  layer  is  wanting  in  the  neighborhood  of  the 
posterior  nerve  roots.     The  gray  commissure  is  extremely  thick. 

At  the  level  0}  the  fifth  sacral  vertebra  the  gray  matter  is  again  in  excess,  and 
the  central  canal  is  enlarged,  appearing  T-shaped  in  section;  while  in  the 
tipper  portion  of  the  filum  terminable  the  gray  is  uniform  in  shape  without  any 
central  canal. 

The  Reflex  Arc  and  Reflex  Action.  The  spinal  cord  is  morpho- 
logically a  segmental  or  metameric  structure.  This  is  shown  both  by  its 
development  and  by  its  comparative  anatomy.  The  pairs  of  nerves  are 
indicative  of  the  component  segments  of  the  cord.  The  tracts  of  the  cord  are 
in  a  sense  connectives  from  segment  to  segment,  connecting  the  cells  of 
both  adjacent  and  of  widely  separated  segments.  The  function  of  the  cord 
is  comprised  in  the  function  of  the  segments  and  in  the  function  of  the  tracts. 

From  a  physiological  point  of  view,  it  may  almost  be  considered  as  an 
axiom  that  before  a  nerve  cell  can  send  out  a  nerve  impulse  it  must  first 
receive  a  stimulus  of  some  kind.  This  stimulus  usually  consists  of  an  afferent 
impulse  from  the  periphery.  Its  effect  upon  the  receiving  cell  may  be  insuf- 
ficient to  cause  any  response,  or  the  response  may  be  delayed  for  a  long  period 


520 


THE     NERVOUS     SYSTEM 


and  may  involve  manv  complicated  nervous  activities  and  even  psychological 
processes.  Where  the  response  is  approximately  immediate,  the  reaction  is 
known  as  a  reflex. 

A  reflex  arc,  reduced  to  its  simplest  terms,  consists  of  the  following  ele- 
ments: a,  a  sensory  surface;  b,  an  afferent  neurone;  c,  an  efferent  neurone;  d, 


Fig.  364. — Schematic  Sketch  of  a  Reflex  Arc.    A ,  With  two  neurones,  an  afferent  and  an  efferent; 
B,  with  three  neurones,  an  afferent,  efferent,  and  a  connecting  or  intracentral  neurone. 


a  muscle  or  gland.     The  simplest  form  of  reflex  arc  is  schematically  shown 

in  figures  364  and  365. 

The  gap  between  the  termination  of  the  afferent  neurone  and  the  dendron 

of  the  efferent  neurone  shown  in  figure  364  is  called  a  synapsis.    The  reflex  arc  is 

probably  seldom  as  simple  as  that  shown  in  figure  365,  where  only  two  neurones 

are  involved.  More  often,  three  or  more 
neurones  take  part,  as  shown  in  figures  364  B, 
and  366. 

The  neurone  connecting  the  afferent 
neurone  with  the  efferent  neurone  belongs 
to  the  class  of  intracentral  or  connecting 
neurones.  Since  all  parts  of  the  cord,  in 
fact  of  the  entire  cerebro-spinal  axis,  are  in- 
directly connected  with  one  another  by 
intracentral  neurones,  figure  361,  the  possi- 
bility of  increasing  the  number  of  efferent 
limbs  of  the  reflex  arc  can  be  readily  under- 
stood. 

A  physiological  reaction  in  a  tissue  pro- 
duced by  efferent  nerve  impulses  which  have 
been  discharged  from  a  nerve  center  under 
the  stimulus  of  a  sensory  or  afferent  nerve 
impulse,  is  called  a  reflex  act.  Where  the 
nervous  apparatus  involved  is  of  the  type 
represented  in  figures  364  and  365,  the  activ- 
ity is  called  a  simple  reflex.     Most  reflexes 


mw. 


mw, 


Fig.  365. — Showing  the  Arrangement 
of  a  Simple  Reflex  Mechanism  Composed 
of  a  Motor  and  Sensory  Neurone,  sg, 
Posterior  spinal  ganglion;  s  and  sth,  sen- 
sor" root;  m,  motor-nerve  cell;  mw, 
motor  root.      (Kolliker.) 


IRRADIATION     OF     IMPULSES    WITHIN     THE    CORD 


521 


are  more  complex  in  character.  The  afferent  nerve  impulse  passes  through 
more  than  one  simple  channel  in  the  cord,  so  that  a  series  of  coordinated 
acts  occurs  in  what  may  be  called  a  complex  reflex. 

The  transmission  of  impulses  within  the  cord  occurs  over  the  pathways 
of  least  resistance.  Increasing  the  number  of  synapses,  or  the  number  of 
neurone  links'  in  the  chain  of  conduction,  increases  the  resistance  so  that  re- 
flexes will  occur  most  readily,  other  conditions  being  equal,  where  the  least 
number  of  neurones  is  involved,  i.e.,  in  the  same  segment  of  the  cord  in  which 
ihe  sensory  impulse  enters,  or  in  immedi- 
ately adjacent  segments.  In  addition  to  the 
number  of  synapses  in  the  reflex  arc,  other 
factors  are  of  importance  in  determining  reflex 
reaction;  e.g.,  the  intensity  of  the  exciting 
stimulus;  the  quality  of  the  stimulus;  the 
rapidity  of  the  recurrence  of  the  stimulus; 
and  the  duration  of  its  application.  Thus, 
a  strong  stimulus  will  bring  about  a  reflex 
reaction  sooner  than  a  weak  stimulus  of  the 
same  kind.  A  single  weak  stimulus  which 
will  cause  no  reflex  may  do  so  if  often  enough 
and  rapidly  enough  repeated,  the  phenomenon 
of  summation  0}  stimuli. 

A  reflex  act  once   started   may  result  in 
efferent   impulses   which  continue   for   some 

time  after  the  exciting  cause  has  been  removed.  The  same  phenomenon 
is  observed  where  groups  of  nerve  cells  are  stimulated  directly.  It  has  been 
found,  by  observing  electrical  changes  in  nerve  fibers  by  means  of  the  capillary 
electrometer,  that  when  their  cells  of  origin  are  stimulated  they  discharge  im- 
pulses in  a  rhythmical  manner. 

Usually,  impulses  are  transmitted  to  a  nerve  cell  only  over  its  dendrons, 
but  it  must  be  also  assumed  that  such  a  conveyance  of  impulses  may  take  place 
over  the  collaterals  of  its  axone  near  the  cell  body,  or  the  cell  body  may  be 
stimulated  directly  by  the  afferent  neurone.  The  peripheral  fiber  of  the 
spinal  ganglion  cell,  although  it  has  the  structure  of  an  axone,  may  be  looked 
upon  physiologically  as  a  dendron,  since  homologues  in  lower  vertebrates  and 
in  man  himself  (olfactory-nerve  cells)  have  this  structure,  the  nerve  cell  body 
being  situated  near  the  sensory  surface  from  which  impressions  are  received. 

Irradiation  of  Impulses  within  the  Cord.  Taking  as  an  example  a 
frog  whose  brain  has  been  destroyed,  a  simple  reflex  may  be  demonstrated  by 
irritating  the  skin  of  one  foot  with  a  weak  stimulus.  In  response  to  such  a 
stimulus  the  foot  is  flexed  upon  the  leg,  due  to  a  contraction  of  the  muscles  of 
the  reflex  arc  corresponding  to  the  sensory  surface  irritated.  If  the  strength  or 
duration  of  the  stimulus  be  increased,  other  groups  of  muscles  are  involved 


Fig.  366. — Showing  the  Arrange- 
ment of  the  Reflex  Mechanism,  with 
a  Neurone  Intercalated  between  the 
Sensory  and  Motor  Neurones. 


522 


THE    NERVOUS     SYSTEM 


in  the  following  order:  r,  Those  of  the  leg  and  thigh  of  the  same  side;  2, 
homologous  muscles  of  the  opposite  side;  3,  the  arms  of  the  same  side  and  of 
the  opposite  side. 

The  increasing  complexity  of  the  reflexes  aroused  by  stimulation  of  one  and 
the  same  sensory  spot  is  not  easy  of  explanation.     We  know  that  there  is  almost 

an  infinite  number  of  morphological  paths  in 
the  cord,  yet  the  responses  are  orderly  and 
observe  a  certain  sequence  in  their  increasing 
complexity.  The  reflexes  have  a  mechanical 
definiteness  which,  in  a  living  structure,  seems 
almost  purposeful,  yet  there  is  no  conscious- 
ness in  a  frog  which  has  its  brain  destroyed. 

The  fact  is  that  in  the  development  of  the 
nervous  system  certain  physiological  paths  of 
slight  resistance  have  been  established  between 
the  sensory  areas  and  the  muscles  which  move 
the  parts  for  their  protection.  Apparently 
othor  physiological  nerve  pathways  exist,  but 
it  requires  a  stronger  sensory  stimulus  to 
arouse  nerve  impulses  along  these  paths.  In 
explanation  we  may  suppose  that  the  stronger 
afferent  impulses  are  sufficient  to  overcome 
the  resistance  of  increasingly  complex  paths, 
that  they  diffuse  through  greater  and  greater 
extents  of  the  cord.  But  we  may  repeat  that 
in  the  normal  state  of  the  cord  this  diffusion  is 
in  an  orderly  physiological  sequence. 

Orderly  reflexes  can  be  called  forth  only 
by  stimulating  sensory  nerve  endings,  the 
first  of  the  essential  structures  of  the  reflex  arc. 
If  artificial  stimuli  are  applied  to  a  nerve 
trunk,  as  the  sciatic,  uncoordinated  muscular 
responses  occur  because  the  sensory  stimuli 
are  diffuse  and  general  and  are  not  specific 
and  local. 

An  involvement  of  multiple  pathways  may 
also  be  accomplished  through  decreasing  the 
resistance  within  the  cord,  as  through  the  use 
of  some  drug  such  as  strychnine.  In  the 
strychninized  frog  a  slight  stimulus  brings 
about  multiple  and  violent  reflex  spasms. 
These  contractions  have  lost  their  orderliness  and  are  uncoordinated.  The 
entire  musculature  contracts.      It  is  as  though  the  strychnine  removed  all 


Fig.  367. — Scheme  of  Lower  Mo- 
tor Neurone.  The  cell  body,  proto- 
plasmic processes,  axone,  collaterals, 
and  terminal  arborizations  in  muscle 
are  all  seen  to  be  parts  of  a  single  cell 
and  together  constitute  the  neurone. 
(Barker.)  c,  Cytoplasm  of  cell  body 
containing  chromophilic  bodies,  neu- 
rofibrils, and  perifibrillar  substance; 
n,  nucleus;  n' ,  nucleolus;  d,  den- 
drites; ah,  axone  hill  free  from  chro- 
mophilic bodies;  ax,  axone;  sf,  side 
fibril  (collateral);  m,  medullary 
sheath;  nR,  node  of  Ranvier  where 
side  branch  is  given  off;  si,  neu- 
rilemma and  incisures  of  Schmidt; 
m,  striated  muscle  fiber;  tel,  motor 
end  plate. 


FUNCTIONS     OF    THE     SPINAL    NERVE     ROOTS  523 

differences  in  the  facility  with  which  afferent  stimuli  spread  through  the  cord, 
and  that  the  resistance  was  reduced  to  the  minimum.  The  strychnine  effect 
is  possibly  due  to  a  decrease  in  the  resistance  at  the  synapses,  and  possibly 
also  to  an  increase  in  the  irritability  of  the  discharging  nerve  cells. 

We  must  also  suppose  that  the  centers  are  particularly  sensitive  to  certain 
kinds  of  stimuli,  sometimes  producing  very  extensive  and  violent  muscular 
actions  in  response  to  a  slight  stimulus  of  a  special  kind.  Such  a  condition 
is  illustrated  in  the  violent  and  general  muscular  spasms  occurring  when  a 
small  particle  of  food  passes  into  the  larynx,  violent  expiratory  spasms  ac- 
companied by  contractions  of  other  muscles  taking  place. 

The  time  taken  in  a  reflex  action  for  the  eye  in  man  has  been  found  to  be 
0.066  to  0.058  of  a  second,  but  this  estimate  includes  the  entire  time  from 
the  instant  of  stimulation  to  the  beginning  of  the  contraction  of  the  muscle. 

Functions  of  the  Spinal  Nerve  Roots.  The  anterior  spinal  nerve 
roots  are  efferent  in  function  and  the  posterior  are  afferent.  The  fact  is 
proved  in  various  ways.  Division  of  the  anterior  roots  of  one  or  more  nerves 
is  followed  by  complete  loss  of  motion  in  the  parts  supplied  by  the  fibers  of 
such  roots,  but  the  sensation  of  the  parts  remains  perfect.  Division  of  the 
posterior  roots  destroys  the  sensibility  of  the  parts  supplied  by  their  fibers, 
while  the  power  of  motion  continues  unimpaired.  Moreover,  stimulation  of 
the  ends  of  the  distal  portions  of  the  divided  anterior  roots  of  a  nerve  excites 
muscular  movements.  There  are  sometimes  slight  evidences  of  sensory  im- 
pulses due  to  recurrent  fibers  that  are  distributed  through  the  anterior  root 
to  the  spinal  meninges.  Stimulation  of  the  proximal  ends  of  the  anterior 
roots,  which  are  still  in  connection  with  the  cord,  is  followed  by  no  appreciable 
effect.  It  must  be  remembered,  however,  that  in  the  anterior  or  efferent  nerves 
other  fibers  besides  motor  are  contained,  e.g  ,  vaso-motor,  secretory,  heat  fibers, 
and  when  the  distal  end  of  a  divided  nerve  is  stimulated,  the  effects  are  ex- 
ercised not  only  upon  muscles,  but  upon  glands,  blood-vessels,  etc.  Stimu- 
lation of  the  distal  portions  of  the  divided  posterior  roots,  on  the  other  hand, 
produces  no  muscular  movements  and  no  manifestations  of  pain;  for,  as  al- 
ready stated,  sensory  nerves  convey  impressions  only  toward  the  nerve  cen- 
ters. Stimulation  of  the  proximal  portions  of  these  roots  elicits  signs  of  in- 
tense suffering.  Muscular  movements  also  ensue;  but  these  are  the  result 
of  the  reflex  stimulation  of  the  motor  neurones  of  the  anterior  horn  of  the  cord 
or  are  movements  in  response  to  the  afferent  impulses  passing  to  higher  centers 
from  the  roots  stimulated. 

Functions  of  the  Ganglia  on  Posterior  Roots.  The  cells  of  the  posterior 
ganglia  act  as  centers  for  the  nutrition  of  the  nerve  fibers  given  off  from  them. 
When  these  are  cut,  the  parts  of  the  nerves  so  severed  degenerate,  while  the 
parts  which  remain  in  connection  with  the  cells  of  the  ganglia  do  not.  Thus 
on  section  of  the  posterior  nerve  root  beyond  the  ganglion  the  peripheral  part 
degenerates  and  the  central  does  not,  and  on  section  of  the  root  between 


524 


THE     NERVOUS     SYSTEM 


the  ganglion  and  the  cord  the  central  part  degenerates  and  the  peripheral 
is  unaffected. 

Spinal  Reflexes  in  Man  and  Mammals.  Much  of  our  knowledge  of 
the  reflexes  of  the  cord  is  derived  from  experiments  on  dogs,  though  paral- 
ysis of  the  lower  extremities  in  man,  by  accident  or  otherwise,  has  given  con- 
firmatory information.  In  man  the  spinal  cord  is  so  much  under  the  control 
of  the  higher  nerve  centers  that  its  own  individual  functions  in  relation  to  re- 
flex action  are  apt  to  be  overlooked.  But  if  the  skin  of  the  foot  is  stimulated,  in 
a  man  whose  lumbar  cord  is  completely  separated  by  injury  or  disease,  the 


Fig.  368. — Scheme  of  the  Relation  of  the  Posterior  Root  Fibers  upon  Entering  the  Cord.  A ,  The 
branch  of  the  dorsal  root  fibers  upon  entering  cord;  B,  terminal  arborization  about  cell  bodies 
of  the  cord;  DR,  axones  of  the  dorsal  root  ;  B,  their  ascending  and  descending  branches;  C, 
collaterals.      (After  Cajal.) 


foot  will  be  drawn  away  from  the  stimulus;  or,  if  the  stimulus  be  strong 
enough,  the  entire  leg  will  be  moved.  In  both  cases  the  movement  may  be 
orderly  and  well  coordinated,  and  shows  that  the  sensory  stimulus  has  pro- 
duced a  coordinated  reflex  through  the  lumbar  cord.  The  injured  person 
feels  no  sensation  of  pain  nor  of  action,  and  the  phenomenon  is  independent 
of  the  higher  nerve  regions.  The  stimulus  that  is  applied  to  man  must  be 
carefully  graded,  since  when  too  intense  it  calls  forth  muscular  spasms  or 
convulsive  action. 


SPINAL    REFLEXES    IN    MAX     VXD    MAMMALS  525 

When  the  cord  is  first  cut,  the  shock  is  very  great,  the  lower  or  isolated 
portion  of  the  cord  remains  for  a  time  quite  non-irritable.  The  vaso-motor  and 
thermogenic  centers  are  cut  off  so  that  there  is  great  vascular  dilatation  and 
marked  fall  of  temperature,  the  effects  of  which  are  likely  to  lead  to  death 
unless  the  operated  animal  is  carefully  attended.  But  these  effects  are  slow- 
ly recovered  from,  and  man,  as  well  as  lower  mammals,  soon  regains  the 
vascular  tone.  The  general  tonus  of  the  muscular  system,  which  is  lost  at  first, 
is  also  regained. 

In  this  partially  recovered  condition  man,  and  such  animals  as  the  cat,  the 
dog,  and  the  monkey,  perform  certain  of  the  lower  functions  with  a  remarkable 
degree  of  perfection.  Of  course  these  functions  are  under  constant  coordi- 
native  regulation  and  control  in  the  normal  animal,  but  experiments  and  ob- 
servation have  shown  how  much  of  such  activity  really  is  a  primary  function 
of  the  cord.  Of  these  activities  the  following  may  be  especially  mentioned: 
Muscular  tonus,  general  reflexes,  the  special  reflexes  of  micturition,  defecation, 
erection  and  the  sexual  reflex,  and  parturition,  some  of  which  will  be  briefly 
discussed. 

The  Center  oj  the  Tone  of  Muscles.  The  tonic  influence  of  the  spinal  cord 
on  the  sphincter  ani  and  sphincter  urethrae  will  be  presently  mentioned.  The 
cord  maintains  these  muscles  in  permanent  tonic  contraction.  The  condition 
of  the  sphincters,  however,  is  not  altogether  exceptional.  Their  contraction  is 
the  same  in  kind,  though  it  exceeds  in  degree,  that  condition  of  muscles  which 
has  been  called  tone,  a  condition  of  slight  contraction  which  they  always 
maintain  during  health.  This  tone  of  all  the  muscles  of  the  trunk  and  limbs 
depends  on  the  spinal  cord,  just  as  does  the  contraction  of  the  sphincters. 
If  an  animal  be  killed  by  injury  or  removal  of  the  brain,  the  muscles  retain 
their  tenseness,  but  if  the  spinal  cord  be  destroyed,  the  sphincter  ani  relaxes, 
and  all  the  muscles  become  loose,  flabby,  and  atonic,  remaining  so  till  rigor 
mortis  commences. 

If  an  animal,  such  as  the  dog,  be  held  off  the  ground  in  the  erect  position 
assumed  by  the  human  body,  when  the  trunk  and  hind  limb  muscles  are  not 
in  voluntary  contraction  the  limbs  will  assume  a  normal  pendular  position. 
In  the  pendular  position  the  legs  of  a  dog  with  cord  severed  hang  more  limp 
and  are  more  completely  extended.  The  muscles  of  the  former  exhibit  that 
tone  which  keeps  antagonistic  muscles  always  slightly  tense,  the  muscles  of  the 
latter  have  lost  the  tenseness. 

Whether  or  not  muscular  tone  is  maintained  through  the  constant  sub- 
minimal action  of  sensory  nerve  impulses  on  the  tonic  centers  of  the  cord,  or 
whether  these  centers  are  automatic  in  their  action,  is  a  question  that  can  be 
answered  only  by  inference.  The  probability  is  that  tone  is  a  reflex  activity, 
though  it  may  be  contributed  to  by  the  normal  healthy  nutritional  condition 
of  the  muscles  themselves — a  condition  which  is  itself  dependent  on  the 
trophic  influence  of  the  nerve  cells  of  the  cord  and  brain  stem. 


52(5  THE     NERVOUS     SYSTEM 

The  Ano-Spinal  or  Defecation  Center.  The  mode  of  action  of  the  ano- 
spinal  center  appears  to  be  this:  The  mucous  membrane  of  the  rectum  is 
stimulated  by  the  presence  of  feces  or  of  gas  in  the  large  bowel.  The  stim- 
ulus passes  up  by  the  afferent  nerves  of  the  hemorrhoidal  and  inferior  mesen- 
teric plexuses  to  the  center  situated  in  the  lumbar  enlargement  of  the  cord, 
and  is  reflected  through  the  pudendal  plexus  to  the  anal  sphincter,  and  to  the 
muscular  tissue  in  the  wall  of  the  lower  bowel.  In  this  way  there  is  produced 
a  relaxation  of  the  first  and  a  contraction  of  the  second,  and  expulsion 
of  the  contents  of  the  bowel  follows.  The  center  in  the  spinal  cord  is 
partially  under  the  control  of  the  will,  so  that  its  action  may  be  either 
inhibited  or  augmented.  The  action  may  be  helped  by  the  abdominal 
muscles,  which  are  voluntary  muscles,  but  are  also  stimulated  to  contract  by 
reflex  action. 

The  Vesicospinal  or  Micturition  Center.  The  vesico-spinal  center  acts 
in  a  very  similar  way  to  that  of  the  ano-spinal.  The  center  is  also  in  the 
lumbar  enlargement  of  the  cord.  It  is  stimulated  to  action  reflexly  by  the 
presence  of  urine  in  the  bladder.  The  action  may  be  voluntary  and  is  excited 
by  the  sensation  of  distention  of  the  bladder  by  the  urine.  The  sensory  fibers 
concerned  are  the  posterior  roots  of  the  lower  sacral  nerves.  The  action  of  the 
spinal  center  is  double,  or  it  may  be  supposed  that  the  center  consists  of  two 
parts,  one  of  which  is  usually  in  action  and  maintains  the  tone  of  the  sphincter, 
and  the  other  which  causes  contraction  of  the  bladder  and  other  muscles. 
When  evacuation  of  the  bladder  occurs  impulses  pass  to  that  part  of  the  center 
which  discharges  impulses  to  the  bladder  and  to  certain  accessory  muscles 
which  cause  their  contraction;  and  impulses  pass  to  that  part  of  the  center 
which  inhibits  the  tonic  action  on  the  sphincter  urethras  which  procures  its 
relaxation.  The  way  having  been  opened  by  the  relaxation  of  the  sphincter, 
the  urine  is  expelled  by  the  combined  action  of  the  bladder  and  accessory 
muscles.  The  cerebrum  may  exert  its  influence  on  the  reflex  not  only  by 
stimulating  the  center  to  action,  but  also  by  inhibiting  its  action. 

The  Genito-S pinal  Center.  The  presence  of  the  genito-spinal  center  is 
proven  by  the  fact  that  dogs,  and  even  man,  are  known  to  discharge  semen 
when  the  lumbar  cord  is  severed  and  all  voluntary  motion  and  sensibility  are 
lost.  The  center  situated  in  the  lumbar  enlargement  of  the  spinal  cord  is 
stimulated  to  action  by  sensory  impressions  from  the  glans  penis.  Efferent 
impulses  from  the  center  excite  the  successive  and  coordinate  contractions  of 
the  muscular  fibers  of  the  vasa  deferentia  and  vesiculae  seminales  and  of  the 
accelerator  urinae  and  other  muscles  of  the  urethra ;  and  a  forcible  expulsion 
of  semen  takes  place,  over  which  the  cerebral  centers  have  little  or  no  control, 
and  which,  in  cases  of  paraplegia,  are  not  felt. 

The  Erectai  Center.  This  center  is  also  situated  in  the  lumbar  region  and 
is  a  vascular  center,  already  described  in  the  chapter  on  Circulation.  It 
is  reflexly  excited  to  action  by  the  sensory  nerves  of  the  penis,  and  also  in  the 


CUTANEOUS    AND    MUSCLE   REFLEXES    AS    DIAGNOSTIC    SIGNS        527 

normal  animal  by  impulses  passing  down  from  the  cerebrum.  Efferent 
impulses  produce  dilatation  of  the  vessels  of  the  penis. 

The  Parturition  Center.  The  center  for  the  expulsion  of  the  contents  of 
the  uterus  in  parturition  is  situated  in  the  lumbar  spinal  cord  rather  higher 
up  than  the  other  centers  already  enumerated.  The  stimulation  of  the 
uterus  may,  under  certain  conditions,  excite  the  center  to  send  out  impulses 
which  produce  a  contraction  of  the  uterine  walls  and  expulsion  of  the  con- 
tents of  the  cavity.  The  center  is  independent  of  the  will  since  delivery 
takes  place  in  paraplegic  women,  and  also  while  a  patient  is  under  the  influ- 
ence of  chloroform.  Again,  as  in  the  cases  of  defecation  and  micturition,  the 
abdominal  and  thoracic  muscles  assist;  their  action  being  for  the  most  part 
reflex  and  involuntary. 

Inhibition  of  Reflex  Actions.  Movements  such  as  are  produced  by  stimu- 
lating the  skin  of  the  lower  extremities  in  the  human  subject,  after  division 
or  disorganization  of  a  part  of  the  spinal  cord,  do  not  always  occur  when  the 
cerebrum  is  active  and  the  connection  between  the  cord  and  the  brain  is  intact. 
The  reflex  which  would  occur  in  the  animal  with  spinal  cord  only  is  suppressed 
or  inhibited  in  the  normal  animal  through  the  regulative  action  of  the  higher 
cerebral  centers.  When  one  is  anxiously  thinking,  even  slight  stimuli  may 
produce  involuntary  and  reflex  movements.  So,  also,  during  sleep,  such  reflex 
movements  may  be  observed,  when  the  skin  is  touched  or  tickled;  for  example, 
when  one  touches  the  palm  of  the  hand  of  a  sleeping  child,  the  impression  on 
the  skin  of  the  palm  producing  a  reflex  movement  of  the  muscles  which 
close  the  hand.    But  when  the  individual  is  awake  no  such  reflex  is  produced. 

Further,  many  reflex  actions  are  capable  of  being  more  or  less  controlled 
or  even  altogether  prevented  by  the  will,  of  which  the  following  may  be  quoted 
as  familiar  examples: 

When  the  foot  is  tickled  we  can,  by  an  effort  of  will,  prevent  the  reflex 
action  of  jerking  it  away.  So,  too,  the  involuntary  closing  of  the  eyes  and 
starting  back,  when  a  blow  is  aimed  at  the  head,  can  be  similarly  restrained. 
Darwin  has  mentioned  an  interesting  example  of  the  way  in  which  such  an 
instinctive  reflex  act  may  override  the  strongest  effort  of  the  will.  He  placed 
his  face  close  against  the  glass  of  the  cobra's  cage  in  the  Reptile  House  at 
the  Zoological  Gardens,  and,  though  of  course  thoroughly  convinced  of  his 
perfect  security,  could  not  by  any  effort  of  the  will  prevent  himself  from 
starting  back  when  the  snake  struck  with  fury  at  the  glass. 

It  can  be  readily  shown,  by  comparing  a  spinal  frog  and  a  normal  unin- 
jured frog,  that  stimuli  which  call  forth  definite  reflexes  in  the  one  often  pro- 
duce no  movement  of  the  other. 

Cutaneous  and  Muscle  Reflexes  as  Diagnostic  Signs.  In  the  hu- 
man subject  two  classes  of  reflex  actions  dependent  upon  the  spinal  cord  are 
usually  distinguished,  the  alterations  of  which,  either  of  increase  or  of  diminu- 
tion, arc  indications  of  some  abnormality,  and  are  used  as  a  means  of  diag- 


528  THE     NERVOUS     SYSTEM 

nosis  in  nervous  and  other  disorders.  They  are  termed  respectively  cutaneous 
reflexes  and  muscle  reflexes.  Cutaneous  reflexes  are  set  up  by  a  gentle  stimu- 
lus applied  to  the  skin.  The  subjacent  muscle  or  muscles  contract  in  response. 
Although  these  cutaneous  reflex  actions  may  be  demonstrated  almost  any- 
where, yet  certain  of  such  actions  as  being  most  characteristic  are  distinguished, 
e.g.,  plantar  reflex;  gluteal  reflex,  i.e.,  a  contraction  of  the  gluteus  maximus 
when  the  skin  over  it  is  stimulated;  cremaster  reflex,  retraction  of  the  testicle 
when  the  skin  of  the  inside  of  the  thigh  is  stimulated,  and  the  like.  The 
ocular  reflexes,  too,  are  important.  They  are  contraction  of  the  iris  on  ex- 
posure to  light,  and  its  dilatation  on  stimulating  the  skin  of  the  cervical  region. 
All  of  these  cutaneous  reflexes  are  true  reflex  actions.  They  differ  in  different 
individuals,  and  are  more  esaily  elicited  in  the  young. 

Muscle  reflexes  or  tendon  reflexes  consist  of  a  contraction  of  a  muscle 
under  conditions  of  more  or  less  tension,  when  its  tendon  is  sharply  tapped. 
The  so-called  patellar-tendon  reflex  is  the  best  known  of  this  variety  of  re- 
flexes. If  one  knee  be  slightly  flexed,  as  by  crossing  it  over  the  other,  so  that 
the  quadriceps  femoris  is  extended  to  a  moderate  degree,  and  the  patella  tendon 
be  tapped  with  the  fingers,  the  muscle  contracts  and  the  foot  is  jerked  forward. 
Another  variety  of  the  same  phenomenon  is  seen  if  the  foot  is  flexed  so 
as  to  stretch  the  calf  muscles,  and  the  tendo  Achillis  is  tapped;  the  foot  is  ex- 
tended by  the  contraction  of  the  stretched  muscles.  It  appears,  however, 
that  the  tendon  reflexes  are  not  exactly  what  their  name  implies.  The  in- 
terval between  the  tap  and  the  contraction  is  said  to  be  too  short  for  the  pro- 
duction of  a  true  reflex  action.  It  is  suggested  that  the  contraction  is  caused 
by  local  stimulation  of  the  muscle,  but  that  this  would  not  occur  unless  the 
muscle  had  previously  been  stimulated  by  the  tension  applied,  and  placed  in 
a  condition  of  excessive  irritability.  It  is  probable  that  the  condition  on  which 
it  depends  is  a  reflex  change  in  the  spinal  irritability  acting  on  the  muscle  or 
exaggerated  muscular  tone,  which  is  admitted  to  be  a  reflex  phenomenon 
in  the  spinal  cord. 

Conduction  in  the  Spinal  Cord.  With  the  differentiation  of  the 
central  nerve  axis  in  vertebrates  the  conduction  in  the  spinal  cord  becomes 
of  increasing  importance,  reaching  its  maximum  in  man.  It  is  evident  that 
the  cord  is  the  path  by  which  all  nerve  impulses  arising  in  the  trunk  or  in  the 
arms  and  legs  must  reach  the  brain,  or  vice  versa.  Impulses  of  peripheral 
origin  can  and  do  produce  reflexes,  but  they  can  arouse  sensations  and  be  per- 
ceived only  after  they  have  been  conducted  to  the  cerebral  cortex.  Motor  im- 
pulses arising  in  the  brain  can  reach  the  anterior-horn  cells  of  the  cord  only 
through  the  cord  as  a  conducting  path.  The  continuity  of  the  cord,  therefore, 
while  not  necessary  for  the  execution  of  reflexes,  is  absolutely  necessary  for 
the  higher  coordinations  of  the  reflexes  and  for  the  excitation  and  controlling 
influence  of  the  brain. 

Illustrations  of  this  are  furnished  by  various  examples  of  paralysis,  but 


SENSORY    IMPULSES 


529 


by  none  better  than  by  the  common  paraplegia,  or  loss  of  sensation  and  volun- 
tary motion  in  the  lower  part  of  the  bod}-,  in  consequence  of  destructive 
disease  or  injury  of  a  section  including  the  whole  thickness  of  the  spinal  cord. 
Such  lesions  destroy  the  communication  between  the  brain  and  all  parts  of  the 
spinal  cord  below  the  seat  of  injury,  and  consequently  cut  off  from  their 
connection  with  the  brain  the  various  organs  supplied  with  nerves  issuing 
from  those  parts  of  the  cord. 

It  is  not  probable  that  the  conduction  of  motor  or  sensory  impulses  is 
effected,  under  ordinary  circumstances,  to  any  great  extent,  as  was  formerly 
supposed,  through  the  gray  substance  of  the  cord, 
i.e.,  from  cell  to  cell  through  the  short  filaments 
lying  wholly  within  the  gray  substance.  But 
cells  with  fibers  running  for  short  distances  in 
the  ground  bundles  are  numerous,  and  these 
short  connectives  are  capable  of  conducting  im- 
pulses along  the  cord.  All  parts  of  the  cord 
are  not  alike  able  to  conduct  all  impressions; 
and  as  there  are  separate  nerve  fibers  for  motor 
and  for  sensory  impressions,  so  in  the  cord  sepa- 
rate and  determinate  tracts  serve  to  conduct 
always  the  same  kind  of  impressions.  The  sen- 
sations of  touch,  and  perhaps  of  temperature  and 
pain,  do  not  appear  to  have  such  sharply  limited 
tracts  as  do  the  motor  impulses. 

Experimental  and  other  observations  point 
to  the  following  conclusions  regarding  the  con- 
duction of  sensory  and  motor  impressions  through 
the  spinal  cord.  Many  of  these  conclusions  must, 
however,  be  received  with  considerable  reserve. 

Sensory  Impulses.  The  sensory  impres- 
sions of  touch,  pain,  heat  and  cold,  and  of  the 
muscular  sense  are  conducted  to  the  spinal  cord 
by  the  posterior  nerve  roots.  Certain  sensory 
impressions  are  then  carried  directly  into  the 
postero-median  column  on  the  same  side,  and 
thence  up  to  the  nucleus  of  this  column  in 
the  medulla.  It  is  mainly  the  impulses  of  the  muscle  sense  and  of  the 
sense  of  touch  that  take  this  course  through  the  cord,  though  the  sense  of 
touch  is  not  wholly  interrupted  upon  injury  to  the  posterior  columns.  In 
lower  animals  it  is  scarcely  interfered  with  at  all.  The  posterior  columns 
unquestionably  are  the  primary  muscle  sensory  paths.  Visceral  sensations 
are  carried  by  the  posterior  root  fibers  to  the  cells  of  the  column  of  Clarke 
in  the  posterior  horn,  figure  361.     From  there  the  impulses  pass  to  the  direct 


Fig.  369. — Diagram  to  Show 
the  Manner  in  Which  the  Fibers 
of  the  Posterior  Nerve  Roots 
Enter  and  Ascend  the  Posterior 
Columns  of  the  Cord.  (Edin- 
ger.) 


530  THE  NERVOUS    SYSTEM 

cerebellar  tract  on  the  same  side,  and  thence  up  through  the  medulla  to  the 
cerebellum,  figure  396.  The  impressions  of  pain,  and  of  heat  and  cold,  are 
conveyed  to  the  nerve  cells  in  the  posterior  cornua  of  the  same  side  in  part, 
and  in  part  to  the  nerve  cells  in  the  posterior  cornu  and  median  gray  matter 
of  the  opposite  side.  From  this  point,  the  impulses  are  taken  up  again  by 
intermediary  neurones  and  conveyed  through  the  anterior  and  lateral  columns 
of  the  cord  to  the  brain  in  the  ascending  tract  of  Gowers.  By  reason  of  the 
great  number  of  collaterals  and  the  interpolation  in  the  course  of  the  sensory 
impulse  of  many  intermediary  neurones,  it  has  been  difficult  to  make  out  very 
sharply  defined  tracts  in  the  spinal  cord  for  the  conduction  of  the  sensations 
of  temperature,  pain,  and  touch.  If  one  set  of  fibers  is  destroyed  by  disease, 
others  seem  able,  through  the  collaterals,  to  take  up  its  function.  We  can  say 
that  injury  to  the  lateral  columns  has  resulted  in  loss  of  the  sense  of  pain, 
heat  and  cold,  but  with  only  partial  disturbance  of  touch  sensations. 

It  is  probable,  also,  that  pain  and  temperature  sensations  cross  over  at  once 
to  a  considerable  extent  and  pass  up  in  the  opposite  side  of  the  cord  to  which 
they  enter.  Touch  and  the  muscle  sense  impressions,  especially  the  latter, 
pass  up  largely  upon  the  same  side  until  they  reach  the  medulla  or  cerebellum. 

Motor  Impulses.  Motor  impulses  are  conveyed  downward  from 
the  cerebral  cortex  of  the  brain  along  the  pyramidal  tracts,  viz.,  the  crossed  or 
lateral,  and  the  direct  or  anterior,  chiefly  the  former.  In  the  crossed  pyr- 
amidal tract  the  impressions  pass  down  chiefly  on  the  side  opposite  to  which 
they  originate,  having  crossed  over  in  the  decussation  in  the  medulla.  But 
some  motor  impulses  do  not  cross  in  the  medulla,  but  descend  in  the  direct 
pyramidal  tract  to  lower  levels  of  the  cord,  where  they  cross  in  the  anterior 
commissure.  The  motor  fibers  for  the  legs  partially  pass  downward  in  the 
lateral  columns  of  the  same  side  without  decussation.  This  is  also  probably 
the  case  with  the  bilateral  muscles,  i.e.,  muscles  of  the  two  sides  that  act 
together,  such  as  the  intercostal  muscles  and  other  muscles  of  the  trunk. 

It  is  quite  certain,  as  was  just  now  pointed  out,  that  the  fibers  of  the  anterior 
nerve  roots  are  more  numerous  than  the  fibers  proceeding  downward  from 
the  brain  in  the  pyramidal  tracts,  or  the  so-called  pyramidal  fibers.  This  is 
because  each  pyramidal  fiber  is  really  a  very  long  nerve  process  or  axone, 
and  is  supplied  in  its  course  with  a  large  number  of  collaterals,  which  go  off 
at  different  points,  and  thus  put  it  in  relation  with  different  groups  of  nerve 
cells  in  the  anterior  cornua  at  various  levels.  Each  nerve  fiber  of  the  pyrami- 
dal tract,  by  means  of  its  collaterals,  can  control  a  number  of  nerve  cells,  and 
can  thus  coordinate  the  action  of  impulses  sent  out  through  the  anterior  roots 
to  a  number  of  groups  of  muscles.  In  other  words,  the  gray  matter  of  the 
anterior  cornua  contains  an  apparatus  with  various  complicated  coordinating 
powers,  which  apparatus  is  under  the  regulative  control  of  the  neurones  whose 
cells  of  origin  are  in  the  cortex  of  the  brain.  This  is  the  same  apparatus  that 
is  also  reflexly  influenced  by  sensory  impressions  passing  to  the  cord. 


GENERAL  ARRANGEMENT  OF  PARTS  OF  THE  BRAIN       531 

Division  of  a  single  anterior  pyramid  of  the  medulla  at  a  point  just  above 
the  decussation  is  followed  by  paralysis  of  voluntary  motions  in  the  muscles  of 
the  opposite  side  in  all  parts  below.  Disease  or  division  of  any  part  of  the 
cerebro-spinal  axis  below  the  seat  of  decussation  of  the  pyramids  is  followed 
by  impairment  or  loss  of  voluntary  motion  on  the  same  side  of  the  body. 
The  paralysis  is  never  quite  complete,  and  the  opposite  side  usually  shows  some 
slight  impairment  of  function  of  the  muscle. 

When  one-half  of  the  spinal  cord  is  cut  through  in  monkevs,  the  results 
are  as  follows  (Mott) :  Motor  paralysis  of  the  muscles  of  the  same  side  (never 
complete  paralysis  of  the  muscles  used  in  bilateral  associated  action),  followed 
by  gradual  recovery  of  muscular  movement,  except  of  the  finer  movements 
of  the  hand  and  foot;  wasting  and  flabbiness  of  the  muscles;  sensory  paralysis 
of  the  same  side  (temperature,  touch,  pain,  and  pressure) ;  temporary  vaso- 
motor paralysis  on  the  same  side.  The  temperature  of  the  affected  side  is 
depressed  i  to  30  F. 

III.    THE  BRAIN  STEM. 

General  Arrangement  of  Parts  of  the  Brain.  The  great  relative 
and  absolute  size  of  the  cerebral  hemispheres  in  the  adult  man  and  in  mammals 
to  a  great  extent  masks  the  real  arrangement  of  the  several  parts  of  the  brain. 
An  examination  of  the  accompanying  diagram,  figures  370,  371,  reveals  that 
the  parts  of  the  brain  are  disposed  in  a  linear  series,  as  follows  (from  before 
backward):  Olfactory  lobes,  cerebral  hemispheres,  thalamencephalon  (optic 
thalami  and  third  ventricle),  the  mid-brain  (corpora  quadrigemina  and  crura 
cerebri),  medulla  oblongata  and  cerebellum. 

This  linear  arrangement  of  parts  actually  occurs  in  an  early  stage  of  the 
development  of  the  human  fetus,  and  it  is  permanent  in  some  of  the  lower 
Vertebrata.  In  fishes  the  cerebral  hemispheres  are  represented  by  a  pair 
of  ganglia  intervening  between  the  olfactory  and  the  optic  lobes,  and  con- 
siderably smaller  than  the  latter,  their  adult  development  is  fairly  well  repre- 
sented by  the  figure  387.  In  Amphibia  the  cerebral  lobes  are  further  devel- 
oped, and  are  larger  than  any  of  the  other  ganglia. 

In  reptiles  and  birds  the  cerebral  ganglia  attain  a  still  further  development, 
and  in  Mammalia  the  cerebral  hemispheres  exceed  in  weight  all  the  rest  of  the 
brain.  As  we  ascend  the  scale,  the  relative  size  of  the  cerebrum  increases,  till 
in  the  higher  apes  and  man  the  hemispheres,  which  commenced  as  two  little 
lateral  buds  from  the  anterior  cerebral  vesicle,  have  grown  upward  and  back- 
ward, completely  covering  in  and  hiding  from  view  practically  all  the  rest  of  the 
brain.  At  the  same  time  the  smooth  surface  of  the  cerebral  cortex  of  many 
lower  mammalia,  such  as  the  rabbit,  is  replaced  by  the  labyrinth  of  convo- 
lutions of  the  human  brain. 

When  the  cerebral  hemispheres  are  removed,  several  large  basal  masses  of 


532 


THE     \KKVol S     SYSTEM 


nerve  substance  are  revealed:  the  optic  thalami,  the  corpora  quadrigemina, 
and  the  cms  cerebri.  These  structures,  together  with  the  pons  and  the  medulla, 
form  a  direct  continuation  forward  of  the  spinal  cord  and  sometimes  are  desig- 
nated under  the  general  term  of  the  brain  .si cm. 

For  convenience  of  description,  the  physiology  of  the  brain  will  be  presented 
by  discussing  the  three  main  subdivisions:  the  brain  stem,  the  cerebral  hemi- 
spheres, and  the  cerebellum. 

The  human  brain  on  superficial  examination  does  not  seem  to  follow  the 
general  plan  outlined  above,   but  when  the  cerebral  hemispheres  and  the 


Fig.  370. — Diagrammatic  Horizontal  Section  of  the  Vertebrate  Brain.  The  figures  serve  both 
for  this  and  the  next  diagram.  Mb,  mid-brain;  what  lies  in  front  of  this  is  the  fore-,  and  what 
lies  behind  the  hind-brain;  Lt,  lamina  terminalis;  Olf,  olfactory  lobes;  Hmp,  hemispheres; 
Th.  E,  thalamencephalon;  Pn,  pineal  gland;  Py,  pituitary  body;  F.M.,  foramen  of  Munro;  cs, 
corpus  striatum;  Th,  optic  thalamus;  CC,  crura  cerebri;  the  mass  lying  above  the  canal  rep- 
resents the  corpora  quadrigemina;  Cb,  cerebellum;  1-IX,  the  nine  pairs  of  cranial  nerves;  1, 
olfactory  ventricle;  2,  lateral  ventricle;  3,  third  ventricle;  4,  fourth  ventricle;  +,  iter  a  tertio 
ad  quartum   ventriculum.      (Huxley.) 


cerebellum  are  removed  then  it  is  found  that  what  remains  closely  follows 
the  plan  presented.  This  central  axis,  or  brain  stem,  is  shown  in  part  in 
figure  377. 

The  morphological  parts  of  the  brain  usually  given  are: 

1.  The  j ore-brain,  which  consists  of  the  corpora  striata  and  the  cerebral 
hemispheres. 

2.  The  inner-brain,  which  consists  of  the  optic  thalami  and  the  parts  en- 
closing the  greater  part  of  the  third  ventricle. 


GENERAL  ARRANGEMENT  OF  PARTS  OF  THE  HRAIX 


533 


3.  The  mid-brain,  which  comprises  th.2  crura  cerebri  and  the  corpora 
quadrigemina  enclosing  the  aqueduct  of  Sylvius. 

4.  The  hind-brain,  which  comprises  the  pons  Varolii,  forming  the  floor 
of  the  fourth  ventricle,  and  the  cerebellum,  forming  the  roof. 

5.  The  ajter-b  ain,  the  medulla  c  blongata  or  bulb. 


Fig.   371. — Longitudinal   and  Vertical  Diagrammatic  Section  of  a  Vertebrate  Brain.      Letters 
as  before.     Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pn  and  Py.      (Huxley.) 


Fig.  372. — Base  of  the  Brain,  r,  Superior  longitudinal  fissure;  2,  2' ,  2",  anterior  cerebral 
lobe;  3,  fissure  of  Sylvius,  between  anterior  and  4.  4'.  4".  middle  cerebral  lobe;  5,  5',  posterior 
lobe;  6.  medulla  oblongata.  The  figure  is  in  the  right  anterior  pyramid;  7,  8,  9,  10,  the  cerebellum; 
+1  the  inferior  vermiform  process.  The  figures  from  /.  to  IX,  are  placed  against  the  corresponding 
cerebral  nerves:  ///.  is  placed  on  the  right  crus  cerebri.  VI.  and  VII.  on  the  pons  Varolii;  X., 
the  first  cervical  or  suboccipital  nerve.      (Allen  Thomson.)       X  i. 


534 


THE     NERVOUS    SYSTEM 


THE  MEDULLA  OBLONGATA  OR  BULB. 

Anatomical  Structure.  The  medulla  oblongata  is  continuous  with 
the  spinal  cord  at  its  upper  end.  It  lies  within  the  cranial  cavity  and  forms 
the  first  part  of  the  brain  stem.  The  medulla  consists  of  masses  of  nerve 
cells  situated  in  the  interior,  but  pretty  generally  distributed  throughout 
the  mass.  The  cell-masses  are  subdivided  by  lamina?  of  nsrve  fibers  into 
groups,  or  nuclei,  which  give  origin  to  or  form  the  terminations  of  the  various 
ranks  of  nerve  fibers. 

The  nerve  fibers  are  arranged  partly  in  columns  and  partly  in  fasciculi 
traversing  the  central  cellular  matter.     The  medulla  oblongata  is  larger  than 


Fig.  373. — Plan  in  Outline  of  the  Brain  as  seen  from  the  Right  Side.  X  J.  The  parts  are  repre- 
sented as  separated  from  one  another  somewhat  more  than  natural,  so  as  to  show  their  connections. 
A,  Cerebrum;  /,  g,  h,  its  anterior,  middle,  and  posterior  lobes;  e,  fissure  of  Sylvius;  B,  cerebellum; 
C,  pons  Varolii;  D,  medulla  oblongata;  a,  peduncles  of  the  cerebrum;  b,  c,  d,  superior,  middle, 
and  inferior  peduncles  of  the  cerebellum.      ( From  Quain .) 

any  part  of  the  spinal  cord.  Its  columns  are  pyriform,  enlarging  as  they  pro- 
ceed toward  the  brain,  and  are  continuous  with  those  of  the  spinal  cord.  Each 
half  of  the  medulla,  therefore,  may  be  divided  into  three  columns  or  tracts  of 
fibers,  continuous  with  the  three  columns  of  which  each  half  of  the  spinal  cord 
is  made  up,  but  the  columns  are  more  prominent  than  those  of  the  spinal  cord, 
and  are  separated  from  each  other  by  deeper  grooves.  The  anterior,  contin- 
uous with  the  anterior  columns  of  the  cord,  are  called  the  pyramids.  The 
postero-median  and  postero-external  columns  are  also  represented  at  the 
posterior  or  dorsal  aspect  of  the  cord  as  the  fasciculus  gracilis  and  the  fasciculus 
cuneatus.  The  posterior  pyramids  of  the  medulla,  which  include  these  two 
columns  of  white  matter,  soon  become  much  increased  in  width  by  the  addi- 
tion of  a  new  column  of  white  matter  outside  the  other  two,  which  is  known 


ANATOMICAL    STRUCTURE 


535 


as  the  fasciculus  of  Rolando.  In  the  upper  portion  of  the  medulla  the  gracile, 
cuneati,  and  Rolandic  fasciculi  are  replaced  by  the  restiform  bodies  (the  in- 
ferior peduncles  of  the  cerebellum).  The  lateral  columns  of  the  cord  are 
scarcely  represented  as  such  in  the  bulb. 

It  may  be  said  then  that  the  bulb  at  its  commencement  differs  only  slightly 
in  size  from  the  cord,  with  which  it  is  continuous.  It  soon  becomes  larger 
both  laterally  and  antero-posteriorly.  It  opens  out  on  the  dorsal  surface  into 
a  space  which  is  known  as  the  fourth  ventricle,  and  from  being  a  cylinder  with  a 
central  canal  it  is  flattened  out  on  the  dorsal  surface  by  the  gradual  approach 
of  the  central  canal  to  that  surface,  where  it  is  directly  continuous  with  the 
fourth  ventricle. 

If  the  bulb  be  examined  on  its  anterior  or  ventral  surface,  it  is  found  that 
the  anterior  fissure,  which  is  a  continuation  of  the  same  fissure  in  the  cord,  is 


Fig.  374- 


Fig.  375. 


Fig.  3  74- — Ventral  or  Anterior  Surface  of  the  Pons  Varolii  and  Medulla  Oblongata,  a,  a,  An- 
terior pyramids;  b,  their  decussation;  c.  c,  olivary  bodies;  d,  d,  restiform  bodies;  e,  arciform 
fibers;  f,  fibers  passing  from  the  anterior  column  of  the  cord  to  the  cerebellum;  g,  anterior  col- 
umn of  the  spinal  cord;  h,  lateral  column;  p,  pons  Varolii;  i,  its  upper  fibers;  5,  5,  roots  of  the 
fifth  pair  of  nerves- 

Fig.  3  75- — Dorsal  or  Posterior  Surface  of  the  Pons  Varolii,  Corpora  Quadrigemina,  and  Me- 
dulla Oblongata.  The  peduncles  of  the  cerebellum  are  cut  short  at  the  side,  a,  a,  the  upper 
pair  of  corpora  quadrigemina;  b,  b.  the  lower;  ;",  /,  superior  penduncles  of  the  cerebellum;  c, 
eminence  connected  with  the  nucleus  of  the  hypoglossal  nerve;  e,  that  of  the  glosso-pharyngeal 
nerve;  i,  that  of  the  vagus  nerve;  d.d,  restiform  bodies;  p,  p,  posterior  pyramids;  v,  v,  groove  in 
the  middle  of  the  fourth  ventricle,  ending  below  in  the  calamus  scriptorius;  7,7,  roots  of  the  audi- 
tory nerves. 

occupied  at  the  most  posterior  part  by  fibers  which  are  crossing  from  one  side 
to  the  other.  This  is  what  is  known  as  the  decussation  of  the  pyramids.  It  is 
formed  of  the  fibers  which  occupy  the  postero-lateral  region  in  the  cord,  and 
are  called  the  crossed  pyramidal  fibers.  The  lateral  pyramidal  fibers  of  either 
side  after  crossing  the  middle  line  become  part  of  the  pyramid  of  the  opposite 
side;   the  rest  of  the  pyramid  is  made  up  of  the  fibers  which  in  the  anterior 


536 


THE     NERVOUS     SYSTEM 


column  of  the  cord  are  known  as  the  direct  or  uncrossed  pyramidal  tract. 
These  two  pyramidal  strands  of  fibers  are  those  which  degenerate  after  lesions 
of  the  parts  of  the  cerebrum  known  as  the  motor  areas  of  the  cortex.  They 
can  therefore  be  traced  downward  after  such  lesions  as  tracts  of  degeneration. 
They  are  the  descending  fibers  of  communication  between  the  cerebral  motor 
cells  of  the  cortex  and  the  different  segments  of  the  spinal  cord.  The  outer 
borders  of  the  anterior  pyramids  of  the  bulb  are  marked  by  the  exit  from  that 
part  of  the  nervous  axis  of  the  twelfth  or  hypoglossal  nerve.  Still  more  later- 
allvthan  this  nerve  there  is  on  either  side  a  rounded  elevation  or  column  which 


Optic  chiasma 

Optic  tract 

Corpus  geniculatum 
externum 

Corpus  genicu  latum 

internum 

Locus  perforatus 

posticus 


Middle  peduncle 
cf  the  cerebellum 


Restiform  body 

Olive 

Pyramid 

Anterior  superficial 

arcuate  fibres 

Decussation  of. 
pyramids 


IV?- 


— Optic  nerve 
-Infundibulum 
-Tuber  cinereum 
-Corpora  mammillaria 
-Oculo-motor  nerve  (III  ) 

Trochlear  nerve  (IV.) 
winding  round  the  crus 
cerebri 

Trigeminal  nerve  (V.) 

Abducent  nerve  (VI.) 
Facial  nerve  (VII.) 
Auditory  nerve  (VIII.) 

Vago-glossopharyngoal 
nerve  (IX.  and  X.) 

Hypoglossal 
nerve  (XII.) 

Spinal  accessory 
nerve  (XI.) 

First  cervical  nerve 


Fig.   376. — Front    View   of   the   Medulla,    Pons,   and   Mesencephalon  of  a  Full-Term   Human 

Fetus.      (Cunningham.) 


is  known  as  the  olivary  body.  It  begins  at  a  level  a  little  lower  than  the  open- 
ing of  the  fourth  ventricle.  On  the  dorsal  side  of  the  olivary  body  is  the  line 
of  origin  of  the  eleventh,  tenth,  and  ninth  nerves,  and  from  this  to  the  poste- 
rior fissure  is  the  posterior  pyramid. 

The  changes  in  structure  which  are  noticed  in  a  series  of  sections  of  the 
bulb  from  below  upward  may  be  summarized:  In  the  dorsal  or  posterior  re- 
gion, the  posterior  cornua  are  pushed  more  to  each  side  by  the  large  number 
of  sensory  fibers  ascending  in  the  posterior  columns,  and  terminating  in  the 
gracile  and  cuneate  nuclei.  The  substance  of  Rolando  is  increased  and  be- 
comes rounded,  reaching  almost  to  the  surface  of  the  bulb  on  each  side,  only  a 
small  tract  of  longitudinal  fibers  of  the  root  of  the  fifth  nerve  intervening. 


ANATOMICAL     STRUCTURE 


537 


538 


THE     NERVOUS     SYSTEM 


There  is  a  great  increase  of  the  reticular  formation  around  the  central  canal, 
and  the  lateral  approaches  the  anterior  cornu.  Then  at  the  ventral  or  anterior 
aspect  the  decussation  of  the  pyramids  begins.  By  this  crossing  over  of  the 
fibers,  the  tip  of  the  gray  anterior  cornu  is  cut  off  from  the  rest  of  the  gray  mat- 
ter. The  central  canal  is  pushed  farther  toward  the  posterior  surface,  first  of 
all  by  the  decussation  of  the  anterior  pyramids  just  mentioned,  and  later  on, 
i.e.,  above,  by  another  decussation  of  more  dorsal  fibers.  These  fibers  of 
the  second  decussation  as  they  cross  form  a  median  raphe  and  also  help  to 
break  up  the  remaining  gray  matter  into  what  is  called  a  reticular  formation. 


if>    &    v;9       f.c. 


Fig.  378. — Anterior  or  Dorsal  Section  of  the  Medulla  Oblongata  in  the  Region  of  the  Superior 
Pyramidal  Decussation,  a.nt.f..  Anterior  median  fissure;  f.a.,  superficial  arciform  fibers  emerg- 
ing from  the  fissure;  py,  pyramid;  n.ar.,  nuclei  of  arciform  fibers;  f.a.,  deep  arciform  becom- 
ing superficial;  o,  lower  end  of  olivary  nucleus;  n.L,  nucleus  lateralis;  f.r.,  formatio  reticularis; 
f.a.2,  arciform  fibers  proceeding  from  the  formatio  reticularis;  g.,  substantia  gelatinosa  of  Rolando; 
a.  V.,  ascending  root  of  fifth  nerve;  n.c. ,  nucleus  cuneatus;  n.c' ,  external  cuneate  nucleus;  n.g., 
nucleus  gracilis;  f.g.,  funiculus  gracilis;  p.m.f.,  posterior  median  fissure;  c  c,  central  canal  surround- 
ed by  gray  matter,  in  which  are  n.XI.,  nucleus  of  the  spinal  accessory,  and  n.XII.,  nucleus  of  the 
hypoglossal;    s.d.,  superior  pyramidal  decussation.      (Modified  from  Schwalbe.) 


These  fibers  arise  from  the  nuclei  of  the  fasciculus  gracilis  and  fasciculus 
cuneatus  of  either  side,  and  they  are  looked  upon  as  a  sensory  decussation. 

There  are  to  be  made  out  various  masses  of  cells  in  addition  to  the  reticu- 
lar formation,  viz.,  the  nuclei  of  the  fasciculus  gracilis  and  fasciculus  cuneatus, 
figure  379,  n.g.  and  n.c. 

The  olivary  bodies  extend  forward  almost  to  the  level  of  the  pons.  They 
consist  of  cells  and  fibers.  The  cellular  matter  consists  of  a  plicated  thinnish 
layer  of  small  nerve-cells,  folded  upon  itself  in  the  form  of  a  loop,  with  the  ends 
turned  inward  and  slightly  dorsal,  figure  379,  0.  The  gray  loop  is  filled  with 
and  covered  by  white  fibers. 

Internal  to  the  olivary  body  on  either  side  are  two  small  masses  of  gray 


TRACTS    THROUGH    THE    MEDULLA 


539 


matter,  one  more  ventral  to  the  other,  called  accessory  olives,  external  and 
internal,  and  on  the  surface  of  the  anterior  pyramid  on  either  side  a  small 
mass  of  gray  matter,  external  arcuate  nucleus;  laterally  another  mass  of  the 
same  material,  the  representative  of  the  lateral  nucleus  of  the  cord,  is  seen,  viz., 
the  antero-lateral  nucleus,  which  gives  origin  to  the  spinal  accessory  nerve. 

It  will  be  necessary  to  follow  as  shortly  as  possible  the  fibers  of  the  spinal 
cord  upward  into  the  bulb  and  beyond. 

Tracts  Through  the  Medulla.  The  crossed  and  direct  pyramidal  tracts 
have  already  been  described.  Nothing  definite  is  known  of  the  antero-lateral 
descending  tracts.     The  direct  cerebellar  tracts  pass  laterally  into  the  restiform 


TI.7JT.    n.X.     J\"  L  / 


Fir,.  379. — Section  of  the  Medulla  Oblongata  at  about  the  Middle  of  the  Olivary  Body,  f.l.a.. 
Anterior  median  fissure;  n.ar.,  nucleus  arciformis;  p.,  pyramid;  XII.,  bundle  of  hypoglossal 
nerve  emerging  from  the  surface;  at  b,  it  is  seen  coursing  between  the  pyramid  and  the  olivary 
nucleus,  o.;  f.a.e.,  external  arciform  fibers;  n.L,  nucleus  lateralis;  a.,  arciform  fibers  passing 
toward  restiform  body,  partly  through  the  substantia  gelatinosa,  g.,  partly  superficial  to  the 
ascending  root  of  the  fifth  nerve,  a.V .;  A".,  bundle  of  vagus  root  emerging;  f.r.,  formatio  retic- 
ularis; c.r.,  corpus  restiforme,  beginning  to  be  formed,  chiefly  by  arciform  fibers,  superficial  and 
deep;  n.c,  nucleus  cuneatus;  n.g.,  nucleus  gracilis;  t,  attachment  of  the  ligula;  j.s.,  funiculus 
solitarius;  n.X.,  n.X.',  two  parts  of  the  vagus  nucleus;  n.XIL,  hypoglossal  nucleus;  n.t.,  nucleus 
of  the  funiculus  teres;  n.am.,  nucleus  ambiguus;  r.,  raphe;  A.,  continuation  of  the  anterior  column 
of  cord;    o' ,  a",  accessory  olivary  nucleus;    p.c,  pedunculus  olivce.      (Modified  from  Schwalbe.) 


bodies  and  go  to  the  cerebellum.  The  antero-lateral  ascending  tracts  (Gow- 
ers)  appear  to  have  the  same  destination,  but  pass  indirectly  into  the  cere- 
bellum by  way  of  the  superior  medullary  velum;  some  of  the  fibers  probably 
pass  upward  to  higher  centers.  The  fibers  of  the  postero-median  and  postero- 
external columns  of  Goll  and  Burdach,  of  the  cord,  end  in  the  nuclei  of  the 
fasciculus  gracilis  and  cuneatus  respectively;  at  any  rate,  ascending  degenera- 
tion of  these  columns  cannot  be  traced  above  these  nuclei.  The  rest  of  the 
fibers  of  the  cord  appear  to  end  in  the  reticular  formation  of  the  bulb. 

Connections  of  the  Bulb  with  the  Cerebrum  and  Cerebellum.     The 


540  THE     NERVOUS    SYSTEM 

pyramidal  tracts  connect  the  bulb  with  the  cerebrum;  and  the  direct  cerebellar 
and  the  antero-laterai  ascending  tract,  tract  of  Gowers,  connect  it  with  the 
cerebellum.  Other  connections  of  the  bulb  with  the  cerebrum  and  with 
the  cerebellum  are: 

1.  Fibers  from  the  nucleus  gracilis  and  nucleus  cuneatus,  which,  as  we 
have  said,  are  the  endings  of  the  fibers  cf  the  columns  of  Gull  and  Burdach 
of  the  cord,  pass  in  sets  in  the  following  manner: 

a.  Internal  arcuate  fibers  pass  down  and  inward  to  the  opposite  side  in 
the  reticular  formation,  composing  in  part  the  superior  or  sensory  decussation, 
and  in  the  inter-olivary  region  enter  the  mesial  fillet,  which  passes  upward 
through  the  pons  to  end  about  the  cells  in  the  mid-brain  and  in  the  optic 
thalami.  These  fibers  are  probably  augmented  by  the  addition  of  fibers  from 
the  anterior  columns  of  the  cord,  and  by  fibers  arising  from  cells  in  the  sensory 
nuclei  of  the  cranial  nerves  ending  in  the  bulb. 

/).  External  arcuate  fibers,  after  decussating  in  the  same  way,  pass  outward 
superficially  over  the  anterior  pyramid  and  olivary  body,  reaching  the  resti- 
form  body  and  passing  to  the  side  of  the  cerebellum  opposite  to  their  nuclei  of 
origin.  These  fibers  appear  to  be  interrupted,  at  least  in  part,  in  the  external 
arcuate  nuclei.  They  connect  one  side  of  the  spinal  cord  with  the  opposite 
side  of  the  cerebellum  through  the  gracile  and  cuneate  nuclei. 

c.  Direct  lateral  fibers  pass  to  the  restiform  body  and  so  to  the  same  side 
of  the  cerebellum. 

2.  Fibers  from  the  olivary  body  pass  to  the  opposite  side  of  the  cerebellum 
through  the  reticular  formation  and  restiform  body. 

3.  Fibers  from  the  vestibular  nucleus  of  the  eighth  or  auditory  nerve  in 
the  floor  of  the  fourth  ventricle  pass  to  the  same  side  of  the  cerebellum. 

Functions  of  the  Medulla  Oblongata.  The  chief  functions  of  the 
medulla  are  those  of  carrying  impulses,  i.e.,  conduction,  between  the  cord  and 
brain;  of  carrying  on  activities  distinctly  reflex  in  character;  and  of  producing 
automatic  activity. 

The  Medulla  as  a  Conducting  Path.  The  medulla  is  the  pathway 
of  all  ascending  and  descending  nerve  impulses  between  the  spinal  cord  and 
most  of  the  peripheral  sensory  and  motor  apparatus  on  the  one  hand,  and  the 
cerebellum  and  the  cerebral  centers  on  the  other.  These  conducting  paths 
are  described  in  the  tracts  that  have  already  been  discussed  at  some  length. 
They  are  represented  graphically  in  the  diagrams,  figures  380  and  396. 

Reflex  Centers  of  the  Medulla.  The  larger  number  of  the  cranial 
nerves,  as  we  shall  presently  see,  take  their  origin  from  the  medulla  and 
pons.  Some  of  these  nerves  have  both  sensory  and  motor  roots,  while 
others  are  either  motor  or  sensory  exclusively.  A  large  percentage  of  the 
afferent  or  sensory  impulses  that  enter  the  medulla  produce  reflex  effects 
on  the  motor  nuclei  so  richly  represented  in  the  medulla.  The  nuclei,  or 
centers,  regulating  some  of  the  most  important  functions  of  the  body  are 


REFLEX     CENTERS     OF     THE     .MEDULLA 


541 


among  those  in  this  group.     When  certain  of  these  centers  are  interfered 
with,  death  follows. 

Life  may  continue  when  the  spinal  cord  is  cut  away  in  successive  portions 
from  below  upward  as  high  as  the  point  of  origin  of  the  phrenic  nerves.  In 
amphibia,  the  brain  has  been  all  removed  from  above,  and  the  cord  removed  as 
far  as  the  medulla  oblongata  from  below ;  yet  so  long  as  the  medulla  oblon- 


Fig.   380. — Diagram  of  Ascending  Conduction  Paths  from  the  Cord  through  the  Medulla  and 
the  Thalamus  to  the  Cerebral  Cortex.      (Cunningham.) 


gata  was  left  intact,  respiration  and  life  were  maintained.  But  if  the  medulla 
oblongata  is  wounded,  particularly  if  it  is  wounded  in  its  central  part  oppo- 
site the  origin  of  the  vagi,  the  respiratory  movements  cease,  and  the  animal 
dies  from  asphyxiation.  This  effect  ensues  even  when  all  parts  of  the  nervous 
system  except  the  medulla  oblongata  are  left  intact. 

Injury  and  disease  in  men  are  accompanied  by  the  same  nerve  disturbances 
as  are  exhibited  by  these  experiments  on  animals.  Numerous  instances  are 
recorded  in  which  injury  to  the  medulla  oblongata  has  produced  instantaneous 


542  .       THE     NERVOUS    SYSTEM 

death;  and,  indeed,  it  is  through  injury  to  it,  or  of  the  part  of  the  cord  con- 
necting it  with  the  origin  of  the  phrenic  nerve,  that  death  is  commonly  pro- 
duced in  fractures  attended  by  sudden  displacement  of  the  upper  cervical 
vertebrae. 

The  majority  of  the  medullary  centers  are  reflex  centers  simply,  and  are 
stimulated  by  afferent  or  by  voluntary  impulses.  Some  of  them  are  auto- 
matic centers  and  are  capable  of  sending  out  efferent  impulses  without  pre- 
vious stimulation  by  afferent  or  by  voluntary  impulses.  The  automatic 
centers  are,  however,  normally  influenced  by  reflex  or  by  voluntary  impulses. 

Some  of  these  reflex  centers  are:  i.  Bilateral  centers  for  the  movements  of 
deglutition.  The  medulla  oblongata  contains  in  the  motor  nuclei  of  the  ninth 
and  tenth  nerves  the  centers  whence  are  derived  the  motor  impulses  enabling 
the  muscles  of  the  palate,  pharynx,  and  esophagus  to  produce  the  successive 
coordinated  and  adapted  movements  necessary  to  the  act  of  deglutition,  page 
313.  This  is  proved  by  the  persistence  of  the  act  of  swallowing  in  some  of 
the  lower  animals  after  destruction  of  the  cerebral  hemispheres  and  cerebellum; 
its  existence  in  anencephalous  monsters;  and  by  the  complete  arrest  of  the 
power  of  swallowing  when  the  medulla  oblongata  is  injured  in  experiments. 

2.  Bilateral  centers  for  the  combined  muscular  movements  of  sucking,  the 
nerves  concerned  being  the  facial  for  the  lips  and  mouth,  the  hypoglossal  for 
the  tongue,  and  the  inferior  maxillary  division  of  the  fifth  for  the  muscles  of  the 
jaw. 

3.  Bilateral  centers  for  the  secretion  oj  saliva,  which  have  been  already 
mentioned,  page  305. 

4.  Bilateral  centers  for  vomiting,  page  330. 

5.  Bilateral  centers  for  coughing,  which  is  a  reflex  act  quite  independent 
of  the  respiratory  act.  The  coughing  center  is  situated  above  the  inspiratory 
part  of  the  respiratory  center. 

6.  Bilateral  centers  for  the  dilatation  oj  the  pupil,  the  fibers  from  which 
pass  out  through  the  spinal  cord  in  the  two  upper  dorsal  nerves  into  the  cervi- 
cal sympathetic. 

7.  The  respiratory  center  of  the  medulla  has  already  been  discussed  as 
regards  its  automatic  action.  It  is  only  necessary  to  repeat  here  that  although 
it  is  automatic  in  its  action,  being  capable  of  direct  discharge  of  respiratory 
impulses  with  no  other  stimulus  than  the  condition  of  the  blood  circulating 
within  it,  yet  it  is  constantly  reflexly  influenced  by  afferent  impulses.  The 
respiratory  center  has  been  proven  to  be  bilateral.  It  also  consists  of  an 
inspiratory  part  and  of  an  expiratory  part.  The  center  is  influenced  by 
voluntary  impulses,  but  one  can  not  voluntarily  control  this  center  to  the 
point  of  death.  The  vagus  influence  is  probably  the  most  constant  of  those 
stimulating  the  respiratory  center.  But  the  respiratory  reflexes  are  going  on 
constantly  in  response  to  afferent  impulses  flowing  into  the  medulla  from  nu- 
merous other  sensory  nerves  over  the  entire  body. 


THE     PONS     VAROLII  543 

8.  The  cardio-inhibitory  centers.  The  medulla  contains  the  centers  which 
maintain  the  proper  rhythm  of  the  heart,  these  centers  acting  through  the  vagus 
fibers.  These  terminate  in  a  local  intrinsic  mechanism  which  has  been  al- 
ready discussed.  It  is  claimed  that  the  center  can  be  stimulated  directly,  as 
by  the  condition  of  the  blood  circulating  within  it.  It  is  constantly  exerting 
a  tonic  influence  over  the  heart,  which  is  the  chief  reason  for  considering  it 
an  automatic  center.  But  the  cardio-inhibitory  center  is  primarily  a  re- 
flex center.  Sensory  or  afferent  impulses  arriving  over  the  sensory  paths  in 
the  vagus  itself,  by  abdominal  paths  through  the  sympathetic,  and  through 
cutaneous  nerves,  are  constantly  causing  reflex  discharges  of  inhibitory  impulses 
from  this  center. 

9.  Accelerator  centers  for  the  heart  are  present  in  the  medulla.  They 
are  reflexly  stimulated  by  sensory  impulses  arising  from  the  same  general  source 
as  in  the  preceding  center. 

10.  Vaso-motor  centers  which  control  the  unstriped  muscle  of  the  arteries, 
are  also  situated  in  the  medulla.  The  nerve  cells  constituting  the  center 
are  under  the  constant  influence  of  nerve  impulses  flowing  in  from  the  sensory 
and  motor  structures  throughout  the  whole  body.  The  reflexes  produced  by 
the  afferent  impulses  bring  about  the  variations  in  vaso-motor  tone  that  not 
only  regulate  the  general  vascular  responses  of  the  body,  but  control  and  co- 
ordinate the  local  changes  in  the  size  of  the  blood-vessels. 

1 1 .  Centers  for  the  secretion  of  sweat  exist  in  the  medulla.  The  medullary 
centers  control  the  subsidiary  spinal  sweat  centers.  They  may  be  excited  un- 
equally so  as  to  produce  unilateral  sweating. 

The  reflex  medullary  centers  described  above  are  comparable  to  the  spinal 
reflex  centers  previously  described.  If  the  medulla  were  completely  isolated 
from  the  higher  cerebral  centers,  and  the  spinal  cord  removed  with  the  ex- 
ception of  those  paths  which  are  necessary  to  maintain  respiration,  these  medul- 
lary reflex  centers  would  be  able  to  coordinate  afferent  impulses  in  the  same 
general  way  that  isolated  segments  of  the  cord  do.  In  the  living  body,  however, 
the  medullar}-  centers  are  under  the  influence  of  changes  going  on  in  regions 
of  the  nervous  system  both  above  and  below,  changes  which  constantly  in- 
fluence the  details  of  the  reactions.  The  activities  are  unconscious  reflexes 
in  the  same  sense  that  the  motor  reflexes  of  the  spinal  cord  are  unconscious 
and  machine-like.     The  main  difference  is  one  of  complexity  and  not  of  kind. 

The  Pons  Varolii.  The  pons  Varolii  is  generally  spoken  of  as  a 
great  commissure  of  fibers;  of  fibers  which  connect  with  the  two  halves  of 
the  cerebellum  and  which  connect  the  bulb  and  spinal  cord  with  the  upper 
part  of  the  brain.  It  must  not  be  forgotten  that  the  pons  contains  several 
smaller  collections  of  nerve  cells.  Sections  reveal  the  following  parts  or  struct- 
ures, beginning  from  the  anterior  or  ventral  surface. 

1.  Transverse  or  commissural  fibers  connect  one  side  of  the  cerebellum 
with  the  other  through  the  middle  peduncle.     These  fibers  connect  the  cere- 


544 


T 1 1  B     \  E  It  VO  US     SYSTEM 


bellar  cortex  with  the  cells  of  the  pontine  nuclei;  some  are  afferent,  some 
efferent;  some  end  in  the  gray  matter  of  the  pons  on  the  same  side  near  the 
ventral  surface;  others  cross  to  the  opposite  side  of  the  pons  and  then 
become  longitudinal,  passing  on  to  the  tegmentum. 

2.  Fibers  longitudinal  in  direction  are  arranged  in  larger  or  smaller  bundles 
and  are  separated  by  gray  matter.  Most  of  these  fibers  are  pyramidal  fibers 
which  pass  down  to  the  pyramids  of  the  medulla. 

3.  The  dorsal  portion  of  the  pons  is  made  up  to  a  considerable  extent  of  the 


.&*<*!>">„ 


Fig.  381. — Scheme  to  Show  the  Connections  of  the  Posterior  Longitudinal  Bundle, 
ningham,  modified  from  Held.) 


(Cun- 


reticular  formation  of  the  tegmental  region  together  with  one  or  two  distinct 
bundles  of  longitudinal  fibers.  The  chief  longitudinal  bundle,  situated  at  the 
junction  of  the  ventral  two-thirds  with  the  dorsal  third,  is  the  fillet,  including 
a  the  larger  mesial  fillet,  a  sensory  tract  previously  described  arising  in  the 
gracile  and  cuneate  nuclei,  and  by  the  lateral  fillet,  an  auditory  tract.  The 
second,  the  posterior  longitudinal  bundle,  is  situated  on  each  side  of  the  mid- 
line, just  internal  to  the  mesial  fillet. 

4.  In  the  upper  part  of  the  pons  a  mass  of  gray  matter  containing  pigment, 
the  locus  ceruleus,  forming  a  part  of  the  origin  of  the  fifth  nerve  and  in  the 
back  part  a  second  mass  of  gray  matter,  the  superior  olive. 


THE     MID -BRAIN 


545 


THE  MID-BRAIN. 

The  mid-brain  includes  the  crura  cerebri,  the  corpora  quadrigemina,  and 
the  geniculate  bodies. 

The  Crura  Cerebri.  The  crura  diverge  from  the  anterior  edge  of  the 
pons  Varolii  and  pass  upward  on  either  side  toward  the  cerebral  hemispheres. 
At  their  anterior  termination  each  of  them  appears  to  have  upon  its  dorsal 
surface,  to  the  inner  and  outer  sides  respectively,  two  large  masses  of  gray 
matter  which  have  been  already  spoken  of,  viz.,  the  optic  thalamus  and  the 
corpus  striatum.     The  crus  is  made  up  of  two  principal  parts.     The  crusta 


Fig.  382. — Diagram  of  the  Motor  Tract  as  Shown  in  a  Diagrammatic  Horizontal  Section  through 
the  Cerebral  Hemispheres,  Crura,  Pons,  and  Medulla.  Fr.,  Frontal  lobe;  Oc,  occipital  lobe; 
AF.,  ascending  frontal,  AP.,  ascending  parietal  convolutions;  PCF.,  pre-central  fissure,  in  front 
of  the  ascending  frontal  convolution;  FR.,  fissure  of  Rolando;  IPF.,  inter-parietal  fissure,  a  section 
of  crus  is  lettered  on  the  left  side;  5.V.,  substantia  nigra;  Py.,  pyramidal  motor  fiber  which  on 
the  right  is  shown  as  continuous  lines  converging  to  pass  through  the  posterior  limb  of  IC,  internal 
capsule  (the  knee  or  elbow  of  which  Is  shown  thus),  upward  into  the  hemisphere  and  downward 
through  the  pons  to  cross  the  medulla  in  the  anterior  pyramids.      (Gowers.) 


or  pes  is  in  the  ventral  position,  and  the  tegmentum  in  the  dorsal  position.    The 
two  are  separated  by  the  substantia  nigra. 

The  pes  consists  of  longitudinal  fibers  which  pass  anteriorly  between  the 
optic  thalamus  and  the  posterior  part  (lenticular  nucleus)  of  the  corpus  stria- 
tum, and  also  more  anteriorly.  In  this  situation  the  fibers  form  a  compact 
mass  which  spreads  out  dorsally  in  the  corona  radiata.  The  fibers  thus  have 
the  form  of  a  fan  bent  upon  itself  as  they  rise  to  pass  into  the  cerebral  hemi- 
sphere. This  constitutes  the  internal  capsule,  and  that  portion  of  it  which  forms 
the  angle  at  which  the  fibers  are  bent  is  called  the  genu  of  the  capsule.  The  fibers 
of  the  internal  capsule  are  connected  with  different  districts  of  the  cerebral 
cortex.  Briefly  the  connections  are,  a,  the  fronto-pontine  fibers  are  in  the 
35 


546'  THE    NERVOUS     SYSTEM 

anterior  limb  of  the  capsule;  b,  the  pyramidal  fibers  in  the  genu  and  the  anterior 
part  of  the  posterior  limb;  c,  the  temporo-pontine  fibers  in  the  posterior  part 
of  the  posterior  limb.  Fibers  connecting  the  optic  thalami  and  corpora 
striata  with  the  cerebral  cortex  run  in  the  capsule.  The  pes  and  the  corona 
radiata  form  the  great  sensory  and  motor  highway  to  and  from  the  cerebral 
cortex. 

The  tegmentum  is  the  continuation  anteriorly  of  the  reticular  formation  of 
the  medulla.  It  ends  for  the  most  part  in  the  neighborhood  of  the  optic  thala- 
mus and  in  the  parts  beneath.  The  tegmentum  of  either  side  is  supposed  to 
be  concerned  chiefly  with  afferent  impulses.  It  is  made  up  to  a  very  consid- 
erable extent  of  collections  of  gray  matter,  the  most  important  of  which  are 
the  substantia  nigra,  separating  the  pes  and  tegmentum,  and  the  nucleus  ruber, 
which  is  a  rounded  mass  situated  more  toward  the  aqueduct  of  Sylvius;  it 
serves  as  a  way-station  in  the  cerebello-cerebral  conduction  paths  and  also 
has  important  connections  with  the  spinal  cord.  The  locus  niger  extends 
back  as  far  as  the  posterior  corpus  quadrigeminum.  Posteriorly,  the  teg- 
mentum is  chiefly  reticular  in  structure. 

Corpora  Quadrigemina.  There  are  two  corpora  quadrigemina  on 
each  side,  the  anterior  and  posterior.  They  form  prominences  on  the  dorsal 
surface  of  the  mid-brain,  dorsal  to  the  aqueduct  of  Sylvius.  The  posterior 
corpora  quadrigemina  receive  through  the  lateral  fillet  fibers  from  the  coch- 
lear division  of  the  eighth  nerve.  They  are  closely  associated  with  the  median 
corpora  geniculata,  and,  like  these,  give  origin  to  fibers  which  continue  the 
auditory  conduction  path  upward  to  the  auditory  center.  The  anterior 
corpora  quadrigemina  receive  fibers  from  the  optic  nerve,  the  mesial  fillet, 
and  also  from  the  occipital  cortex,  as  will  be  more  fully  described  later.  They 
are  closely  associated  with  the  external  corpora  geniculata.  They  also  form 
reflex  centers  for  eye  muscles  in  the  ocular  adjustments. 

Corpora  Geniculata.  These  are  two  on  each  side  of  the  brain 
stem,  the  external  or  outer  and  the  median  or  inner.  The  external  corpus 
geniculatum  is  at  the  side  of  the  crus  and  appears  to  be  a  swelling  on  the  lateral 
division  of  the  optic  tract,  and  actually  receives  terminations  of  the  optic  fibers, 
thus  constituting  a  way-station  in  the  optic  conduction  paths.  Similarly 
the  median  appears  to  be  the  termination  of  the  median  division  of  the  optic 
tract,  from  which  it  receives  some  fibers,  figure  416,  but  it  is  more  intimately 
connected  with  the  auditory  tracts,  forming  a  way-station  between  the  lateral 
fillet  and  the  auditory  cortical  center,  figure  389. 

The  Optic  Thalami.  The  optic  thalami  are  oval  in  shape,  and  rest 
upon  the  crura  cerebri.  They  form  part  of  the  floor  of  the  lateral  ventricles  and 
their  inner  sides  bound  the  third  ventricle.  They  are  connected  by  a  trans- 
verse tract,  the  middle  commissure. 

Each  thalamus  has  several  collections  of  gray  matter,  forming  somewhat 
indistinctly  defined  masses  separated  by  white  fibers.     These  masses  of  gray 


THE     OPTIC     THALAMI  547 

matter  are  known  as  the  nuclei  oj  the  thalamus,  and  are  six  in  number.  They 
are  called  the  anterior  nucleus,  the  median  nucleus,  the  lateral  nucleus,  the 
ventral  nucleus,  the  pulvinar,  and  the  posterior  nucleus.  The  corpora  geni- 
culata  are  also  closely  associated  with  the  optic  thalamus.  The  anterior 
nucleus  is  composed  of  large  nerve  cells  which  receive  the  terminations  of 
axones  of  cells  of  the  corpora  mammillaria  at  the  base  of  the  brain  (bundle  of 
Vicq  d'Azyr).  There  they  meet  the  fibers  of  the  fornix,  which  establish 
a  relation  between  this  tubercle  of  the  thalamus  and  the  hippocampal  con- 
volutions. The  median  nucleus  is  connected  by  its  axones  with  the  cortex 
of  the  island  of  Reil  and  the  second  and  third  frontal  convolutions.  The 
lateral  nucleus  is  quite  large  and  lies  against  the  internal  capsule,  into  which  it 
sends  libers.  It  is  connected  with  the  central  convolutions.  The  ventral 
nucleus  lies  beneath  the  preceding;  it  is  relatively  small.  It  is  connected  with 
the  cortex  of  the  frontal  lobe  and  with  the  operculum,  the  central  convolutions, 
and  the  supramarginal  gyrus.  The  fifth  nucleus,  known  as  the  pulvinar,  forms 
the  posterior  tip  of  the  thalamus,  and  is  connected  with  the  optic  tract.  The 
posterior  nucleus,  lying  just  below  the  pulvinar,  is  a  small  mass  and  is  con- 
nected with  the  cortex  of  the  interior  parietal  convolution.  The  cells  of  the 
optic  thalamus  are  thus  seen  to  be  connected  with  a  large  area  of  the  cerebral 
cortex.  The  axones  spread  out  in  a  great  fan  in  the  corona  radiata,  the 
thalamus  sending  more  fibers  to  the  cortex  than  are  received  from  it. 

The  collections  of  nerve  cells  in  the  optic  thalamus  are  shown  by  anatomical 
investigations  and  by  methods  of  physiological  degeneration  to  be  on  the 
pathway  of  ascending  or  afferent  nerve  tracts.  Large  masses  of  sensory  fibers 
pass  through  the  optic  thalami,  the  majority  of  which  form  synapses  about  the 
nerve  cells  in  the  thalamus.  Even  in  those  cases  where  there  is  no  distinct 
ending  of  the  nerve  fiber,  collaterals  are  given  off  which  establish  physiological 
connection  with  the  nuclei. 

The  optic  thalamus  is  thus  closely  connected  with  large  areas  of  the  cortex. 
It  must  at  least  form  an  important  relay  in  all  those  activities  which  involve 
the  conscious  perception  of  sensory  stimuli  wherever  they  may  arise.  Flechsig 
even  claims  that  in  the  optic  thalamus  there  are  definite  points  of  sensory 
localization  corresponding  to  every  sensory  point  in  the  periphery  of  the  body 
(including  the  special  senses).  The  optic  thalamus  also  receives  fibers  from 
various  parts  of  the  cerebral  cortex,  thus  establishing  a  double  relation  with 
this  region. 

Owing  to  the  difficulty  of  those  operations  which  establish  isolation  of  the 
thalamus,  it  is  not  clear  to  what  extent  reflex  actions  may  take  place  through 
these  nuclei.  It  is  probable,  however,  that  extensive  coordinations  of  afferent 
impulses  may  be  mediated  by  the  nuclei  of  the  thalami.  Such  activities  as 
walking,  riding,  writing,  speaking,  etc.,  are  possibly  coordinated  reflexes 
through  the  optic  thalami,  perhaps  with  the  assistance  of  the  medulla  in  the 
case  of  walking. 


548  THE     NERVOUS     SYSTEM 

Corpora  Striata.  The  corpora  striata  are  situated  in  front  and  to 
the  outside  of  the  optic  thalami,  partly  within  and  partly  without  the  lateral 
ventricles. 

Each  corpus  striatum  consists  of  two  parts:  An  intraventricular  portion, 
the  caudate  nucleus,  which  is  conical  in  shape,  with  the  base  of  the  cone  for- 
ward (this  consists  chiefly  of  gray  matter),  and  an  extraventricular  portion,  the 
lenticular  nucleus,  separated  from  the  other  portion  by  the  internal  capsule. 
The  lenticular  nucleus  is  shown  in  a  horizontal  section  of  the  hemisphere  to 
consist  of  three  parts,  the  two  internal  called  globus  pallidas  major  and  minor, 
and  the  outer  called  the  pitta  men. 

The  cells  of  the  corpora  striata  are  somewhat  evenly  distributed,  and  not 
grouped  in  nuclei.  Their  axones  pass  for  the  most  part  into  the  internal 
capsule.  It  is  doubtful  if  these  ganglia  have  any  direct  anatomical  relations 
with  the  cortex  of  the  brain,  but  they  are  intimately  connected  by  fibers  to  and 
from  the  optic  thalami,  and  are  connected  with  the  substantia  nigra  (Flechsig). 
These  nuclei  are  developed  from  the  walls  of  the  embryonic  brain  tube  and 
are  probably  therefore  homologous  with  the  areas  of  the  cortex.  Their  lesion 
is  said  to  be  accompanied  by  disturbance  in  muscular  coordination.  Lesion 
of  the  left  lenticular  nucleus  is  said  to  cause  some  disturbance  in  the  power  of 
speech,  though  this  has  not  been  observed  in  the  case  of  the  right  nucleus. 
Lesions  of  the  corpora  striata  produce  disturbances  in  heat  regulation,  causing 
a  rise  of  body  temperature,  the  rise  amounting  to  as  much  as  20  or  30  C.  in 
the  rabbit.  The  rise  of  temperature  in  man  after  lesion  of  the  corpus  striatum 
on  one  side  is  said  to  be  chiefly  on  the  opposite  side  of  the  body  (Kaiser). 

THE  CRANIAL  NERVES. 

The  cranial  nerves  consist  of  twelve  pairs;  they  appear  to  arise  (superficial 
origin)  from  the  base  of  the  brain  in  a  double  series,  which  extends  from  the 
under  surface  of  the  anterior  part  of  the  cerebrum  to  the  lower  end  of  the 
medulla  oblongata.  Traced  into  the  substance  of  the  brain  and  medulla,  the 
roots  of  the  nerves  are  found  to  take  origin  from  various  masses  of  gray  matter. 

The  roots  of  the  first  or  olfactory  and  of  the  second  or  optic  nerves  will  be 
discussed  elsewhere.  The  third  and  fourth  nerves  arise  from  gray  matter 
beneath  the  corpora  quadrigemina ;  and  the  roots  of  origin  of  the  remainder  of 
the  cranial  nerves  can  be  traced  to  gray  matter  in  the  floor  of  the  fourth  ventri- 
cle, and  in  the  more  central  part  of  the  medulla,  around  its  central  canal,  as  low 
down  as  the  decussation  of  the  pyramids. 

According  to  their  several  functions  the  cranial  nerves  may  be  thus 
arranged : 

•xT  ,  •  ,  (  Olfactory',  Optic,  Auditory,     part    of    the    Glosso- 

JNervesofspecialsen.se <         ,  ,  ,  i   ,      ^  .         .      , 

(       pharyngeal,  and  part  or  the  I  ngeminal. 

Nerves  of  common  sensation. . .       The  greater  portion  of  the  Trigeminal. 


THE     THIRD     NERVE     OR     MOTOR       OCT"  LI 


549 


Nerves  of  motion. 


Mixed  nerves. 


S  The  Motor   Oculi;    Trochlearis,   lesser  division   of 
/       the  Trigeminal,  Abducens,  Facial,  and  Hypoglossal. 

\  Facial,    Glosso-pharyngeal,    Vagus,    and   Spinal  Ac- 
(       cessorv. 


The  physiology  of  the  first,  second,  and  eighth  nerves  will  be  considered 
with  the  Organs  of  Special  Sense. 

The  Third  Nerve  or  Motor  Oculi.  Origin.  The  third  nerve  arises 
in  three  distinct  bands  of  fibers  from  the  gray  nuclei  surrounding  the  aqueduct 
of  Sylvius  near  the  middle  line,  but  ventral  to  the  canal.  The  nucleus  of  origin 
consists  of  large  multipolar  ganglion  cells,  and  extends  to  the  back  part  of  the 
third  ventricle  as  far  as  the  level  of  the  superior  corpora  quadrigemina.     The 


Fig.  383. — Section  through  Anterior  Corpus  Quadrigeminum  and  Part  of  Optic  Thalamus,  s. 
Aqueduct  of  Sylvius,  gr,  gray  matter  of  the  aqueduct,  c.q.s,  quadrigeminal  eminence;  /,  stratum 
lemnisci;  o,  stratum  opticum,  c,  stratum  cinereum;  Th,  pulvinar  of  optic  thalamus:  c.g.e,  c.g.i, 
lateral  and  median  corpora  geniculata;  br.s,  br.t,  superior  and  inferior  brachia,  f,  fillet;  p.l, 
posterior  longitudinal  bundle;  r,  raphe;  III,  third  nerve,  and  n.lll,  its  nucleus;  I. p.p.  posterior 
perforated  space;  s.n,  substantia  nigra — above  this  is  the  tegmentum  with  the  circular  area  of  the 
red  nucleus;  cr,  crusta;  //,  optic  tract;  M,  medullary  center  of  hemisphere;  n.c,  nucleus  cau- 
datus;   st,  stria  terminalis.      (After  Quain,  from  Meynert.) 


fibers  pass  from  their  origin  partly  through  the  red  nucleus  to  their  superficial 
origin  in  front  of  the  pons  at  the  median  side  of  each  crus.  They  decussate  in 
the  middle  raphe. 

Function.  The  third  nerve  supplies  the  levator  palpebral  superioris  mus- 
cle, and  all  of  the  muscles  of  the  eyeball,  except  the  superior  oblique,  to 
which  the  fourth  nerve  is  appropriated,  and  the  rectus  externus,  which  receives 
the  sixth  nerve.  Through  the  medium  of  the  ophthalmic  or  lenticular  ganglion, 
of  which  it  forms  what  is  called  the  short  root,  it  also  supplies  motor  filaments 
to  the  iris  and  ciliary  muscle.  The  fibers  which  subserve  the  three  functions, 
accommodation,  contraction  of  the  pupil,  and  nerve-supply  to  the  external 
ocular  muscles,  arise  from  three  distinct  groups  of  cells.  Optic  reflexes  in- 
volving movements  of  the  eyeballs  are  through  fibers  from  cells  of  the  superior 
corpora  quadrigemina  (which  receive  fibers  from  the  optic  nerve).     These 


550 


THE     NERVOUS    SYSTEM 


fibers  from  the  corpora  quadrigemina  descend  (chiefly  through  the  posterior 
longitudinal  bundle)  to  the  nuclei  of  the  third,  fourth,  and  sixth  nerves,  thus 
rendering  possible  coordinated  reflex  movements  of  the  eye  muscles. 

When  the  third  nerve  is  stimulated  within  the  skull,  all  those  muscles  to 
which  it  is  distributed  are  convulsed.  When  it  is  paralyzed  or  divided,  the 
following  effects  ensue:  i,  The  upper  eyelid  can  be  no  longer  raised  by  the 
levator  palpebra?,  but  droops,  ptosis,  and  remains  gently  closed  over  the  eye, 
under  the  unbalanced  influence  of  the  orbicularis  palpebrarum,  which  is  sup- 


Fig.  384. — Fourth  Ventricle  with  the  Medulla  Oblongata  and  the  Corpora  Quadrigemina.  The 
roman  numbers  indicate  superficial  origins  of  the  cranial  nerves,  while  the  other  numbers  in- 
dicate their  deep  origins,  or  the  position  of  their  central  nuclei.  8,  8',  8",  Auditory  nuclei  nerves; 
/,  funiculus  teres;  A,  B,  corpora  quadrigemina;  eg,  corpus  geniculatum;  p.c,  pedunculus  cerebri; 
m.c.p,  middle  cerebellar  peduncle;  s.c.p,  superior  cerebellar  peduncle;  i.c.p,  inferior  cerebellar 
peduncle;  I.e.  locus  ceruleus;  e.t,  eminentia  teres;  a.c,  ala  cinerea;  a.n,  accessory  nuleus;  o, 
obex;    c,  clava;    f.c,  funiculus  cuneatus;   f.g,  funiculus  gracilis. 


plied  by  the  facial  nerve.  2,  The  eye  is  turned  outward  and  downward, 
external  strabismus,  by  the  unbalanced  action  of  the  rectus  externus  and  supe- 
rior oblique,  to  which  the  sixth  nerve  is  appropriated;  and  hence,  from  the 
irregularity  of  the  axes  of  the  eyes,  double  sight,  diplopia,  is  often  experienced 
when  a  single  object  is  within  view  of  both  the  eyes.  3,  The  eye  cannot  be 
moved  upward,  downward,  or  inward.  4,  The  pupil  becomes  dilated, 
mydriasis.     5,  The  eye  cannot  accommodate  for  short  distances. 

The    Fourth  Nerve,  or  Trochlearis.      Origin.     The    fourth    nerve 
arises  from  a  nucleus  consisting  of  large  multipolar  ganglion  cells  situated 


THE     FIFTH     NERVE,     OR    TRIGEMINAL 


551 


ventral  to  the  aqueduct  of  Sylvius,  and  the  inferior  corpus  quadrigeminum. 
The  fibers  from  both  sides  sweep  dorsally  around  the  central  gray  matter,  and 
reach  the  valve  of  Vieussens,  where  they  decussate  in  the  mid-line  of  the  roof, 
then  pass  forward  along  the  lateral  aspect  of  the  crus.  The  nucleus  of  the 
fourth  nerve  on  either  side  is  connected  with  those  of  the  third  and  sixth  nerves 
and  with  the  optic  reflex  center  previously  described. 

Functions.  The  fourth  nerve  is  exclusively  motor,  and  supplies  only  the 
trochlearis  or  superior  oblique  muscle  of  the  eyeball. 

The  Fifth  Nerve,  or  Trigeminal.  Origin.  The  fifth  or  trigeminal 
nerve  resembles  the  spinal  nerves  in  that  it  has  two  roots;  namely,  the  larger 


nyiri 


Fig.  385. — Section  Across  the  Pons,  About  the  Middle  of  the  Fourth  Ventricle,  py,  Pyramidal 
bundles;  po,  transverse  fibers  passing  pou  behind,  and  po.2.  in  front  of  py;  r.  raphe;  o.s,  su- 
perior olive;  a.V,  bundles  of  ascending  root  of  V.  nerve  enclosed  in  a  prolongation  of  the  sub- 
stance of  Rolando;  VI,  the  sixth  nerve;  nVl,  its  nucleus;  i'//,  facial  nerve;  VII. a,  intermediate 
portion,  nVH,  its  nucleus;  VIII,  auditory  nerve,  nVIII,  lateral  nucleus  of  the  auditory.  (After 
Quain.) 


or  sensory,  in  connection  with  which  is  the  Gasserian  ganglion,  and  the  small 
or  motor  root,  which  has  no  ganglion,  and  which  passes  under  the  ganglion  of  the 
sensory  root.  The  fibers  of  origin  of  the  fifth  nerve  come  from  the  floor  of  the 
fourth  ventricle.  The  motor  root  arises  to  the  inside  of  the  sensory,  about  the 
middle  of  each  lateral  half  of  the  fourth  ventricle.  The  sensory  fibers, 
however,  can  be  traced  down  in  the  medulla  oblongata  as  far  as  the  upper  part 
of  the  cord.  The  motor  nucleus  stretches  forward  as  far  as  the  superior  corpus 
quadrigeminum,  giving  rise  to  a  bundle  of  long  fibers  termed  the  descending 
root.  It  is  also  connected  with  the  locus  ceruleus.  The  sensory  nucleus 
receives  a  tract  of  sensory  fibers  from  the  trigeminus  extending  as  low  as  the 
second  cervical  nerve,  and  this  forms  a  tract  at  the  tip  of  the  posterior  cornu, 
between  it  and  the  restiform  body.     The  cells  of  origin  of  the  sensory  tract 


552 


THE     NERVOUS     SYSTEM 


are  in  the  Gasserian  ganglion.  The  nerve  appears  at  the  ventral  surface  of 
the  pons  near  its  front  edge,  at  some  distance  from  the  mid-line. 

Motor  Functions.  The  first  and  second  divisions  of  the  nerve,  which  arise 
wholly  from  the  larger  root,  are  purely  sensory.  The  third  division  is  joined 
by  the  motor  root  of  the  nerve  and  is  of  course  both  motor  and  sensory. 

Motor  branches  of  the  lesser  or  non-ganglionic  portion  of  the  fifth  supply 
the  muscles  of  mastication,  namely,  the  temporal,  masseter,  two  pterygoid, 
anterior  part  of  the  digastric,  and  mylohyoid.     FiLments  are  also  said  to  supply 


Fig.  386. — General  Plan  of  the  Branches  of  the  Fifth.  X  |.  I,  Lesser  root  of  the  fifth;  2,  greater 
root  passing  forward  into  the  Gasserian  ganglion;  3 ,  placed  on  the  bone  above  the  ophthalmic  nerve, 
which  is  seen  dividing  into  the  supra-orbital,  lachrymal,  and  nasal  branches,  the  latter  connected 
with  the  ophthalmic  ganglion;  4,  placed  on  the  bone  close  to  the  foramen  rotundum,  marks  the 
superior  maxillary  division,  which  is  connected  below  with  the  spheno-palatine  ganglion,  and 
passes  forward  to  the  infra-orbital  foramen;  5,  placed  on  the  bone  over  the  foramen  ovale,  marks 
the  inferior  maxillary  nerve,  giving  off  the  anterior  auricular  and  muscular  branches,  and  continued 
by  the  inferior  dental  to  the  lower  jaw,  and  by  the  gustatory  to  the  tongue;  a,  the  submaxillary 
gland,  the  submaxillary  ganglion  placed  above  it.  in  connection  with  the  gustatory  nerve;  6,  the 
chorda  tympani;    7,  the  facial  nerve  issuing  from  the  stylomastoid  foramen.      (Charles  Bell.) 


the  tensor  tympani  and  tensor  palati  (Kolliker).  The  motor  function  of  these 
branches  is  proved  by  the  violent  contraction  of  all  the  muscles  of  mastication 
in  experimental  irritation  of  the  third  or  inferior  maxillary  division  of  the  fifth 
nerve;  by  paralysis  of  the  same  muscles  when  the  nerve  is  divided  or  dis- 
organized; and  by  the  retention  of  the  power  of  these  muscles  when  the 
facial  nerve  is  paralyzed.  Whether  the  branch  of  the  fifth  nerve  which  is 
supplied  to  the  buccinator  muscle  is  entirely  sensory,  or  in  part  motor  also, 
must  remain  for  the  present  doubtful.     From  the  fact  that  this  muscle,  besides 


THE     FIFTH     NERVE,     OR    TRIGEMINAL  553 

its  other  functions,  acts  in  concert  or  harmony  with  the  muscles  of  mastication 
in  keeping  the  food  between  the  teeth,  it  might  be  supposed  from  analogy 
that  it  would  have  a  motor  branch  from  the  same  nerve  that  supplies  them. 
However,  the  so-called  buccal  branch  of  the  fifth  is,  in  the  main,  sensory. 

Sensory  Functions.  All  the  anterior  and  antero-lateral  parts  of  the  face 
and  head,  with  the  exception  of  the  skin  of  the  parotid  region,  acquire  com- 
mon sensibility  through  branches  of  the  ganglionic  division  of  the  fifth  nerve. 
The  muscles  of  the  face  and  lower  jaw  acquire  muscular  sensibility  through 
the  filaments  of  the  ganglionic  portion  of  the  fifth  nerve  distributed  to  them 
with  their  proper  motor  nerves. 

Through  its  ciliary  branches  and  the  branch  which  forms  the  long  root 
of  the  ciliary  or  ophthalmic  ganglion,  it  exercises  some  influence  on  the  move- 
ments of  the  iris.  When  the  trunk  of  the  ophthalmic  portion  is  divided,  the 
pupil  becomes,  according  to  Valentin,  contracted  in  men  and  rabbits,  and 
dilated  in  cats  and  dogs,  but  in  all  cases  becomes  immovable  even  under  all 
the  varieties  of  the  stimulus  of  light.  How  the  fifth  nerve  affects  the  iris  is 
unexplained;  it  has  been  suggested  the  influence  of  the  fifth  nerve  on  the  move- 
ments of  the  iris  may  be  ascribed  to  the  affection  of  vision  in  consequence  of 
the  disturbed  circulation  or  nutrition  in  the  retina. 

Trophic  Influence.  The  morbid  effects  which  division  of  the  fifth  nerve 
produces  in  'the  organs  of  special  sense  make  it  probable  that  the  fifth  nerve 
exercises  some  special  or  trophic  influence  on  the  nutrition  of  all  these  organs, 
although  the  effects  may  in  part  be  due  to  the  loss  of  sensibility  which  is  the 
natural  protective  safeguard.  Thus,  after  such  division  and  within  a  period 
varying  from  twenty-four  hours  to  a  week,  the  cornea  begins  to  be  opaque, 
and  later  it  grows  completely  white.  A  low  destructive  inflammatory  process 
ensues  in  the  conjunctiva,  sclerotic  coat,  and  in  the  interior  parts  of  the  eye. 
The  sense  of  smell  may  be  at  the  same  time  lost  or  gravely  impaired. 
Commonly,  whenever  the  fifth  nerve  is  paralyzed,  the  tongue  loses  the  sense 
of  taste  in  its  anterior  and  lateral  parts,  and  according  to  Gowers  in  the 
posterior  part  as  well. 

In  Relation  to  Taste.  The  tactile  sensibility  of  the  tongue  is  due  to  the 
lingual  branch  of  the  fifth  nerve,  which  supplies  the  anterior  and  lateral  parts 
of  the  tongue.  The  sense  of  taste  in  the  lateral  and  anterior  portions  of  the 
tongue  have  recently  been  traced  back  to  the  pars  intermedia  and  chorda 
tympani  of  the  seventh,  figures  387  and  388.  It  forms  also  one  chief  sensory 
link  in  the  nervous  circle  .or  reflex  action  in  the  secretion  of  saliva.  But,  de- 
ferring this  question  until  the  glosso-pharyngeal  nerve  is  to  be  considered, 
it  may  be  observed  that  in  some  brief  time  after  complete  paralysis  or  division 
of  the  fifth  nerve,  the  power  of  all  the  organs  of  the  special  senses  may  be  im- 
paired. They  may  lose  not  merely  their  sensibility  to  common  impressions, 
for  which  they  all  depend  directly  on  the  fifth  nerve,  but  also  their  sensibility 
to  the  special  stimuli  to  which  they  are  adapted. 


554 


THE     NERVOUS    SYSTEM 


The  Sixth  Nerve,  the  Abducens.  Origin.  The  sixth  nerve  arises 
from  a  compact  oval  nucleus,  situated  somewhat  deeply  at  the  back  part  of 
the  pons  near  the  middle  of  the  floor  of  the  fourth  ventricle.  The  eminentia 
teres  marks  its  position.  It  contains  moderately  large  nerve  cells  with  large 
axis-cylinder  processes.  It  is  connected,  figure  373,  with  the  nuclei  of  the  third, 
fourth,  and  seventh  nerves,  and  with  reflex  centers  of  the  optic  tracts,  as  pre- 
viously mentioned.     The  root  is  thin,  and  passes  ventrally  and  laterally  through 


Fig.  387. — The  Seventh  Nerve  and  Its  Branches.  VII,  Facial  nerve;  P.I,  pars  in- 
termedia; VIII,  auditory  nerve;  Aq.Fal,  aqueduct  of  Fallopius;  G.G,  geniculate  ganglion; 
E.S.P,  external  superficial  petrosal  nerve;  M.M,  middle  meningeal  artery;  G.S.P.,  great  super- 
ficial petrosal  nerve:  G. P. D,  great  deep  petrosal  nerve;  I.C,  internal  carotid  artery;  Vid,  Vidian 
nerve;  M.G.,  Meckel  s  ganglion;  Ty.Pl,  tympanic  plexus;  S.D.P,  small  deep  petrosal  nerve;  G.Pli, 
Glosso-pharyngeal  nerve  Ty,  tympanic  branch:  S.S.P.,  small  superficial  petrosal  nerve;  O.G, 
optic  ganglion:  Stap,  nerve  to  stapedius-  C.T,  chorda  tympani  nerve;  L,  lingual  nerve,  A.Va, 
communication  with  auricular  branch  of  vagus;  P. A,  posterior  auricular  nerve-  Sty.hy,  nerve  to 
stylo-hyoid;  Di,  nerve  to  digastric  (posterior  belly);  T.F,  temporal-facial  division;  C.F,  cervico- 
facial division;  T,  temporal  M,  malar;  I.O,  infra-orbital;  B,  buccal,  S.M,  supra-mandibular ; 
I.M,  infra-mandibular  branches.      (Cunningham.) 


the  reticular  formation,  to  the  surface,  which  it  reaches  at  the  lower  edge  of 
the  pons,  opposite  the  front  end  of  the  pyramid. 

Functions.  The  sixth  nerve  is  exclusively  motor,  and  supplies  only  the 
rectus  externus  muscle  of  the  eye.  The  muscle  is  paralyzed  when  the  nerve 
is  divided.  In  all  such  cases  of  paralysis  the  eye  squints  inward  and  cannot 
be  moved  outward. 

The  Seventh  Nerve,  or  Facial.  Origin.  The  facial  or  seventh  pair  of 
nerves  arises  from  the  floor  of  the  central  part  of  the  fourth  ventricle,  behind 
and  in  line  with  the  motor  nucleus  of  the  fifth,  to  the  outside  of  and  deeper 
•down  than  the  nucleus  of  the  sixth.  The  nucleus  is  narrower  in  front  than 
behind,  and  consists  of  large  motor  cells  with  well-marked  axis-cylinder  proc- 


THE     SEVENTH     NERVE,     OR     FACIAL  555 

esses,  which  are  gathered  up  at  the  dorsal  surface  of  the  nucleus  to  form  a  root. 
The  root  describes  a  loop  around  the  nucleus  of  the  sixth  nerve,  running  for- 
ward for  some  little  distance  dorsal  to  the  nucleus,  then  descending  vertically, 
passing  to  the  outside  of  its  own  nucleus,  between  it  and  the  descending  root 
of  the  fifth  nerve.  It  emerges  at  the  lower  margin  of  the  pons,  lateral  to  the 
sixth  nerve,  opposite  the  front  edge  of  the  groove  between  the  olivary  and 
restiform  bodies.  There  are  two  roots;  the  lower  and  smaller  is  called  the 
pars  intermedia,  and  the  upper,  pars  dura. 

Functions.  The  seventh  nerve  is  the  motor  nerve  of  all  the  muscles  of 
the  face,  including  the  platysma,  but  not  including  the  muscles  of  mastication, 
already  enumerated;  it  supplies,  also,  the  parotid  gland,  and,  through  the  con- 
nection of  its  trunk  with  the  Vidian  nerve,  some  of  the  muscles  of  the  soft  palate. 
It  supplies  the  stapedius,  the  lingualis  and  some  other  muscles  of  the  tongue, 


/ — /  brain        J 

pars     !n termed [~Wi<\  f n.  acust. 

>4Pv  r  auric,  vagi 


i  i 


'    gang,  geniz. 
petros.  sup  maj. 


■  motor  EZT. 


Fig.  388. — Dissection  of  the  Sensory  and  Motor  Divisions  of  the  Facial  in  a  20-cm.  Embryo 

(Pig).     (Streeter.) 

and  the  posterior  part  of  the  digastric  and  stylo-hyoid.  Its  branches  supply 
the  muscles  of  the  external  ear. 

Fibers  from  the  chorda  tympani  are  distributed  to  the  submaxillary  gland 
and  produce  secretion  when  stimulated. 

When  the  facial  nerve  is  divided  or  in  any  other  way  paralyzed,  the  loss  of 
function  in  the  muscles  which  it  supplies  interferes  with  the  perfect  exercise 
of  the  organs  of  the  special  senses.  Thus,  in  paralysis  of  the  facial  nerve  the 
orbicularis  palpebrarum  being  powerless,  the  eye  remains  open  through  the 
unbalanced  action  of  the  levator  palpebral.  The  conjunctiva  is  thus  contin- 
ually exposed  to  the  air  and  dust  and  is  liable  to  repeated  inflammation,  which 
may  end  in  thickening  and  opacity  of  the  cornea. 

The  sense  of  taste  may  be  weakened  or  wholly  lost  in  paralysis  of  the  facial 
nerve,  which  involves  the  chorda  tympani.  This  result,  which  has  been  ob- 
served in  many  instances  of  disease  of  the  facial  nerve  in  man,  appears  ex- 
plicable on  the  supposition  that  the  chorda  tympani  is  the  nerve  of  taste  to  the 
anterior  two-thirds  of  the  tongue,  its  fibers  being  distributed  with  the  so-called 


556  THE     NERVOUS    SYSTEM 

gustatory  or  lingual  branch  of  the  fifth.  Streeter  has  just  published  a 
study  of  the  development  of  the  seventh  and  eighth  nerves  in  which  he 
traces  the  chorda  tympani  through  the  pars  intermedia,  as  shown  in  figure 
388,  thus  settling  this  oft-disputed  question. 

The  Eighth  Nerve,  or  Auditory.  The  eighth  nerve  consists  of  two 
divisions,  anatomically  distinct  and  functionally  independent.  These  are  the 
vestibular  and  the  cochlear  divisions  of  the  auditory  nerve. 

The  cochlear  division  arises  in  the  spiral  ganglion  and  passes  to  the  medulla 
to  establish  immediate  connections  with  the  ventral  cochlear  nucleus  and  the 
tuberculum  acusticum.  The  central  relations  of  these  nuclei  are  established 
by  the  striae  acusticae,  the  trapezoideus,  and  the  lateral  fillet  with  the  internal 
corpus  geniculatum  and  the  inferior  corpus  quadrigeminum  of  the  opposite 
side,  as  told  by  figure  389.  These  latter  nuclei  send  tracts  to  the  auditory 
center  in  the  superior  temporal  gyrus. 

The  vestibular  division  arises  in  the  vestibular  ganglion,  which  is  entirely  dis- 
tinct from  the  cochlear  ganglion,  and  enters  the  medulla,  passing  to  the  lateral  or 
chief  auditory  nucleus.  From  this  point  the  relations  are  not  fully  established, 
but  apparently  fibers  pass  to  the  nucleus  fastigii  of  the  opposite  side  and  to  the 
vermis,  where  they  are  brought  into  relations  with  motor  descending  paths. 

Functions.  The  cochlear  branch  is  the  auditory  nerve  proper,  and  the 
vestibular  is  the  nerve  of  equilibrium. 

The  Ninth  Nerve,  or  Glosso-pharyngeal.  Origin.  The  glossophar- 
yngeal nerves,  figure  364,  IX,  arise  by  nuclei  intimately  associated  with 
those  of  the  vagus  and  spinal  accessory  nerves.  The  union  of  the  nuclei  is 
indeed  so  intimate  that  it  will  be  as  well  to  consider  the  origins  of  the  ninth, 
tenth,  and  eleventh  nerves  together. 

These  three  nerves  emerge  from  the  bulb  and  spinal  cord  in  their  numerical 
order  from  above  downward,  the  bulbar  portion  from  the  lateral  aspect  of 
the  bulb  in  a  line  between  the  olivary  and  restiform  bodies;  and  the  spinal 
portion  from  a  line  intermediate  between  the  anterior  and  posterior  nerve  roots 
as  far  down  as  the  sixth  or  seventh  cervical  spinal  nerves. 

The  combined  glosso-pharyngeal-accessory-vagus  nucleus  appears  to  con- 
sist of  two  parts,  viz.,  one  median  or  common  origin,  having  conspicuous 
nerve  cells  of  moderate  size,  and  three  lateral  origins,  having  but  few  cells  of 
small  size.  These  are:  1,  the  nucleus  ambiguus,  which  lies  on  the  lateral  side 
of  the  reticular  formation  and  is  the  motor  origin  of  the  glosso-pharyngeal, 
the  vagus,  and  the  spinal  accessory;  2,  the  fasciculus  solitarius,  situated  in 
the  bulb,  ventral  and  a  little  lateral  to  the  combined  nucleus,  is  also  called  the 
ascending  root  of  the  glosso-pharyngeal  nerve  or  the  respiratory  bundle;  and 
3,  the  spinal  portion,  which  takes  origin  from  a  group  of  cells  lying  in  the  ex- 
treme lateral  margin  of  the  anterior  cornu.  This  is  the  origin  of  the  spinal 
accessory;  it  corresponds  to  the  antero-lateral  nucleus  of  the  bulb,  and  the 
lateral  part  of  the  gray  matter  of  the  spinal  cord. 


THE     NINTH     NERVE,     OR    GLOSSOPHARYNGEAL 


557 


The  fibers  of  the  spinal  origin  of  the  nerve  pass  from  these  cells  through 
the  lateral  column  to  the  surface  of  the  cord.  The  fibers  from  the  median  part 
pass  in  a  ventral  and  lateral  direction  through  the  reticular  formation,  th^n 
ventral  to  or  through  the  gelatinous  substance  and  strand  of  fibers  connected 
with  the  fifth  nerve,  to  the  surface  of  the  bulb. 

The  fibers  from  the  nucleus  ambiguus  join  the  combined  nerve,  chiefly 
the  vagus  and  glosso-pharyngeal. 

The  bundles  of  fibers  of  the  fasciculus  solitarius  start  in  the  lateral  gray 


CORPORA  QUADRICEMINA 


Fig.  389. — The  Nuclei  of  Origin  and  Central  Connections  of  the  Auditory  and  Vestibular  Nerve. 

(Cunningham.; 


matter  of  the  cervical  cord  and  higher  in  the  reticular  formation  of  the  bulb, 
run  longitudinally  forward,  to  pass  into  the  roots  of  the  ninth  nerve.  It  is 
composed  of  sensory  fibers,  chiefly  of  the  glosso-pharyngeal. 

The  glosso-pharyngeal  nerve  gives  filaments  through  its  tympanic  branch 
(Jacobson's  nerve),  to  the  fenestra  ovalis  and  fenestra  rotunda,  and  the  Eu- 
stachian tube;   also  to  the  carotid  plexus,  and  through  the  petrosal  nerve,  to 


558  THE    NE'RVOUS     SYSTEM 

the  spheno-palatine  ganglion.  After  communicating  with  the  vagus  and, 
soon  after  it  leaves  the  cranium,  with  the  sympathetic,  with  the  digastric 
branch  of  the  facial,  and  the  accessory  nerve,  the  glosso-pharyngeal  divides 
into  the  two  principal  divisions  indicated  by  its  name,  which  supply  the  mucous 
membrane  of  the  posterior  and  lateral  walls  of  the  upper  part  of  the  pharynx, 
the  Eustachian  tube,  the  arches  of  the  palate,  the  tonsils  and  their  mucous 
membrane,  and  the  tongue  as  far  forward  as  the  foramen  cecum  in  the  middle 
line,  and  to  near  the  tip  at  the  sides  and  inferior  part. 

Functions.  The  glosso-pharyngeal  nerve  contains  some  motor  fibers, 
together  with  fibers  of  common  sensation  and  the  sense  of  taste. 

Motor  fibers  are  distributed  to  the  palato-pharyngeus,  the  stylo-pharyngeus, 
palato-glossus,  and  constrictors  of  the  pharynx. 

Sensory  fibers  of  touch  and  of  common  sensation  are  distributed  to  the 
pharynx,  the  tonsils,  and  posterior  palate.  Nerves  of  taste  are  supplied  to 
the  taste  buds  on  the  posterior  third  of  the  tongue  and  to  the  fauces. 

The  Tenth  Nerve,  Vagus  or  Pneumogastric  Nerve.  The  origin  of  the 
vagus  nerve  is,  as  we  have  just  seen,  situated  in  the  lower  half  of  the  floor  of 
the  fourth  ventricle,  figure  374.  Its  nucleus  is  said  to  represent  the  cells  of 
Clarke's  column  of  the  spinal  cord.  In  origin  it  is  closely  connected  with 
the  ninth,  eleventh,  and  the  twelfth.  The  combined  glosso-pharyngeal-vago- 
accessory  nuclei  lie  outside  of,  close  to,  and  parallel  with  the  nucleus  of  the 
twelfth.     There  are  two  main  vagal  nuclei:  one  motor,  the  other  sensory. 

Distribution.  It  has,  of  all  the  nerves,  the  most  varied  distribution  and 
functions,  either  through  its  own  filaments,  or  through  those  which,  derived 
from  other  nerves,  are  mingled  in  its  branches.  The  vagus  supplies  sensory 
branches,  which  accompany  the  sympathetic  on  the  middle  meningeal  artery, 
and  others  which  supply  the  back  part  of  the  meatus  and  the  adjoining  part 
of  the  external  ear.  It  is  connected  with  the  petrous  ganglion  of  the  glosso- 
pharyngeal, by  means  of  fibers  to  its  jugular  ganglion,  with  the  spinal  acces- 
sory, which  supplies  it  with  its  motor  fibers  for  the  larger  and  upper  portion 
of  the  esophagus,  and  with  its  inhibitory  fibers  for  the  heart;  also  with  the 
twelfth;  with  the  superior  cervical  ganglion  of  the  sympathetic;  and  with  the 
cervical  plexus.  The  parts  supplied  by  the  branches  of  the  vagus  are  as 
follows: 

1.  A  large  portion  of  the  mucous  membrane  and  probably  all  the  muscles 
of  the  pharynx  are  supplied  by  its  pharyngeal  branches. 

2.  The  mucous  membrane  of  the  under  surface  of  the  epiglottis,  and  of 
the  greater  part  of  the  larynx,  and  the  crico-thyroid  muscle,  by  the  superior 
laryngeal  nerve. 

3.  The  mucous  membrane  and  muscular  fibers  of  the  trachea,  the  lower 
part  of  the  pharynx  and  larynx,  and  all  the  muscles  of  the  larynx  except  the 
crico-thyroid  are  supplied  by  the  injerior  laryngeal  nerve.  It  also  supplies 
the  first  segment  of  the  esophagus. 


THE  TENTH  NERVE,  VAGUS  OR  PNEUMOGASTRIC  NERVE    559 


Fig.  390. 


Fig.  391. 


Fig.  390. — The  Distribution  of  the  Tenth  or  Vagus  Nerve.  Va.R,  Va.L.,  Right  and  left  vagi;  r, 
ganglion  of  the  root  and  connections  with  Sy.,  sympathetic,  superior  cervical  ganglion;  g.Ph.,  glosso- 
pharyngeal; Ace,  spinal  accessory  nerve;  m,  meningeal  branch;  A ur.,  auricular  branch;  t,  ganglion 
of  the  trunk  and  connections  with  Hy.,  hypoglossal  nerve;  Ci,  C2,  loop  between  the  first  two  cervi- 
cal nerves — Sy.,  sympathetic,  Ace.,  spinal  accessory  nerve;  Ph.,  pharyngeal  branch;  Ph. PL. 
pharyngeal  plexus;  S.L.,  superior  laryngeal  nerve;  I.L.,  internal  laryngeal  branch;  E.L..  external 
laryngeal  branch;  I.C.,  internal,  and  E.C.,  external  carotid  arteries;  Cai,  superior  cervical  cardiac 
branch;  Ca.2,  inferior  cervical  cardiac  branch;  R.L.,  recurrent  laryngeal  nerve;  Ca3,  cardiac 
branches  of  recurrent  laryngeal  nerve;  Ca4,  thoracic  cardiac  branch  (right  vagus);  A. P. PL,  an- 
terior, and  P. P. PL,  posterior  pulmonary  plexuses;  Oes.PL.  esophageal  plexus;  Gast.R.  and 
Gast. L.,  gastric  branches  of  vagus  (right  and  left);  Coe.PL,  celiac  plexus;  Hep. PL,  hepatic  plexus; 
PL,  splenic  plexus;    Ren. PL,  renal  plexus.      (Cunningham.) 

Fig.  391. — The  Constitution  of  the  Cardiac  Plexus.  Sy.,  Cervical  sympathetic  cord;  C.\. 
superior,  C.2,  middle,  and  C.3,  inferior  cervical  ganglia;  Car.i,  superior,  Car. 2,  middle,  and 
Car. 3,  inferior  cervical  cardiac  sympathetic  branches;  Va.,  vagus  nerve;  R.L.,  recurrent  laryngeal 
nerve;  s,  superior,  and  i,  inferior  cervical  cardiac  branches  of  vagus;  D.C.P.,  deep  cardiac  plexus; 
S.C.P.,  superficial  cardiac  plexus;  A. P. P.,  anterior  pulmonary  plexus;  P. P.P.,  posterior  pulmo- 
nary plexus;  R.Car.P.,  right,  and  L.Car.P.,  left  coronary  plexuses;  Art. Put.,  pulmonary  artery. 
(Cunningham.) 


560  THE     NERVOUS     SYSTEM 

4.  The  mucous  membrane  and  muscular  coats  of  the  esophagus  receive- 
fibers  from  the  esophageal  branches. 

5.  The  branches  of  the  vagus  form  the  supply  of  inhibitory  nerves  to  the 
heart  and  the  great  arteries. 

6.  The  lungs  are  supplied  through  the  anterior  and  posterior  pulmonary 
plexuses. 

7.  The  stomach,  the  intestines,  the  spleen,  and  the  liver  are  supplied  by 
the  gastric,  splenic,  and  hepatic  vagus  branches. 

Functions.  Throughout  its  whole  course  the  vagus  contains  both  sensory 
and  motor  fibers.  To  summarize  the  many  functions  of  this  nerve,  which 
have  been  for  the  most  part  considered  in  the  preceding  chapters,  it  may  be 
said  that  it  supplies,  1,  motor  fibers  to  the  pharynx  and  esophagus,  to  the 
stomach  and  intestines,  to  the  larynx,  trachea,  bronchi,  and  lungs;  2,  sensory 
and,  in  part,  3,  vaso-motor  fibers  to  the  same  regions;  4,  inhibitory  fibers 
to  the  heart;   5,  inhibitory  afferent  fibers  to  the  vaso-motor  center. 

Division  of  both  vagi  or  of  both  their  recurrent  branches  is  often  quickly 
fatal  in  young  animals;  but  in  old  animals  the  division  of  the  recurrent  nerve 
is  not  generally  fatal,  and  that  of  both  the  vagi,  even,  is  not  always  fatal. 

The  Eleventh  Nerve,  or  Spinal  Accessory.  This  nerve  arises  by  two 
nuclei,  one  the  nucleus  ambiguus  from  a  center  in  the  floor  of  the  fourth  ventri- 
cle, partly  but  chiefly  in  the  medulla  and  continuous  with  the  glosso-pharyn- 
geal-vagus  nucleus;  the  other,  from  the  outer  side  of  the  anterior  cornu  of  the 
spinal  cord  as  low  down  as  the  fifth  or  sixth  cervical  nerve.  The  fibers  from 
the  two  origins  come  together  at  the  jugular  foramen,  but  separate  again  into 
two  branches.  The  inner  arises  from  the  medulla  and  joins  the  vagus,  to 
which  it  supplies  fibers,  consisting  of  small  medullated  nerve  fibers.  The 
outer  consists  of  large  medullated  fibers  and  supplies  the  trapezius  and  sterno- 
mastoid  muscles.  The  muscles  of  the  larynx,  all  of  which  are  supplied,  ap- 
parently, by  branches  of  the  vagus,  are  said  to  derive  their  motor  nerves  from 
the  accessory;  and  Vrolik  makes  the  very  significant  statement  that  in  the 
chimpanzee  the  internal  branch  of  the  accessory  does  not  join  the  vagus  at 
all,  but  goes  direct  to  the  larynx. 

The  Twelfth  Nerve,  or  Hypoglossal.  Origin  and  Connections.  The 
nerve  arises  from  a  large-celled  and  very  long  nucleus  in  the  bulb,  extending 
from  the  floor  of  the  fourth  ventricle  to  the  level  of  the  olivary  bodies  close  to  the 
mid-line  and  inside  the  nucleus  ambiguus.  Fibers  from  this  nucleus  run  from 
the  ventral  surface  through  the  reticular  formation  in  a  series  of  bundles 
passing  between  the  olivary  nucleus  laterally  and  the  pyramid  and  accessory 
olive  medially,  to  gain  the  ventral  surface.  The  nerve  emerges  from  a  groove 
between  the  pyramid  and  olivary  body.  The  fibers  of  origin  are  continuous 
with  the  anterior  roots  of  the  spinal  nerves. 

This  nerve  is  the  motor  nerve  to  the  muscles  connected  with  the  hyoid  bone, 
including  those  of  the  tongue.     It  supplies  the  sterno-hyoid,  sterno-thyroid,  and 


THE     CEREBELLUM 


561 


omohyoid  through  its  descending  branch,  descendens  noni;  the  thyro-hyoid 
through  a  special  branch;  and  the  genio-hyoid,  stylo-glossus,  hyo-glossus, 
and  genio-hyo-glossus  and  linguales  through  its  lingual  branches. 

Functions.  The  function  of  the  hypoglossal  is  exclusively  motor.  In 
cases  of  hemiplegia  involving  the  functions  of  the  hypoglossal  nerve  the  tongue 
when  protruded  deviates  toward  the  paralyzed  side,  when  withdrawn  it  turns 
away  from  the  paralyzed  side.  Occasionally  it  is  not  possible  to  observe  any 
deviation  in  the  direction  of  the  protruded  tongue;  probably  because  the 
tongue  is  so  compact  and  firm  that  the  muscles  on  either  side  can  push  it 
straight  forward  or  turn  it  for  some  distance  toward  either  side.  In  hypo- 
glossal paralysis  from  cerebral  lesions  or  lesions  of  the  peduncles  the  paralysis 
is  contralateral. 

IV.  THE  CEREBELLUM. 

The  cerebellum  is  a  large  division  of  the  brain,  located  just  beneath  the 
cerebrum  and  behind  the  medulla  and  pons.     It  is  connected  with  the  rest 


Fig.  392. — Cerebellum  in  Section  and  Fourth  Ventricle,  with  the  Neighboring  Parts,  r, 
Median  groove  of  fourth  ventricle,  ending  below  in  the  calamus  scriptorius,  with  the  longitudinal 
eminences  formed  by  the  fasciculi  teretes,  one  on  each  side;  2,  the  same  groove,  at  the  place  where 
the  white  streaks  of  the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  the  ventricle;  3,  in- 
ferior cms  or  peduncle  of  the  cerebellum,  formed  by  the  restiform  body;  4,  posterior  pyramid; 
above  this  is  the  calamus  scriptorius;  5,  superior  crus  of  cerebellum,  or  processus  e  cerebello  ad 
cerebrum  (or  ad  testes);  6,  6,  fillet  to  the  side  of  the  crura  cerebri;  7,  7,  lateral  grooves  of  the  crura 
cerebri;    8,  corpora  quadrigemina.      (From  Sappey,  after  Hirschfeld  and  Leveille.) 


of  the  brain  by  three  peduncles  on  each  side:  the  superior,  the  middle,  and  the 
inferior  peduncle,  figure  392. 

The  cerebellum  is  composed  of  white  and  gray  matter,  the  latter  being 

external,  as  in  the  cerebrum,  and  like  it  infolded,  so  that  a  larger  area  may  be 

contained  in  a  given  space.     The  convolutions  of  the  gray  matter,  however, 

are  arranged  after  a  different  pattern,  as  shown  in  figure  393.     Besides  the 

36 


562 


THE     NERVOUS     SYSTEM 


gray  substance  on  the  surface,  there  is,  near  the  center  of  the  white  substance 
of  each  hemisphere,  a  small  capsule  of  gray  matter  called  the  corpus  dentatum, 
figure  393,  resembling  very  closely  the  corpus  dentatum  of  the  olivary  body  of 
the  medulla  oblongata. 

If  a  section  be  taken  through  the  gray  matter  of  the  cerebellum,  it  will  be 
found  to  be  composed  of  two  layers,  an  outer,  or  molecular,  and  an  inner,  or 
granular,  layer.  Each  of  these  layers  contains  a  large  number  of  peculiar- 
shaped  nerve  cells  and  very  rich  plexuses  of  nerve  fibers.  Recent  studies  of 
the  cortex  of  the  cerebellum  by  modern  methods  have  revealed  a  most  complex 
and  beautiful  arrangement  of  the  parts  of  the  cerebellum. 

The  General  Structure  of  the  Cerebellum.  The  molecular  layer 
of  the  cerebellum  contains  several  peculiar  types  of  nerve  cells,  of  which  may  be 


Fig.  393. — Outline  Sketch  of  a  Section  of  the  Cerebellum,  Showing  the  Corpus  Dentatum.  The 
section  has  been  carried  through  the  left  lateral  part  of  the  pons,  so  as  to  divide  the  superior  pe- 
duncle and  pass  nearly  through  the  middle  of  the  left  cerebellar  hemisphere.  The  olivary  body 
has  also  been  divided  longitudinally  so  as  to  expose  in  section  its  corpus  dentatum.  cr,  Crus  cerebri; 
f,  fillet;  q,  corpora  quadrigemina;  sp,  superior  peduncle  of  the  cerebellum,  divided;  mp,  middle 
peduncle  or  lateral  part  of  the  pons  Varolii,  with  fibers  passing  from  it  into  the  white  stem;  av, 
continuation  of  the  white  stem  radiating  toward  the  arbor  vita;  of  the  folia;  o,  olivary  body  with 
its  corpus  dentatum;    p,  anterior  pyramid.      (Allen  Thomson.)        • 


specially  mentioned  Purkinje's  cells  and  the  basket  cells.  The  cells  of  Pur- 
kinje  lie  along  the  internal  margin  of  the  layer,  being,  in  fact,  practically 
at  the  boundary  of  the  molecular  and  granular  layers.  They  measure  40  to  60  ,u 
in  diameter,  and  have  large,  round  nuclei.  Each  cell  gives  off  an  enormous 
number  of  branching  dendrites,  which  run  up  toward  the  surface  of  the  cere- 
bellum in  the  shape  of  a  bush. 

The  cells  of  Purkinje  give  off  at  their  deeper  surface  an  axone  which 
runs  down  into  the  white  matter  of  the  cerebellum. 

Lying  in  the  molecular  layer,  somewhat  external  to  the  Purkinje  cells, 
are  the  cells  of  the  type  known  as  basket  cells.  These  cells  have  a  number  of 
dendrites,  also  send  out  an  axone  which  runs  parallel  to  the  surface  of  the  cortex, 
which  gives  off  numerous  collaterals  in  its  course  that  form  baskets  around 
the  cell  bodies  of  the  Purkinje  cells,  figure  394,  ZK. 


THE     GENERAL     STKICTI  RE     OF     THE     CEREBELLUM 


563 


Fig.  394. — Transverse  Section  Through  a  Cerebellar  Folium  (after  Kolliker).  Treated  by  the 
Golgi  method.  P,  Axone  of  cell  of  Purkinje;  F,  moss  fibers;  K  and  K' ,  fibers  from  white  core  of 
folium  ending  in  molecular  layer  in  conection  with  the  dendrites  of  the  cells  of  Purkinje;  M, 
simple  cell  of  the  molecular  layer;  GR,  granule  cell;  GR1,  axones  of  granule  cells  in  molecular  layer 
cut  transversely;  M',  basket  cells;  ZK,  basket  work  around  the  cells  of  Purkinje;  GL,  neuroglia 
cell;   N,  axone  of  an  association  cell. 


Stellate 


molecular 
layer 


Fig.  395. — A,  Afferent  fiber  to  basket  (stellate)  cell;  B,  neuraxone  of  Purkinje  cell;  C,  afferent 
fiber  to  Purkinje  cell;    D,  afferent  (mossy)  fiber  to  granule  cell. 


5(!4  THE    NERVOUS    SYSTEM 

The  granular  layer  contains  a  large  number  of  very  small  granule-like 
cells  that  Golgi  was  the  first  to  show  are  really  nerve  cells.  They  are  only 
about  5  fi  in  diameter,  and  they  have  a  number  of  short  dendrites  which  end 
in  clubbed  extremities.  They  give  off  a  very  slender  axis-cylinder  process 
or  axone  which  runs  up  into  the  superficial  part  of  the  molecular  layer  and 
there  divides  in  a  T-shaped  fashion,  the  fibers  run  parallel  to  the  surface  of  the 
convolution  and  pass  in  between  the  branches  of  the  cells  of  Purkinje. 

The  white  substance  of  the  cerebellum  consists  of  nerve  fibers,  which  are  of 
three  kinds:  i,  Descending  fibers,  that  are  made  up  of  the  axis-cylinders 
of  the  cells  of  Purkinje,  carrying  impulses  down  from  the  cerebellar  cortex. 
2,  Ascending  fibers,  which  pass  into  the  granular  layer,  and  there  end  in  a 
number  of  very  short,  finely  divided  brushes  of  fibers  presenting  a  mossy  ap- 
pearance, so  that  these  are  known  as  the  mossy  fibers.  These  connect  with  the 
granular  cells  of  this  layer.  3,  Ascending  fibers,  which  pass  up  through  the 
granular  into  the  molecular  layer  and  there  break  up  into  a  fine  network  which 
interlaces  with  the  dendritic  branches  of  the  cells  of  Purkinje. 

Paths  through  the  Cerebellar  Cortex.  It  will  be  seen  that  the  ar- 
rangements for  the  transmission  and  diffusion  of  nerve  impulses  and  for  the  co- 
operation of  different  cells  are  extremely  complicated  and  delicate.  It  is  not 
possible  to  indicate  absolutely  by  any  schema  the  course  of  fibers  and  the 
course  of  impulses  through  the  cerebellum,  but  approximately  it  is  some- 
what like  that  in  the  accompanying  figure  396. 

Impulses  pass  up  along  the  ascending  fibers  to  the  granular  cells  by  way  of 
the  direct  cerebellar,  the  fibers  of  the  gracile  and  of  the  cuneatus,  from  the 
restiform  body,  etc.  These  cells,  being  stimulated,  send  the  impulses  by  their 
axis-cylinders  to  the  molecular  layer,  and  through  their  T-shaped  divisions  to 
the  dendrites  of  the  cells  of  Purkinje.  Thence  an  impulse  is  sent  out  by  the 
axis-cylinder  process  of  this  cell.  Other  ascending  impulses  are  brought  up 
by  those  fibers  which  pass  directly  to  the  molecular  layer  and  send  their  ter- 
minals winding  around  among  the  dendrites  of  the  cells  of  Purkinje.  Proba- 
bly impulses  pass  up  also  through  the  ascending  fibers  which  affect  the 
basket  cells,  and,  through  them  and  their  basket-like  terminals,  the  cells  of 
Purkinje.  Purkinje  cells  send  cerebellar  motor  fibers  to  the  nucleus  dentatus 
cerebelli  and  through  the  superior  peduncles  to  the  nuclei  of  the  oculo-motor 
nerves,  and  to  the  ventro-lateral  descending  tract  of  the  cord,  to  end  about 
the  anterior-horn  cells. 

Functions  of  the  Cerebellum.  With  the  exception  of  its  middle 
lobe,  the  cerebellum  is  itself  insensible  to  irritation  and  may  be  all  cut  away 
without  eliciting  signs  of  pain  (Longet).  Its  removal  or  disorganization  by 
disease  is  also  generally  unaccompanied  by  loss  or  disorder  of  sensibility; 
animals  from  which  it  is  removed  can  smell,  see,  hear,  and  feel  pain,  to  all 
appearances,  as  perfectly  as  before  (Flourens;  Magendie).  It  cannot,  there- 
fore, be  regarded  as  a  principal  organ  of  sensation.      Yet  if  any  of  its  crura 


FUNCTIONS     OF    THE     CEREBELLUM 


565 


be  touched,  pain  is  indicated;   and,  if  the  restiform  tracts  of  the  medulla  ob- 
longata be  stimulated,  the  most  acute  suffering  appears  to  be  produced. 

These  phenomena  may  properly  be  ascribed  to  the  activity  of  the  cerebral 
cortex,  since  the  number  of  collaterals  on  the  fibers  that  pass  to  cerebellar  tracts 
is  very  great,  and  impulses  arising  from  their  stimulation  may  reach  the  sen- 
sorium  by  paths  other  than  through  the  cerebellum. 


Cranial  Nerve 
(Vestibular) 


Fig.  396. — Scheme  of   Principal  Ascending  Cerebro- Spinal  (black)  and  Cerebellar  (red)  Con- 
duction Paths.      (Modified  from  Hardesty  in  Morris'  Anatomy.) 


The  experiments  of  Longet  and  many  others  agree  in  supporting  the  view 
that  no  stimulation  of  the  cerebellar  cortex  leads  to  localized  muscular  con- 
tractions. In  other  words,  there  is  no  localization  in  the  cerebellar  cortex 
as  in  the  cerebrum,  the  cerebellum  apparently  acting  as  a  whole.  If  the  cere- 
bellum be  removed,  as  was  done  by  Flourens  and  numerous  later  physiologists, 
a  very  profound  disturbance  in  motor  functions  occurs.     With  the  removal 


566  THE    nervous   system 

of  the  superficial  layers  of  the  cerebellum,  in  pigeons  particularly,  there  is 
increasing  feebleness  and  lack  of  harmony  of  the  muscles  concerned  in  lo- 
comotion. When  the  entire  organ  is  cut  away  in  pigeons  they  lose  the  power  of 
walking,  flying,  and  of  standing  in  the  usual  erect  way.  Their  power  of  pre- 
serving equilibrium  is  lost,  the  most  characteristic  feature.  Birds  do  not 
remain  in  a  state  of  stupor,  but  attempt  to  carry  out  the  usual  muscular  activi- 
ties. If  a  pigeon  is  laid  on  its  back  it  cannot  recover  its  erect  position,  though 
it  make  motions  to  do  so.  If  set  on  its  feet  it  will  fall  to  one  side  or  the  other, 
and  is  not  able  to  hold  its  head  in  the  customary  position.  The  endeavors  of 
the  animal  to  maintain  its  balance  are  insecure  and  uncertain,  resembling 
the  lack  of  muscular  control  of  a  drunken  man. 

Such  an  animal  does  not  lose  the  powTer  of  perceiving  sensations,  nor  of 
making  voluntary  efforts,  as  it  will  endeavor  to  avoid  the  blow  that  is 
threatened. 

The  experiments  afford  the  same  results  when  repeated  on  all  classes  of 
animals;  and  from  them  and  the  others  before  referred  to,  Flourens  inferred 
that  the  cerebellum  belongs  neither  to  the  sensory  nor  the  intellectual  ap- 
paratus; and  that  it  is  not  the  source  of  voluntary  movements,  although  it  be- 
longs to  the  motor  apparatus,  but  is  the  organ  for  the  coordination  of  the 
voluntary  movements,  or  for  the  excitement  of  the  combined  action  of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  diseases  of  this  organ 
confirms  the  view  taken  by  Flourens;  and,  on  the  whole,  it  gains  support  from 
comparative  anatomy — animals  whose  natural  movements  require  most 
frequent  and  exact  combinations  of  muscular  contractions  being  those  whose 
cerebella  are  most  developed  in  proportion  to  the  spinal  cord. 

We  must  remember,  too,  that  the  cerebellum  is  connected  with  the  posterior 
columns  of  the  cord  through  the  cuneate  and  gracile  nuclei  as  well  as  with  the 
direct  cerebellar  tract,  all  of  which  probably  convey  to  the  middle  lobe  muscular 
sensations.  It  is  also  connected  with  the  auditory  nerves  and  bulb  by  the  in- 
ternal and  external  arcuate  fibers;  and  with  the  tegmentum  through  the  red 
nuclei.  Its  connection  with  the  efferent  tracts  from  the  different  cerebral 
lobes  through  the  pons  is  also  highly  important.  Movements  of  the  eyes  also 
occur  on  direct  stimulation  of  the  middle  lobe.  It  seems,  therefore,  to  be 
connected  in  some  way  with  all  of  the  chief  sensory  impulses  which  have  to  do 
with  the  maintenance  of  the  equilibrium,  and  is  generally  included  in  the  ner- 
vous apparatus  which  is  supposed  to  govern  this  function  of  our  bodies. 

Foville  supposed  that  the  cerebellum  is  the  organ  of  muscular  sense,  i.e.,  the  organ 
by  which  the  mind  acquires  that  knowledge  of  the  actual  state  and  position  of  the  muscles 
which  is  essential  to  the  exercise  of  the  will  upon  them;  and  it  must  be  admitted  that  all 
the  facts  just  referred  to  are  as  well  explained  on  this  hypothesis  as  on  that  of  the  cerebellum 
being  the  organ  for  combining  movements.  A  harmonious  combination  of  muscular 
actions  must  depend  as  much  on  the  capability  of  appreciating  the  condition  of  the  muscles 
with  regard  to  their  tension,  and  to  the  force  with  which  they  are  contracting,  as  on  the 
power  which  any  special  nerve-center  may  possess  of  exciting  them  to  contraction.     And 


FORCED     MOVEMENTS  567 

it  is  because  the  power  of  such  harmonious  movement  would  be  equally  lost,  whether  the 
injury  to  the  cerebellum  involved  injury  to  the  seat  of  muscular  sense  or  to  the  center 
for  combining  muscular  actions,  that  experiments  on  the  subject  afford  no  proof  in  one 
direction  more  than  the  other. 

Forced  Movements.  The  influence  of  each  half  of  the  cerebellum 
is  directed  to  muscles  on  the  opposite  side  of  the  body;  and  it  would  appear 
that,  for  the  right  ordering  of  movements,  the  actions  of  its  two  halves  must  be 
always  mutually  balanced  and  adjusted.  For  if  one  of  its  crura,  or  if  the 
pons  on  either  side  of  the  middle  line,  be  divided,  so  as  to  cut  off  from  the 
medulla  oblongata  and  spinal  cord  the  influence  of  one  of  the  hemispheres 
of  the  cerebellum,  strangely  disordered  movements  ensue — forced  movements. 
The  animals  fall  down  on  the  side  opposite  to  that  on  which  the  crus  cerebelli 
has  been  divided,  and  then  roll  over  continuously  and  repeatedly ;  the  rotation 
being  always  round  the  long  axis  of  their  bodies,  and  generally  from  the  side 
on  which  the  injury  has  been  inflicted.  The  rotations  sometimes  take  place 
with  much  rapidity;  as  often,  according  to  Magendie,  as  sixty  times  in  a  min- 
ute, and  may  last  for  several  days.  Similar  movements  have  been  observed 
in  men;  as  by  Serres  in  a  man  in  whom  there  was  apoplectic  effusion  in  the 
right  crus  cerebelli;  and  by  Belhomme  in  a  woman  in  whom  an  exostosis 
pressed  on  the  left  crus.  They  may,  perhaps,  be  explained  by  assuming  that 
the  division  or  injury  of  the  crus  cerebelli  produces  paralysis  or  imperfect  and 
disorderly  movements  of  the  opposite  side  of  the  body;  the  animal  falls,  and 
then,  struggling  with  the  disordered  side  on  the  ground,  and  striving  to  rise 
with  the  other,  pushes  itself  over;  and  so  again  and  again,  with  the  same  act, 
rotates  itself.  Such  movements  cease  when  the  other  crus  cerebelli  is  divided ; 
but  probably  only  because  the  paralysis  of  the  body  is  thus  made  almost  com- 
plete. Other  varieties  of  forced  movements  have  been  observed,  especially 
those  named  "  circus  movement,"  when  the  animal  operated  upon  moves 
round  and  round  in  a  circle;  and  again  those  in  which  the  animal  turns  over 
and  over  in  a  series  of  somersaults.  Nearly  all  these  movements  may  result 
on  section  of  one  or  other  of  the  following  parts:  viz.,  crura  cerebri,  medulla, 
pons,  cerebellum,  corpora  quadrigemina,  corpora  striata,  optic  thalami,  and 
even,  it  is  said,  of  the  cerebral  hemispheres. 

V.    THE   CEREBRUM. 

That  portion  of  the  brain  which  is  concerned  with  all  intellectual  functions 
is  the  cerebrum  or,  more  strictly  speaking,  the  cerebral  cortex.  The  cerebral 
cortex  is  the  seat  of  those  activities  which  we  describe  as  intelligence — 
including  states  of  consciousness,  acts  of  idea  formation  and  volition,  and 
the  phenomenon  of  memory. 

The  cerebrum  includes  the  cerebral  cortex,  the  mass  of  fibers  connecting 
it  with  lower  portions  of  the  brain,  the  basal  nuclei  represented  by  the  corpora 


568 


THE     NERVOUS     SYSTEM 


striata,  optic  thalami,  etc.  The  structure  and  function  of  these  basal  nuclei 
have  already  been  given  briefly,  so  we  may  turn  our  attention  now  to  the  cere- 
bral cortex. 

Structure  of  the  Cerebral  Cortex.  The  cerebral  cortex  forms  a  large 
part  of  the  mass  of  the  cerebrum,  in  fact  of  the  whole  brain.  Its  superficial 
appearance  presents  a  series  of  ridges  and  folds,  the  gyri  and  sulci.  For  gen- 
eral convenience  anatomists  have  divided  the  cerebral  cortex  into  five  lobes: 
the  frontal,  that  portion  in  front  of  the  fissure  of  Rolando  extending  down  to  the 
Sylvian  fissure;  the  parietal,  extending  from  the  Sylvian  fissure  to  the  parieto- 
occipital fissure,  and  bounded  below  by  the  Sylvian  fissure;  the  temporal  lobe, 
just  ventral  to  the  parietal;  the  central  lobe,  or  island  of  Reil;  and  the  oc- 
cipital lobe,  which  includes  the  posterior  portion  of  the  cortex  behind  the 


ocap. 

tie  pass. 
sup. 


Fig.  397. — Left  Hemisphere,  from  Without.      (After  Eberstaller.) 


parieto-occipital  fissure.  And,  finally,  the  olfactory  and  limbic  lobes  together 
make  up  the  olfactory  division  of  the  brain.  For  the  detailed  arrangements  of 
the  cortex  the  reader  is  referred  to  text-books  of  anatomy. 

In  a  transverse  section  of  the  cerebral  cortex  there  is  shown  an  external 
gray  layer  chiefly  composed  of  nerve  cells  and  an  internal  white  portion  of 
nerve  fibers.  The  folding  of  the  cortex  into  convolutions  increases  the  total 
mass  of  gray  matter  enormously. 

The  gray  or  cellular  external  part  of  the  cerebral  cortex  has  an  average 
thickness  of  about  3  mm.;  being  thin  in  the  occipital  and  frontal  region,  2  mm., 
and  thick  in  the  precentral,  4  mm.,  and  postcentral  convolutions. 

Several  types  of  nerve  cells  have  been  described  as  present  in  the  cortex,  the 
exact  type  and  relative  proportion  varying  somewhat  in  different  regions. 
The  typical  characteristic  cell,  however,  is  the  pyramidal  cell.  The  pyramidal 
cell,  as  its  name  implies,  has  a  pear-shaped  cell  body  with  numerous  proto- 
plasmic processes.     The  apex  of  the  cell  is  directed  toward  the  surface  of  the 


STRUCTURE  OF  THE  CEREBRAL  CORTEX 


569 


cortex,  and  supports  numerous  branches  which  extend  out  into  the  adjacent 
territory,  bringing  it  into  contact  with  a  relatively  large  number  of  nerve  cells. 
These  processes  are  dendritic  in  character.  The  base  of  the  pyramidal  cell 
always  has  a  single  axis-cylinder  process  which  is  directed  down  into  the  white 
matter,  and  which  in  some  cases  ultimately  finds  its  course  through  the  corona 
radiata  into  the  pyramids  below.     The  axis-cylinder  processes  give  off  col- 


frontalp^^ 


°ccipUal-P°l- 

Fig.  398. — The  Cerebrum,  from  Above.      (After  Eberstaller.) 


Fig.  399. — Right  Hemisphere   from  Within.      (After  Eberstaller.) 


570 


THE     NERVOUS     SYSTEM 


laterals  both  in  the  immediate  neighborhood  of  the  cell  and  somewhat  deeper 
along  its  course. 

In  the  superficial  layer  of  the  cortex  there  is  a  peculiar  type  of  small  cell, 
first  described  by  Cajal.  Most  of  these  cells  are  fusiform  in  shape,  with  the 
long  axis  parallel  to  the  surface  of  the  convolution.  They  give  off  usually  two 
axones  which  run  along  parallel  to  the  surface  and   send  down  numerous 


Fig.  400. 


Fig. 


Fig.  400. — Typical  Pyramidal  Cell  from  the  Human  Cortex,  a,  Cell  body;  b,  main  dendrites 
with  gemmules;  c,  lateral  dendrites;  d,  axone  and  collaterals.  Only  a  small  part  of  the  axone 
is  shown.      (Bailey.) 

Fig.   401. — Showing  the  Stages  in  the  Development  of  a  Pyramidal  Cell.      (Ram6n  y  Cajal.) 

fine  collaterals  at  right  angles.  Another  form  of  Cajal  cell,  triangular  or 
quadrangular  in  shape,  is  also  seen.  Both  forms  have,  as  a  rule,  more  than 
one  axone.  Their  collaterals  pass  in  a  horizontal  direction,  forming  a 
fine  band  of  fibers,  known  as  tangential  fibers.  A  third  type  of  cell  is  the 
fusiform  or  polymorphous.  Some  of  these  are  strictly  fusiform  in  shape  and 
lie  with  their  axes  parallel  to  the  surface  of  the  convolution.  They  give  off 
protoplasmic  processes  which  pass  down  toward  the  white  matter,  some  of 
them  turning  to  run  in  a  horizontal  direction.  The  fusiform  and  polymorphous 
cells  are  grouped  in  the  same  layer. 


STRUCTURE  OF  THE  CEREBRAL  CORTEX 


571 


Besides  these  cells  we  find  scattered  through  the  cortex  a  considerable 
number  of  the  neuroglia  cells.  The  character  and  position  of  these  are  shown 
in  figure  402. 

The  general  arrangement  of  the  layers  of  the  cortex  is  described  very  dif- 
ferently by  the  various  authors.    It  is  not  uniform  in  the  different  parts  of  the 


Fig.  402. — The  Principal  Constituent  Elements  of  the  Gray  Cortical  Layer  of  the  Anterior 
Cerebrum.      (After  Ram6n  y  Cajal.) 

brain.  The  simplest  and  most  representative  type,  however,  of  the  arrangement 
is  that  in  which  the  cortex  is  divided  into  four  layers.  The  outermost,  or  super- 
ficial, known  as  the  molecular  layer,  contains  relatively  few  cells.  It  is  com- 
posed of  neuroglia  tissue,  embedded  in  which  are  a  number  of  cells  of  the 
Cajal  types,  which  have  just  been  described.  There  are  also  in  this  layer 
many  neuroglia  cells.     In  the  superficial  part  of  the  layer  of  some  areas  of  the 


572 


THE     NERVOUS     SYSTEM 


cortex  are  many  tangential  fibers.  The  second  layer  is  composed  of  small 
pyramidal  cells.  In  parts  of  the  brain  there  are  here  interposed  what  are 
known  as  the  vertical  fusiform  cells.  The  third  layer  is  composed  of  large 
pyramidal  cells,  in  which,  however,  one  also  sees  many  small  pyramidal  cells. 
The  fourth  layer  is  composed  of  the  fusiform  and  polymorphous  cells,  beneath 
which  is  the  white  substance.  This  arrangement  is  shown  in  the  accompanying 
figures,  404  and  405.  The  gray  matter  of  the  brain  contains,  however,  not 
only  these  layers  and  cells,  but  an  infinitely  rich  mass  of  fibers,  which  can  be 
shown  to  have  a  certain  definite  arrangement.  Some  of  the  fibers  are  vertical, 
passing  directly  up  to  the  most  superficial  layers  of  cells ;  others  have  a  hori- 
zontal   direction,  dividing    the  gray  matter    into    different    layers.     These 


Fig.  403. — Scheme  of  Descending  Conduction  Pathways  from  the  Cerebrum  to  Lower  Nerve 

Centers. 


layers  of  fibers  have  received  different  names.  A  typical  arrangement  is 
shown  in  figure  405.  The  most  conspicuous  fibers  are  those  of  certain 
large  triangular  or  pyramidal  cells. 

The  efferent  or  axone  fibers  from  the  cerebral  cortex  may  be  divided  into 
three  classes:  1,  the  projection  fibers,  which  descend  .through  the  corona 
radiata  and  internal  capsule,  to  end  in  lower  centers;  2,  the  commissural 
fibers,  which  cross  to  the  opposite  cerebral  hemisphere,  chiefly  through  the 
corpus  callosum;  3,  the  association  fibers,  which  pass  in  bundles  beneath 
the  cortex,  to  end  in  other  regions  of  the  same  hemisphere. 

It  is  by  means  of  projection  fibers  and  collaterals  that  associations  are 
made  with  nerve  cells  in  the  optic  thalamus,  tegmentum,  and  pons,  and 
through  the  latter  region  with  tracts  going  to  the  cerebellum. 


STRUCTURE  OF  THE  CEREBRAL  CORTEX 


573 


ff-x 


'IV 


^ 


Pt* 


m 


I-  j 


■  ■>—  ■ 


..Tangential  fibers    (Vi 
d'Azyr's  ribbon) 


.  .Stria  of  Bechterew 


.  .Superradiary     network     (of 
the  second  and  third  layers) 


.  .Striae  of  Baillarger 


..Intermediary    network     (of 
the  third  and  fourth  layers) 


..Meynert's  intracortical  asso- 
ciation fibers 


..Subcortical    association 
fibers 


Fig.  404. 


Fig.  405. 


Fig.  404. — Schematic  Diagram  of  the  Different  Layers  of  the  Cerebral  Cortex.  (After  Ram6n 
y  Cajal.)  I,  II,  III,  and  IV,  Layers  of  cortical  cells.  M,  Molecular  layer;  pPy,  layer  of  small 
pyramidal  cells;    gPy,  layer  of  large  pyramidal  cells;    Pm,  layer  of  polymorphous  cells. 

Fig.  405. — Schematic  Diagram  Showing  the  Arrangement  ot  the  Nerve  Fibers  in  the  Cerebral 
Cortex.     The  dotted  lines  separate  the  four  cellular  layers  of  Cajal.     Sb,  White  substance. 


574 


THE     NERVOUS     SYSTEM 


Weight  of  the  Brain  and  Cord.  The  brain  of  an  adult  man  weighs  from  48  to  50 
oz.,  about  1,550  grams,  or  about  2  per  cent  of  the  body  weight.  It  exceeds  in  absolute 
weight  that  of  all  the  lower  animals  except  the  elephant  and  whale.  Its  weight,  relatively 
to  that  oj  the  body,  is  exceeded  only  by  that  of  a  few  small  birds,  and  some  of  the  smaller 
monkeys. 

In  the  new-born  child  the  brain  (weighing  10  to  14  oz.)  is  about  10  per  cent  of  the 
weight.  At  the  age  of  7  years  the  weight  of  the  brain  already  averages  40  oz.,  and  about 
14  years  the  brain  not  infrequently  reaches  the  weight  of  48  oz.  Beyond  the  age  of  forty 
years  the  weight  slowly  but  steadily  declines  at  the  rate  of  about  1  oz.  in  10  years. 

The  average  weight  of  the  female  brain  is  less  than  the  male;  and  this  difference  per- 
sists from  birth  throughout  life.  The  difference  amounts  to  about  5  oz.  Thus  the  average 
weight  of  an  adult  woman's  brain  is  about  44  oz. 

The  brains  of  idiots  are  generally  much  below  the  average,  some  weighing  less  than  16 
oz.     Still  the  facts  at  present  collected  do  not  warrant  more  than  a  very  general  statement, 


Fig.  406. — Brain  of  the  Orang,  §  Natural  Size,  Showing  the  Arrangement  of  the  Convolutions. 
Sy,  Fissure  of  Sylvius;  R,  fissure  of  Rolando;  EP,  external  perpendicular  fissure;  Olf,  olfactory- 
lobe;  Cb,  cerebellum;  PV,  pons  Varolii;  MO,  medulla  oblongata.  As  contrasted  with  the 
human  brain,  the  frontal  lobe  is  short  and  small  relatively,  the  fissure  of  Sylvius  is  oblique,  the 
temporo-sphenoidal  lobe  very  prominent,  and  the  external  perpendicular  fissure  very  well  marked. 
(Gratiolet.) 


to  which  there  are  numerous  exceptions,  that  the  brain  weight  corresponds  to  some  extent 
with  the  degree  of  intelligence.  There  can  be  little  doubt  that  the  complexity  and  depth 
of  the  convolutions,  which  indicate  the  area  of  the  gray  matter  of  the  cortex,  correspond 
with  the  degree  of  intelligence. 

The  spinal  cord  of  man  weighs  from  1  to  ij  oz.;  its  weight  relatively  to  the  brain  is 
about  1 :  40  in  the  adult.  As  we  descend  the  animal  scale,  this  ratio  constantly  increases 
till  in  the  mouse  it  is  1 : 4.  In  cold-blooded  animals  the  relation  is  reversed,  the  spinal 
cord  is  the  heavier.     In  the  newt,  1  :o5;  and  in  the  lamprey,  1 :  133. 

The  most  distinctive  points  in  the  human  brain,  as  contrasted  with  that  of  apes,  are: 
1.  The  much  greater  size  and  weight  of  the  whole  brain.  The  brain  of  a  full-grown 
gorilla  weighs  only  about  15  oz.  (450  grms.),  which  is  less  than  J  the  weight  of  the  human 
adult  male  brain,  and  barely  exceeds  that  of  the  human  infant  at  birth.  2.  The  much 
greater  complexity  of  the  convolutions,  especially  the  existence  in  the  human  brain  of 
tertiary  convolutions  in  the  sides  of  the  fissures.  3.  The  greater  relative  size  and  complex- 
ity and  the  blunted  quadrangular  contour  of  the  frontal  lobes  in  man,  which  are  relatively 
broader,  longer,  and  higher  than  in   apes.     In  apes  the  frontal  lobes  project  keel-like 


GENERAL    FUNCTIONS     OF    THE     CEREBRUM  575 

(rostrum)  between  the  olfactory  bulbs.  4.  The  much  greater  prominence  of  the  temporo- 
sphenoidal  lobes  in  apes.  5.  The  fissure  of  Sylvius  is  nearly  horizontal  in  man,  while  in 
apes  it  slants  considerably  upward.     6.  The  distinctness  of  the  fissure  of  Rolando. 

Most  of  the  above  points  are  shown  in  the  accompanying  figure  of  the  brain  of  the 
orang. 

GENERAL  FUNCTIONS  OF  THE  CEREBRUM. 

Evidence  regarding  the  physiology  of  the  cerebral  hemispheres  has 
been  obtained,  as  in  the  case  of  other  parts  of  the  nervous  system,  from  the 
study  of  anatomy,  from  pathology,  and  from  experiments  on  the  lower  animals. 
The  chief  evidences  regarding  the  functions  of  the  cerebral  hemispheres  de- 
rived from  these  various  sources  are  briefly  these:  i,  Any  severe  injury  of 
them,  such  as  a  general  concussion,  or  sudden  pressure  as  by  apoplexy,  may 
instantly  deprive  a  man  of  all  power  of  manifesting  externally  any  mental 
faculty.  2,  In  the  same  general  proportion  as  the  higher  mental  faculties  are 
developed  in  the  vertebrates  and  especially  in  man  at  different  ages,  as  well  as 
in  different  individuals,  the  greater  is  the  development  of  the  cerebral  hemi- 
spheres in  comparison  with  the  rest  of  the  cerebro-spinal  system.  3,  No  other 
part  of  the  nervous  system  bears  a  corresponding  proportion  to  the  development 
of  the  mental  faculties.  4,  Congenital  and  other  morbid  defects  of  the  cerebral 
hemisphere  are,  in  general,  accompanied  by  corresponding  deficiency  in  the 
range  or  power  of  the  intellectual  faculties  and  the  higher  instincts.  5,  Re- 
moval of  the  cerebral  hemispheres  in  the  lower  animals  produces  effects  cor- 
responding with  what  might  be  anticipated  from  the  foregoing  facts. 

Effects  of  the  Removal  of  the  Cerebrum.  The  removal  of  the  cere- 
brum in  the  lower  animals  appears  to  reduce  them  to  the  condition  of  a 
mechanism  without  spontaneity. 

In  the  case  of  the  frog,  when  the  cerebral  lobes  have  been  removed,  the  ani- 
mal appears  similarly  deprived  of  all  power  of  spontaneous  movement.  But 
.it  sits  up  in  a  natural  attitude  and  breathes  quietly.  When  pricked  it  jumps 
away.  When  thrown  into  the  water  it  swims.  When  placed  upon  a  board 
it  remains  motionless,  although,  if  the  board  be  gradually  tilted  over  till  the 
frog  is  on  the  point  of  losing  his  balance,  he  will  crawl  up  till  he  regains  his 
equilibrium,  and  comes  to  be  perched  quite  on  the  edge  of  the  board. 

If  the  frog  be  turned  on  his  back,  he  regains  his  normal  position.  If  his 
back  is  stroked  gently  he  will  utter  the  usual  croaking  sound.  These  activities 
are  carried  on  by  the  normal  frog.  There  is  one  striking  difference,  however, 
between  the  brainless  frog  and  the  normal :  the  former,  if  placed  in  a  position 
and  left  undisturbed,  will  remain  quietly  without  moving  for  an  indefinite  time. 
It  has  apparently  lost  the  power  to  initiate  movements.  Presumably 
any  memory  impressions  or  effects  of  former  experiences  have  been  lost. 
Even  the  more  elemental  stimuli,  which  come  from  tissue  hunger  and  thirst, 
apparently  do   not   affect   the   brainless   frog.     In   other   words,  the  oper- 


576  THE     NERVOUS    SYSTEM 

ation  has  reduced  the  animal  to  the  condition  of  an  automaton  capable  of 
carrying  on  complex  activities,  but  only  after  receiving  some  definite  stimulus. 
This  condition  contrasts  with  that  resulting  from  the  removal  of  the  entire 
brain,  leaving  only  the  spinal  cord.  In  this  case  only  the  simpler  reflex  actions 
can  take  place.  The  frog  does  not  breathe;  he  lies  flat  on  the  table  instead  of 
sitting  up;  when  thrown  into  a  vessel  of  water  he  sinks  to  the  bottom;  when 
his  legs  are  pinched  he  kicks  out,  but  does  not  leap  away. 

If  the  cerebrum  of  the  frog  be  removed,  taking  special  care  not  to  interfere 
with  the  optic  nerves  or  the  optic  thalami,  then  he  acts  somewhat  differently. 
Whereas  with  the  entire  cerebrum  removed  he  makes  no  effort  to  take  food, 
now  he  will  attempt  to  catch  flies  or  other  insects,  and  will  show  other  signs  of 
spontaneous  activity.  He  will  avoid  an  object  and  shows  signs  of  responding 
to  visual  sensations,  such  as  the  attempt  to  feed  just  mentioned. 

The  cerebral  lobes  of  the  frog,  however,  are  very  low  in  the  scale  of  de- 
velopment as  compared  with  other  vertebrates.  The  cortex  is  a  single  layer 
of  rather  small  cells,  and  the  total  volume  of  the  cortex  as  compared  with  other 
portions  of  the  brain  is  small. 

The  case  of  the  pigeon,  which  represents  a  higher  animal  in  the  scale, 
has  been  extensively  studied  by  Flourens  and  others.  They  have  shown  that 
when  the  cerebrum  is  carefully  removed,  leaving  the  basal  nuclei  undisturbed, 
and  the  animal  has  recovered  from  the  immediate  effects  of  the  shock,  it  is 
able  to  carry  on  many  coordinate  activities.  In  the  first  place  it  can  stand 
or  perch  without  difficulty;  if  placed  on  its  back  it  immediately  regains  its 
equilibrium;  if  tossed  in  the  air  it  flies  until  it  comes  in  contact  with  a  firm 
support.  If  disturbed  on  its  perch  it  will  walk  away,  showing  the  power 
to  coordinate  not  only  wing  muscles,  but  the  leg  muscles.  If  left  undisturbed, 
such  a  pigeon  will  occasionally  make  motions,  i.e.,  open  its  eyes,  move  its  head, 
preen  its  feathers,  or  even  take  a  step  or  two.  It  spends  most  of  its  time,  how- 
ever, sitting  quietly  as  though  asleep.  If  aroused,  the  animal  shows  little  or  no 
signs  of  excitement  or  fright. 

After  several  months  such  pigeons  are  said  usually  to  increase  the  motions 
of  spontaneity  or  take  short  flights,  avoiding  obstacles  in  the  way  and  alighting 
definitely  on  the  perch.  They  will  pick  around  among  food  for  definite  articles, 
apparently  intending  to  select  the  food.  £arly  after  the  operation  the  pigeon 
will  pick  at  objects  indiscriminately,  but  does  not  take  food  unless  it  is  placed 
in  the  mouth. 

Apparently  the  main  effect  produced  here  is  to  diminish  the  complexity  and 
efficiency  of  those  activities  which  we  call  spontaneous.  The  surprising  thing 
is  that  there  is  as  little  disturbance  among  the  motor  functions  as  is  found. 

In  mammals  it  is  difficult  to  remove  the  cerebral  hemispheres,  but  in  those 
animals,  in  which  the  operation  has  been  carried  out,  as  for  example  in  the  rab- 
bit and  rat,  a  result  very  similar  to  those  observed  in  the  case  of  the  frog  and 
pigeon  has  been  obtained.     The  animal  is  able  to  maintain  its  equilibrium, 


MOTOR    FUNCTION    OF   THE    CEREBRAL   CORTEX  577 

to  run  or  jump,  and  in  fact  successfully  carry  out  the  most  complicated  coor- 
dinated movements,  but  it  is  unable  to  originate  them  without  stimulation.  In 
the  case  of  the  dog,  it  has  been  found  impossible  to  remove  the  whole  brain 
at  one  operation.  However,  Goltz  has  succeeded  in  removing  both  the 
cerebral  hemispheres  of  the  dog  by  doing  the  operation  in  successive  stages 
and  taking  extraordinary  precautions  to  protect  his  animal  against  the  great 
fall  of  temperature  and  the  immediate  shock  of  the  operation.  He  kept  his 
dos;  alive  for  some  eighteen  months  and  secured  a  complete  recovery  from  the 
series  of  operations.  Goltz's  dog  was  able  to  walk  about,  it  responded  to  a 
bright  light  by  closing  its  eyes,  and  could  be  aroused  by  a  sharp,  loud  sound. 
It  spent  its  time  lying  down  in  the  cage,  sleeping  rolled  up  dog-fashion. 
When  aroused  by  stimulation  of  the  skin,  it  would  move  away  from  the  stim- 
ulating object  and  would  sometimes  growl  and  snap  at  the  object.  If  it  snapped 
at  the  object  it  would  do  so  without  going  toward  it  or  making  the  usual  effort 
to  seize  the  object  which  we  are  accustomed  to  expect  of  a  normal  vicious 
dog.  This  dog  did  not  spontaneously  feed  itself,  but  had  to  have  food  placed 
in  its  mouth  before  it  would  swallow.  But  the  animal  finally  learned  to  take 
food,  as  in  the  case  of  the  pigeon.  This  animal  gave  very  definite  responses 
to  its  condition  of  nourishment;  it  slept  quietly  and  was  peaceful  when  fully 
fed,  but  was  restless  and  irritable  when  hungry. 

Goltz's  dog  showed  complete  absence  of  those  activities  which  we  would 
call  psychic.  That  is  to  say,  it  showed  no  memory  signs,  it  was  unable 
to  learn  the  signal  for  feeding,  it  did  not  manifest  any  fondness  or  signs  of 
pleasure  at  the  presence  of  its  caretaker.  In  short,  there  was  a  complete 
loss  of  memory  and  intelligence,  and  the  animal,  although  performing  some 
activities,  was  in  fact  reduced  to  a  mere  automaton.  It  would  be  difficult  to 
imagine  a  more  crucial  experiment  to  elucidate  the  function  of  the  cerebral 
cortex. 

It  is  quite  evident  that  the  apparatus  for  carrying  out  coordinated  move- 
ments is  in  these  animals  not  localized  either  in  the  cerebrum  or  in  the  spinal 
cord.  It  must  therefore  be  connected  in  some  way  with  the  parts  of  the 
brain  below  the  cerebrum  and  above  the  cord.  There  is  no  reason  why  such 
an  arrangement  may  not  be  supposed  to  exist  in  the  human  brain,  although 
we  must  look  upon  the  cerebrum  as  the  originator  of  voluntary  movements. 

LOCALIZATION  OF  THE  MOTOR  FUNCTION  OF  THE  CERE- 
BRAL CORTEX. 

The  experiments  upon  the  brains  of  various  animals  by  means  of  electrical 
stimulation  have  demonstrated  that  there  are  definite  regions  of  the  cerebral 
cortex  the  stimulation  of  which  produces  definite  movements  of  coordinated 
groups  of  muscles  of  the  opposite  side  of  the  body.  Fritsch  and  Hitzig  were 
the  first  to  show  that  the  cerebral  cortex  responds  to  electric  irritation.  They 
37 


578 


THE     NERVOUS     SYSTEM 


employed  a  weak  constant  current  in  their  experiments,  applying  a  pair  of 
fine  electrodes  not  more  than  one-twelfth  inch  apart  to  different  parts  of 
the  cerebral  cortex.  The  results  thus  obtained  have  been  confirmed  and  ex- 
tended by  Ferrier  and  many  others,  stimulating  chiefly  with  induction  currents. 


Fig.  407. 


Fig.  408. 

Figs.  407  and  408. — Brain  of  Dog,  Viewed  from  Above  and  in  Profile.  F,  Frontal  fissure  some- 
times termed  crucial  sulcus,  corresponding  to  the  fissure  of  Rolando  in  man;  5,  fissure  of  Sylvius, 
around  which  the  four  longitudinal  convolutions  are  concentrically  arranged;  1,  flexion  of  head 
on  the  neck,  in  the  median  line;  2,  flexion  of  head  on  the  neck,  with  rotation  toward  the  side  of  the 
stimulus;  3,  4,  flexion  and  extension  of  anterior  limb;  5,  6,  flexion  and  extension  of  posterior 
limb;  7,  8,  9,  contraction  of  orbicularis  oculi  and  the  facial  muscles  in  general.  The  unshaded  part 
is  that  exposed  by  opening  the  skull.      (Dalton.) 


The  fundamental  phenomena  observed  in  all  these  cases  may  be  thus 
epitomized: 

1.  Excitation  of  the  same  spot  on  the  cortex  is  always  followed  by  the  same 
movement  in  the  same  animal.     2.  The  area  of  excitability  for   any  given 


MOTOR  FUNCTION  OF  THE  CEREBRAL  CORTEX  579 

movement  is  extremely  small,  and  admits  of  very  accurate  definition.  3.  In 
different  animals  excitations  of  anatomically  corresponding  spots  produce 
contractions  in  similar  or  corresponding  muscles. 

The  various  definite  movements  resulting  from  the  electric  stimulation 
of  circumscribed  areas  of  the  cerebral  cortex  are  enumerated  in  the  description 
of  the  accompanying  figures  of  the  dog's  and  monkey's  brains. 

In  the  case  of  the  dog  the  results  obtained  are  summed  up  as  follows  by 
Hitzig:  1,  One  portion,  anterior,  of  the  convexity  of  the  cerebrum  is  motor; 
another  portion,  posterior,  is  non-motor.  2,  Electric  stimulation  of  the  motor 
portion  produces  coordinated  muscular  contraction  on  the  opposite  side  of  the 
body.  3,  With  very  weak  currents,  the  contractions  produced  are  distinctly 
limited  to  particular  groups  of  muscles;  with  stronger  currents  the  stimulus 
is  communicated  to  other  muscles  of  the  same  or  neighboring  parts.  4,  The 
portions  of  the  brain  intervening  between  these  motor  centers  are  inexcitable. 

Following  strong  stimulation  of  cortical  motor  centers  other  groups  of 
muscles  than  those  innervated  by  the  centers  stimulated  may  also  take  part  in 
the  contractions. 

According  to  the  observations  of  Ferrier,  confirmed  and  extended  by  later 
experimenters,  stimulation  of  various  parts  of  the  monkey's  brain,  as  indicated 
by  the  numbers  in  figures  409,  410,  produces  movements  of  definite  muscles, 
thus:  Stimulation  of  the  district  marked  1  causes  movement  of  hind  foot; 
of  2,  chiefly  adduction  of  the  foot;  of  3,  movements  of  hind  foot  and  tail; 
of  4,  of  latissimus  dorsi ;  of  5,  extension  forward  of  arm;  a,  b,  c,  d,  movements  of 
hand  and  wrist;  of  6,  supination  and  flexion  of  forearm;  of  7,  elevation  of  the 
upper  lip;  of  8,  conjoint  action  of  elevation  of  upper  lip  and  depression  of 
lower;  of  9,  opening  of  mouth  and  protrusion  of  tongue;  of  10,  retraction  of 
tongue;  of  n,  action  of  platysma;  of  12,  elevation  of  eyebrows  and  eyelids, 
dilatation  of  pupils,  and  turning  head  to  opposite  side;  of  13,  eyes  directed  to 
opposite  side  and  upward,  with  usually  contraction  of  the  pupils;  of  13',  similar 
action,  but  eyes  usually  directed  downward;  of  14,  retraction  of  opposite  ear, 
head  turns  to  the  opposite  side,  the  eyes  widely  opened  and  pupils  dilated;  of 
15,  stimulation  of  this  region,  which  corresponds  to  the  tip  of  the  uncinate 
convolution,  causes  torsion  of  the  lip  and  nostril  of  the  same  side. 

It  is  thus  seen  that  the  motor  areas  chiefly  correspond  with  the  ascending 
frontal  and  ascending  parietal  convolutions,  and  that  the  movements  of  the  leg 
are  represented  at  the  upper  part  of  these  convolutions,  then  follow  from  above 
downward  the  centers  for  the  arms,  the  face,  the  lips,  and  the  tongue. 

According  to  the  further  researches  of  Schafer  and  Horsley,  electrical  stim- 
ulation of  the  marginal  convolution  internally  at  the  parts  corresponding  with 
the  ascending  frontal  and  parietal  convolutions,  from  the  front  backward, 
produces  movements  of  the  arm,  of  the  trunk,  and  of  the  leg. 

A  good  deal  of  doubt  was  thrown  upon  the  experiments  of  Ferrier  by  Goltz 
and  other  observers,  from  the  results  of  excising  the  so-called  motor  areas  of 


580 


THE     NERVOUS     SYSTEM 


the  dog's  brain.     It  was  found  that  the  part  might  be  sliced  away  or  washed 
away  with  a  stream  of  water,  but  that  no  permanent  paralysis  ensued. 

More  extensive  observations,  however,  have  confirmed  Ferrier's  original 
statement,  at  any  rate  with  regard  to  the  monkey's  brain.     Destruction  of  the 


Fig.  409. 


Fig.  410. 

Figs.  409  and  410. — Diagrams  of  Monkey's  Brain  to  Show  the  Effects  of  Electric  Stimulation 
of  Certain  Spots.      (According  to  Ferrier.) 


motor  areas  for  the  arm  produces  some  permanent  paralysis  of  the  arm  of 
the  opposite  side,  and  similarly  of  that  for  the  leg,  paralysis  of  the  opppsite 
leg.  If  both  areas  are  destroyed,  permanent  hemiplegia  ensues.  Paralysis 
of  so  extensive  and  permanent  a  character  does  not,  however,  appear  the 
rule  when  the  brain  of  a  dog  is  used  instead  of  that  of  the  monkey.  It  is 
suggested  that  in  the  animal  lower  in  the  scale  the  functions  which  in  the 


MOTOR    AREAS    OF    THE    HUMAN    BRAIN 


581 


monkey  are  discharged  by  the  cortical  centers  may  be  subserved  to  a  greater 
extent  by  the  basal  ganglia. 

Motor  Areas  of  the  Human  Brain.     It  is  naturally  of  great  impor- 
tance to  discover  how  far  the  results  of  experiments  upon  the  dog  and  monkey 


Fig.   411. — Motor  Areas  of  the  Human  Brain,  Lateral  View. 


Fig.  412. — Motor  Areas  of  the  Human  Brain,  Median  View. 

hold  good  with  regard  to  the  human  brain.  Evidence  furnished  by  diseased 
conditions  is  not  wanting  to  support  the  general  idea  of  the  existence  of  cortical 
motor  centers  in  the  human  brain,  figure  411. 

So  far,  however,  it  has  been  possible  to  localize  motor  functions  in  the 
precentral  and  ascending  parietal  convolutions  only;   the  convolutions  which 


582 


THE     NERVOUS    SYSTEM 


bound  the  fissure  of  Rolando  and  those  on  the  inner  side  of  the  hemispheres 
which  correspond  thereto,  and  possibly  the  frontal  lobe  in  front  of  the  pre- 
central  convolution. 

The  position  of  the  centers  is  probably  much  the  same  as  in  the  monkey's 
brain,  those  for  the  leg  above,  those  for  the  arm,  face,  lips,  and  tongue  from 
above  downward.  Destruction  of  these  parts  causes  paralysis,  corresponding 
to  the  district  affected,  and  irritation  causes  contractions  of  the  muscles  of  the 


CORP.  CALIOSUM 


-ANT"?  LIMB 
INTVCAPSULF 


corp:gen  :int. 

SUP  QUADtBODV 


TEMPORO  -PONTINE 
TRACT 


LOBE. 


Fig.  413. — Diagram  of  Certain  Connections  of  the  Frontal,  Temporal,  and  Occipital  Lobes. 
Founded  on  the  observations  of  Flechsig,  Ferrier,  and  Turner.      (Cunningham.) 


same  part.  Again,  a  number  of  cases  are  on  record  in  which  aphasia,  or  the 
loss  of  power  of  expressing  ideas  in  words,  has  been  associated  with  disease  of 
the  posterior  part  of  the  lower  or  third  frontal  convolution  on  the  left  side. 
This  condition  is  usually  associated  with  paralysis  of  the  right  side,  right 
hemiplegia. 

This  district  of  the  brain,  particularly  the  convolutions  bounding  the 
fissure  of  Rolando,  is  now  generally  known  as  the  motor  area;  and  there  is  no 
doubt  whatever  that  from  this  area  pass  the  nerve  fibers  which  proceed  to  the 
spinal  cord,  and  are  there  represented  as  the  pyramidal  tracts. 


MOTOR    AREAS     OF    THE     HUMAN     BRAIN 


583 


This  is  the  reason  that  movements  are  produced  on  stimulation  of  the  white 
matter  after  the  superficial  gray  matter  of  the  animal's  brain  has  been  sliced  off. 

These  motor  fibers  are  those  which  arise  from  the  pyramidal  cells  of  the 
cortex.  From  the  motor  area  of  the  cortex  they  converge  to  the  internal  cap- 
sules, and  pass  down  to  the  crus.  In  the  internal  capsule  the  fibers  which  pass 
to  the  pyramidal  tracts  of  the  spinal  cord  occupy  that  part  known  as  the  knee 
(genu)  and  the  anterior  two-thirds  of  the  posterior  limb,  figure  414.  In  this 
district  the  fibers  for  the  face,  arm,  and  leg  are  in  this  relation:  those  for  the 
face  and  tongue  are  just  at  the  knee,  and  below  or  behind  them  come  first  the 
fibers  for  the  arm  and  then  those  for  the  leg. 

The  more  accurately  known  arrangements  of  these  fibers  in  the  monkey's 
brain,  named  in  order,  from  above  down,  are  those  for  the  eye,  head,  tongue, 


Fig.  414. — Diagram  to  Show  the  Relative  Positions  of  the  Several  Motor  Tracts  in  Their 
Course  from  the  Cortex  to  the  Crus.  The  section  through  the  convolution  is  vertical;  that  through 
the  internal  capsule,  IC,  horizontal;  that  through  the  crus  again  vertical.  CN,  caudate  nucleus; 
O  TH,  optic  thalamus;  L2  and  L3,  middle  and  outer  part  of  lenticular  nucleus;  f,  a,  /,  face,  arm, 
and   leg   fibers.     The  words  in  italics  indicate  corresponding  cortical  centers.      (Gowers.) 


mouth,  shoulder,  elbow,  digits,  abdomen,  lip,  knee,  digits.  These  fibers  come 
for  the  most  part  from  the  portion  of  the  cortex  on  either  side  of  the  fissure  of 
Rolando,  but  chiefly  from  the  anterior  central  gyrus,  hence  called  the  Rolan- 
dic  area.  But  the  areas  for  the  head  and  eyes  lie  more  anteriorly  in  the 
frontal  lobe,  to  the  front  of  the  precentral  sulcus — that  for  the  head  above 
that  for  the  eyes,  and  an  area  for  the  trunk  (not  indicated  in  the  figure  414) 
is  situated  more  toward  the  middle  line  of  the  hemisphere,  internal  to  that  for 
the  leg.  Those  fibers,  passing  between  the  occipital  lobe  and  the  optic  thal- 
amus and  superior  corpora  quadrigemina,  are  concerned  with  vision,  and  are 
called  fibers  of  the  optic  radiation.  In  like  manner,  from  the  inferior  cor- 
pora quadrigemina  and  the  internal  geniculate  bodies,  fibers  which  make 
up  the  auditory  radiation  pass  to  the  auditory  center. 


584 


THE     NERVOUS    SYSTEM 


It  has  already  been  shown  that  the  motor  fibers  of  the  internal  capsule  of 
one  side  cross  over  to  the  opposite  side  in  the  decussation  of  the  pyramids  in 
the  medulla.  This  decussation  is  not  quite  complete,  as  some  fibers  pass 
down  on  the  same  side  in  the  direct  pyramidal  tract.  A  small  portion  of  these 
direct  fibers  end  around  the  motor  neurones  of  the  same  side,  but  the  great 
majority  cross  to  the  opposite  side  in  the  anterior  commissure  at  some  lower 
level  of  the  cord.  It  follows  that  the  motor  areas  of  the  cortex  on  one  side 
control  the  muscular  movements  of  the  opposite  side  of  the  body,  but  to  a  slight 
extent  those  of  the  same  side.  Disease  in  the  region  of  the  fissure  of  Rolando 
is  usually  accompanied  by  a  disturbance  of  the  motor  function  on  the  opposite 
side  of  the  body,  although  there  is  some  slight  motor  disturbance  on  the  same 
side. 


LOCALIZATION    OF   SENSORY    FUNCTION   IN   THE    CEREBRAL 

CORTEX. 

There  is  evidence  that  fibers  from  the  nerves  of  special  sense  are  specially 
connected  with  definite  and  distinct  parts  of  the  cerebral  cortex. 

The  fibers  from  the  sensory  nerves,  we  have  found,  are  connected  with  the 
cerebral  cortex  by  a  chain  of  neurones.  These  sensory  paths,  although  com- 
plex, are  definite  and  distinct.  Their  cortical  connections  have  been  mapped 
out  with  considerable  definiteness. 

The  Body  Sensory  or  Somesthetic  Area.  The  motor  function  around 
the  fissure  of  Rolando  for  a  long  time  obscured  the  fact  that  this  region, 


.^AESTHETIC  jHFt 


.•v*£Til 


Fig. 


415- — Diagrams  to  Show  Flechsig's  Sensory  and  Association  Areas  on  t  e  Surface  of  the 
Cerebral  Hemisphere.      (From  Cunningham,  after  Flechsig.) 


especially  the  post-central  convolution,  is  intimately  connected  with  the 
perception  of  general  body  sensations.  Physiological  and  pathological  ob- 
servations supported  this  view,  and  recently  Flechsig  has  much  strengthened 
the  view  by  his  method  of  studying  the  progressive  development  of  the  brain. 
In  figure  415  we  produce  Flechsig's  diagram  showing  the  body  sensory  (som- 
esthetic) area.     The  borders  of  the  area  are  more  or  less  indefinite  and  less 


VISUAL    OR     OPTIC     CENTER  585 

distinct  than  the  main  portion.  This  is  indicated  by  the  lighter  shading. 
Lesions  of  this  area  in  the  cortex  lead  to  loss  of  sensibility  in  definite  regions  of 
the  opposite  side  of  the  body. 

Visual  or  Optic  Center.  The  termination  of  the  optic  nerve  in  each 
eye,  the  retina,  to  the  structure  of  which  we  shall  return  when  treating  of  the 
eye,  is  so  arranged  that  when  we  look  at  an  object  with  both  eyes,  symmetrical 
parts  of  each  retina  are  used.  For  example,  if  we  look  at  an  object  to  the  left, 
an  image  of  that  object  is  focussed  upon  the  right  half  of  both  retinae,  viz., 
upon  the  temporal  side  of  the  right  retina,  and  upon  the  nasal  side  of  the  left 
retina.  The  optic  nerve  fibers  of  these  symmetrical  parts  of  the  retina  are 
gathered  together  behind  where  the  optic  nerves  decussate,  viz.,  in  the  optic 
chiasma.  The  fibers  which  come  from  the  right  side  of  both  eyes  are  contained 
in  the  optic  tract  of  the  same  side,  viz.,  the  right,  those  from  the  right  eye  being 
outside  of  the  others.  In  the  same  way  the  left  optic  tract  contains  internally 
fibers  from  the  left  side  of  the  right  eye  and  externally  those  from  the  left 
side  of  the  left  eye.  The  optic  tract  thus  formed  then  passes  backward  and 
terminates  in  three  distinct  nuclei,  viz.,  the  pulvinar  of  the  optic  thalamus, 
the  anterior  corpus  quadrigeminum,  and  the  lateral  corpus  geniculatum. 
These  nuclei  atrophy  if  the  eyes  are  removed  from  an  adult  animal;  and  if 
the  eyes  are  removed  from  a  newly  born  animal,  they  do  not  fully  develop. 
Through  the  superior  corpora  quadrigemina  the  optic  tract  establishes  synap- 
ses that  bring  it  into  relation  with  the  nucleus  of  the  third  nerve,  and  which 
form  the  basis  of  the  eye  reflexes  to  light  stimulation. 

It  appears  that  some  of  the  fibers  of  the  optic  tract  pass  directly  into  the 
cerebral  cortex  without  joining  with  the  optic  thalamus,  corpus  quadrigeminum, 
or  corpus  geniculatum. 

It  was  shown  above  that  the  fibers  of  the  cerebral  cortex,  known  as  the 
optic  radiation,  pass  from  the  occipital  region  to  the  three  nuclei  about 
which  we  are  speaking,  viz.,  into  the  pulvinar  of  the  optic  thalamus,  the  anterior 
corpus  quadrigeminum,  and  lateral  corpus  geniculatum,  and  it  is  known  that 
when  the  occipital  cortex  is  removed,  these  three  atrophy.  It  has  been  further 
shown  that  in  a  newly  born  animal  the  removal  of  such  a  region  is  followed 
by  imperfect  development  of  the  parts  in  question. 

If  one  optic  nerve  be  divided,  blindness  of  the  corresponding  eye  results ; 
but  if  one  optic  tract  be  divided  there  is  a  half  blindness  in  both  eyes,  which  is 
called  hemianopsia,  or  hemiopia,  right  or  left,  according  as  the  right  or  left  field 
of  vision  is  cut  off.  It  is  evident  that  the  occipital  lobe,  figures  412,  413,  and 
particularly  the  cuneus,  is  concerned  as  a  visual  center,  since  not  only  is  it 
connected  with  the  optic  nerves,  as  we  have  seen,  but  also  because  the  re- 
moval of  the  right  occipital  lobe  in  an  animal  (monkey)  is  followed  by  left 
hemiopia,  removal  of  the  left  by  right  hemiopia,  and  removal  of  both  occipital 
lobes  by  total  blindness. 

Olfactory  Center  in  the  Cortex.     The  olfactory  nerve  differs  from 


586 


THE     NERVOUS     SYSTEM 


the  other  cranial  nerves.  In  reality  it  is  a  representative  of  the  olfactory  lobes 
of  other  animals,  which  are  part  of  the  cerebrum.  The  olfactory  lobe  origi- 
nates as  an  offshoot  from  the  cerebral  vesicle,  the  front  part  of  which  is  de- 
veloped into  the  bulb  of  the  olfactory  nerve,  while  the  back  part  forms  its 
peduncle.  The  nerve,  the  cavity  of  which  in  man  is  filled  up  in  the  fully  de- 
veloped condition  with  neurogliar  substance,  lies  upon  the  cribriform  plate 
of  the   ethmoid  bone,  and  is    contained  in  a    groove  on  the  under  surface 


:ORP.GEN.INT. 


Fig.   416. — Scheme  of  the  Central  Connections  of  the  Optic  Fibers.      (Cunningham.) 


of  the  frontal  lobe.  On  examination  of  the  bulb  it  is  found  to  be  thus  made 
up:  Beneath  the  neurogliar  layer  is  a  layer  of  longitudinal  fibers  and  a  few 
nerve  cells  next  to  this  is  a  layer  of  small  cells,  nuclear  layer,  fibers  from  the 
layer  of  nerve  fibers  passing  through  it. 

The  nuclear  layer  is  also  separated  into  groups  of  cells  by  an  interlacing 
of  the  fibers.  The  next  layer  is  thick  and  is  composed  of  neuroglia  and  nerve 
fibers,  some  of  which  are  medullated,  as  well  as  of  cells  more  or  less  pyramidal 
in  shape.  Below  this  layer  is  the  layer  of  olfactory  glomeruli.  These  glomer- 
uli are  small  synapses  of  olfactory  fibers.     The  larger  also  includes  small 


TASTE  CENTER  OF  THE  CORTEX  587 

cells  and  granular  matter.  A  full  description  of  the  anatomy  of  these  parts 
is  given  later. 

Fibers  of  the  olfactory  nerve  proper  are  found  below  this  layer,  and  pass 
through  the  cribriform  plate  to  be  distributed  to  the  olfactory  mucous  mem- 
brane. They  arise  from  cells  in  the  olfactory  mucous  membrane,  and  end  in 
the  glomeruli.  The  peduncle  of  the  nerve  or  the  olfactory  tract,  as  it  is  some- 
times called,  is  made  up  of  longitudinal  fibers  originating  in  the  bulb,  with 
neuroglia  and  some  nerve  cells. 

The  fibers  of  the  olfactory  tract  have  been  traced  into  the  nucleus  amygdala' 
and  its  junction  with  the  hippocampal  gyrus  in  the  temporal  lobe,  figure  399. 
The  hippocampus  must  be  in  some  way  connected  with  smell,  since  a  lesion  of 
it,  leaving  the  olfactory  tract  uninjured,  seriously  interferes  with  that  sense. 

Taste  Center  of  the  Cortex.,  It  is  very  uncertain  where  the  taste 
center  is  situated,  if  such  exist.  It  has  been  placed  in  the  anterior  portion  of 
the  inferior  temporal  convolution,  not  far  from  that  of  smell,  figure  399. 

Auditory  Center  in  the  Cortex.  This  center  has  been  localized  in 
the  superior  temporal  convolution.  Experiments  have  been  made  which 
connect  auditory  impulses  on  either  side  with  the  inferior  corpus  quadrige- 
minum  and  the  median  corpus  geniculatum,  for  when  the  internal  ear  is 
destroyed  there  results  atrophy  of  these  bodies  as  well  as  of  the  lateral 
fillet  of  the  opposite  side.  On  the  other  hand,  destruction  of  the  part  of  the 
temporal  lobe  above  indicated  is  similarly  followed  by  atrophy  of  the  nuclei 
of  the  same  side.  These  nuclei  bear  much  the  same  relation  to  the  sense 
of  hearing  as  do  the  anterior  corpora  quadrigemina  and  the  lateral  corpora 
geniculata  to  the  sense  of  sight,  figures  389  and  416. 

ASSOCIATION  CENTERS  OF  THE  CEREBRAL   CORTEX. 

The  theory  of  localization  of  the  function  of  different  parts  of  the  cerebral 
cortex  has  received  substantial  support  from  the  study  of  the  motor  and  the 
sensory  areas  in  man  and  the  mammals.  But  when  the  exploration  of  the 
cortex  is  complete  and  the  motor  and  sensory  areas  are  bounded  as  definitely 
as  may  be,  there  still  remain  great  areas  in  which  stimulation  is  apparently  non- 
effective so  far  as  our  present  means  of  interpretation  reveal.  Traumatic 
and  pathological  lesions  produce  no  sensory  or  motor  disturbances.  The 
areas  of  this  class  which  are  most  extensive,  i.e.,  which  cover  the  greatest 
amount  of  cortex,  are  three  in  number — the  frontal  lobe,  the  parietal  lobe,  and 
a  large  part  of  the  temporal  lobe  below  the  superior  temporal  convolution. 

Flechsig  has  made  a  study  of  the  development  of  the  human  brain,  paying 
especial  attention  to  the  progressive  development  of  the  great  tracts  of  fibers. 
He  has  shown  that  the  tracts  appear  in  a  certain  order  of  sequence,  also  that 
the  myelinization  takes  place  progressively.  On  the  assumption  that  ef- 
fective functionization  is  acquired  with  the  myelin  sheath,  he  showed  a  close 


588 


THE     NERVOUS     SYSTEM 


correspondence  in  time  between  the  development  of  the  tracts  and  the  mani- 
festation of  functions  known  to  involve  the  tracts  in  question.  The  great 
somesthetic  area  and  its  tracts  are  first  to  develop ;  then  tracts  to  the  occipital  or 
visual  center,  to  the  auditory  and  other  sensory  centers,  and,  finally,  to  these 
great  areas  whose  functions  remain  obscure. 

Basing  his  deductions  on  the  facts  of  development,  on  the  isolated  cases  of 
lesion  and  disease,  and  on  the  careful  comparative  studies  of  the  brains  of  cer- 
tain men  of  unusual  intellectual  powers,  whose  personal  characteristics  and 


Fig.  417. — The  Association  Fibers  in  the  Centrum  Ovale.  A,  Between  adjacent  convolutions; 
B,  between  frontal  and  occipital  lobes;  C,  between  frontal  and  temporal  lobes,  the  cingulum;  D, 
between  temporal  and  frontal  lobes — lesion  of  this  tract  causes  paraphasia;  E,  between  occipital 
and  temporal  lobes — lesion  of  this  tract  causes  word-blindness;  C.N,  caudate  nucleus;  O.T, 
eptic  thalamus. 


intellectual  genius  are  known,  Flechsig  has  advanced  the  hypothesis  that  the 
areas  of  the  cortex  not  concerned  directly  with  motor  or  sensory  functions  are 
association  areas. 

The  Association  Centers  of  Flechsig.  The  great  association  centers 
are  the  frontal,  parietal,  and  temporal,  figure  415.  These  regions  of  the  cor- 
tex are  apparently  not  directly  connected  with  tracts  of  the  brain  stem  and 
cord,  but  they  are  richly  connected  with  the  areas  that  do  have  connection  with 
the  cord.  Short  association  fibers  connect  neighboring  convolutions  within 
the  centers,  fibers  which  are  chiefly  the  axones  of  the  polymorphous  cells  of  the 
fourth  layer  of  the  cortex.  Long  association  fibers  run  from  one  center  to 
another,  such  as  the  cingulum,  superior  and  inferior  longitudinal  fasciculi, 
etc.  The  longer  connectives  run  from  association  to  association  centers, 
and  from  association  to  sensory  and  motor  centers.  Flechsig  believes  that 
the  sensory  centers  are  not  connected  directly  with  each  other,  but  only  in- 
directly through  the  association  areas. 

Cases  of  injury  and  of  disease  of  the  human  brain  in  the  association  areas 
are  not  numerous,  but  such  as  there  are  tend  to  confirm  Flechsig's  hypothesis 
that  the  function  of  these  areas  is  that  of  the  higher  psychic  activity. 


THE     ANTERIOR    OR     FRONTAL    ASSOCIATION     CENTER  589 

The  Anterior  or  Frontal  Association  Center.  The  frontal  area  is 
more  closely  connected  with  the  motor  areas  and  the  centers  for  the  somesthetic 
sense.  With  injury  to  this  area  the  individual  shows  weakness  in  attention, 
in  reflection,  and  in  control  over  the  expressions  of  anger,  self-appreciation, 
and  other  activities  that  are  expressive  of  personal  volitions  and  emotions. 

The  American  crowbar  case  is  a  classical  instance  of  lesion  of  the  frontal 
lobe.  A  young  man  of  twenty-five  had  an  iron  bar,  an  inch  and  a  quarter 
in  diameter  and  over  three -feet  long,  driven  through  his  skull  and  brain 
by  the  premature  explosion  of  a  blast  of  powder.  He  not  only  recovered, 
but  lived  for  twelve  years  afterward.  At  the  post-mortem  examination  the 
puncture  was  found  to  be  through  the  prefrontal  lobe,  anterior  to  the  coronal 
suture. 

This  man  was  considered  a  most  efficient  workman  and  foreman  before 
the  injury.  After  his  recovery  he  was  fitful,  impatient  of  restraint,  capricious, 
obstinate;  was  most  inconsiderate  of  his  associates,  profane,  passionate; 
from  a  shrewd  business  man  he  was  changed  to  the  intellectual  level  of  a 
child  and  was  regarded  by  his  associates  as  mentally  unbalanced. 

A  summary  of  fifty  cases  of  pathological  lesions  of  the  prefrontal  areas  of 
the  human  brain  is  given  by  Williamson.  The  mental  traits  of  thirty-two  are 
summarized  in  the  following  terms:  "A  condition  of  mental  decadence;  a 
dull  mental  state;  loss  of  power  of  attention;  loss  of  memory;  loss  of  spon- 
taneity; the  patient  takes  no  heed  of  his  surroundings;  sleeping  during  the 
greater  part  of  the  day.,  or  remaining  semi-comatose."  Yet  these  patients  are 
able  to  walk  about  and  execute  well  coordinated  muscular  activities  of  all 
kinds  that  do  not  involve  complex  intellectual  activity. 

The  Parietal  Association  Centers.  Special  mention  is  made  of  this 
association  area  because  there  is  increasing  evidence  that  it  is  the  parietal 
region  of  the  brain,  rather  than  the  frontal,  as  popularly  believed,  that  is 
most  intimately  concerned  with  acts  and  powers  of  imagination,  idealization, 
and  reasoning.  It  is  the  region  through  which  the  individual  maintains  his 
interests  and  relations  with  the  external  world  as  against  his  own  body.  The 
parietal  association  center  is  more  closely  related  to  the  visual,  auditory,  and 
speech  centers  of  the  cortex.  The  great  musician  Bach  had  an  exception- 
ally well  developed  parietal  region. 

On  the  Cortical  Centers  in  General.  For  purposes  of  clearness 
in  presentation,  the  cortical  centers  have  been  discussed  one  by  one,  but  the 
/eader  is  guarded  against  the  thought  that  their  activities  are  in  any  sense 
isolated.  A  motor  area  does  not  usually  act  in  the  absence  of  sensory  or  af- 
ferent stimulation  in  the  actual  living  body,  whether  it  may  do  so  on  occasion 
or  not.  Neither  do  sensory  impressions  arising  in  the  peripheral  sense  organ 
make  their  way  over  definite  tracts  to  the  brain  and  cortex  and  arouse  sensa- 
tions alone.  Sensations  do  not  occur  independent  of  motor  activities  on  the 
one  hand,  and  of  intellectual  acts  through  the  association  centers  on  the  other. 


590  THE     NERVOUS    SYSTEM 

The  association  centers  are  the  highest  coordinating  regions  of  the  nervous 
system.  They  are  to  the  sensory  and  motor  centers  what  these  latter  are  to 
the  reflex  centers  of  the  cord,  the  difference  being  one  of  degree  and  not  of 
kind.  Further,  they  are  probably  set  into  activity  by  the  complex  of  in- 
flowing or  afferent  impulses  in  just  the  same  sense  that  the  spinal  reflex  cen- 
ters are  set  in  activity  by  sensory  or  afferent  stimuli;  the  condition  is,  of  course, 
a  thousand  times  more  complex. 

THE  PHYSIOLOGY  OF  SLEEP. 

All  parts  of  the  body  which  are  the  seat  of  active  change  require  periods  of 
rest.  The  alternation  of  work  and  rest  is  a  necessary  condition  of  their  main- 
tenance and  of  the  healthy  performance  of  their  functions.  These  alternating 
periods,  however,  differ  much  in  duration  in  different  cases;  but,  for  any  in- 
dividual instance,  they  preserve  a  general  and  rather  close  uniformity.  Thus, 
the  periods  of  rest  and  work  mentioned,  in  the  case  of  the  heart,  occupy,  each 
of  them,  about  half  a  second;  in  the  case  of  the  ordinary  respiratory  muscles 
the  periods  are  about  four  or  five  times  as  long.  In  many  cases  (as  of  the 
voluntary  muscles  during  violent  exercise),  while  the  periods  during  active 
exertion  alternate  very  frequently,  yet  the  expenditure  goes  far  ahead  of  the 
repair,  and,  to  compensate  for  this,  an  after-repose  of  some  hours  becomes 
necessary,  the  rhythm  being  less  perfect  as  to  time  than  in  the  case  of  the 
muscles  concerned  in  circulation  and  respiration. 

Obviously,  it  would  be  impossible  that,  in  the  case  of  the  brain,  there 
should  be  short  periods  of  activity  and  repose,  or,  in  other  words,  of  conscious- 
ness and  unconsciousness.  The  repose  must  occur  at  long  intervals  and  must 
be  proportionately  long.  Hence  the  necessity  for  that  condition  which  we  call 
Sleep;  a  condition  which,  seeming  at  first  sight  exceptional,  is  only  an  unusually 
perfect  example  of  what  occurs,  at  varying  intervals,  in  every  actively  working 
portion  of  our  bodies. 

By  exposing,  at  a  circumscribed  spot,  the  surface  of  the  brain  of  a  living 
animal,  and  protecting  the  exposed  part  by  a  watch-glass,  Durham  was  able 
to  prove  that  the  brain  becomes  visibly  paler,  anemic,  during  sleep;  and  the 
anemia  of  the  optic  disc  during  sleep,  observed  by  Hughlings  Jackson,  may 
be  taken  as  a  strong  confirmation,  by  analogy,  of  the  same  fact. 

The  Circulation  During  Sleep.  Blood  is  supplied  to  the  brain  in 
four  distinct  but  anastomosing  arteries.  This  efficient  anatomical  arrange- 
ment is  obviously  all  the  more  important  when  it  is  remembered  that  the  cir- 
culation in  the  brain  has  no  local  device  for  regulating  the  blood-flow,  but  that 
it  must  depend  on  the  variations  in  general  blood  pressure.  Any  variation  in 
the  flow  of  blood  in  the  brain  depends  on  changes  in  general  blood  pressure; 
changes  which  are  themselves  dependent  on  variations  in  the  activity  of  the 
heart,  the  caliber  of  the  blood-vessels,  etc.,  discussed  on  page  186. 


SOMNAMBULISM    AND     DREAMS  591 

Howell  and  others  have  studied  the  circulation  by  the  plethysmography 
method  during  sleep.  The  results  show  that  with  the  loss  of  consciousness,  and 
immediately  following,  there  is  a  sharp  dilatation  of  the  blood-vessels  of  the 
arm,  probably  chiefly  of  the  skin,  as  shown  by  the  increase  in  volume.  The 
vessels  remain  dilated  until  the  individual  begins  to  awaken,  when  there  is 
a  rapid  constriction  with  decrease  of  volume  of  the  organ. 

The  dilatation  of  the  general  blood-vessels  draws  off  the  supply  of  blood 
from  the  brain,  and  the  resulting  partial  anemia  contributes  to  loss  of  conscious- 
ness. The  blood  supply  is  ample  for  growth  and  repair  and  rest  of  the  nervous 
system.  How  efficient  this  rest  period  is  for  the  rejuvenation  of  the  nervous 
tissue  is  indicated  even  by  the  relatively  gross  means,  figure  356,  shown  in 
the  histological  preparations  of  nerve  cells. 

Somnambulism  and  Dreams.  What  we  term  sleep  occurs  often  in  very  different 
degrees  in  different  parts  of  the  nervous  system;  and  in  some  parts  the  expression  cannot 
be  used  in  the  ordinary  sense. 

The  phenomena  of  dreams  and  somnambulism  are  examples  of  differing  degrees  of  sleep 
in  different  parts  of  the  cerebro-spinal  nervous  system.  In  the  former  case  the  cerebrum 
is  still  partially  active;  but  the  activity  is  no  longer  corrected  by  the  reception,  on  the  part 
of  the  sleeping  sensorium,  of  impressions  of  objects  belonging  to  the  outer  world;  neither 
can  the  cerebrum,  in  this  half-awake  condition,  act  on  the  centers  of  reflex  action  of  the  vol- 
untary muscles,  so  as  to  cause  the  latter  to  contract — a  fact  within  the  painful  experience 
of  all  who  have  suffered  from  nightmare. 

In  somnambulism  the  highei  centers  are  capable  of  coordinating  that  train  of  reflex 
nervous  action  which  is  necessary  for  progression,  while  the  nerve  center  of  the  muscular 
equilibrium  sense  (in  the  cerebellum?)  is,  presumably,  fully  awake;  but  the  sensorium 
is  still  asleep,  and  impressions  made  on  it  are  not  sufficiently  felt  to  rouse  the  cerebrum 
to  a  comparison  of  the  difference  between  mere  ideas  or  memories  and  sensations  derived 
from  external  objects. 

VI.  THE  SYMPATHETIC  SYSTEM. 

The  fact  has  already  been  emphasized  that  the  sympathetic  system  of 
nerves  is  an  organic  and  constituent  part  of  the  nervous  system. 

Organization  and  Distribution.  The  sympathetic  system  consists 
of  those  collections  of  nerve  cells  or  ganglia  lying  outside  of  the  brain  and 
cord  (exclusive  of  the  root  ganglia),  and  the  nerve  tracts  connecting  them 
with  one  another  and  with  the  cerebro-spinal  axis.  Its  parts  that  should  be 
mentioned  are :  1,  a  double  chain  of  ganglia  and  fibers,  which  extends  from  the 
cranium  to  the  pelvis,  along  each  side  of  and  in  front  of  the  vertebral  column, 
and  from  which  branches  are  distributed  both  to  the  cerebro-spinal  system 
and  to  other  parts  of  the  sympathetic  system.  With  these  may  be  included  the 
small  ganglia  in  connection  with  those  branches  of  the  fifth  cerebral  nerve 
which  are  distributed  in  the  neighborhood  of  the  organs  of  special  sense, 
namely,  the  ophthalmic,  otic,  sphenopalatine,  and  submaxillary  ganglia. 
2,  Various  ganglia  and  plexuses  of  nerve  fibers  which  give  off  branches  to  the 
thoracic  and  abdominal  viscera,  the  chief  of  such  plexuses  being  the  cardiac, 


592 


THE    NERVOUS    SYSTEM 


solar,  and  hypogastric;  but  in  intimate  connection  with  these  are  many 
secondary  plexuses,  as  the  aortic,  spermatic,  and  renal.  Fibers  pass  from 
the  prevertebral  chain  of  ganglia  and  from  the  cerebro-spinal  nerves  to  these 
plexuses.  3,  Various  ganglia  and  plexuses  in  the  substance  of  many  of  the 
viscera,  as  in    the   stomach,  intestines,  and    urinary  bladder.     These,  which 


Gray  Ramus 
White  Ramus 

Sympathetic  Gang  1 1  on. 


Recurrent  Branc 

of  Meninges 


Sympathetic  Ganglion. 


Fig.   418. — Schematic  Representation  of  the  Relation  of  the  Constituents  of  the  Sympathetic 
Chain  and  the  Spinal  Nerve.       (Modified  from  Hardesty,  in  Morris'  Anatomy.) 


are  for  the  most  part  microscopic,  also  freely  communicate  with  other  parts 
of  the  system,  as  well  as  with  the  cerebro-spinal  axis. 

The  connections  between  these  parts  are  as  follows:  1,  The  visceral 
branch  or  white  ramus,  of  certain  spinal  nerves,  which  passes  into  the  lateral 
chain.  2,  The  gray  rami  consist  of  bundles  of  fibers,  usually  non-medullated, 
which  pass  from  the  chain  ganglia  back  into  the  spinal  or  cranial  nerves,  the 


ORGANIZATION     AM)     DISTRIBUTION 


m 


fibers  of  which  they  accompany  to  the  periphery.  3,  From  this  chain  the 
rami  efferentes  pass  into  the  collateral  ganglia,  and  from  these  again  other 
branches  pass  off  into  the  organs,  to  end  in  the  terminal  ganglia. 

The  white  rami  are  absent  in  all  the  spinal  nerves  in  the  regions  above 
the  second  (occasionally  the  first)  thoracic  nerve  root,  and  below  the  second 


Fig.  419. — Scheme  of  the  Constitution  and  Connections  of  Gangliated  Cord  of  the  Sympathetic. 
The  gangliated  cord  is  indicated  on  the  right,  with  the  arrangement  of  the  fibers  arising  from 
ganglion  cells.  On  the  left,  the  roots  and  trunks  of  the  spinal  nerves  are  shown,  with  the  arrange- 
ment of  the  white  ramus  communicans  above  and  the  gray  ramus  below.  The  cells  of  origin  in 
the  ventral  cord  of  the  fibers  constituting  the  white  ramus  are  not  shown.      (Cunningham.) 


lumbar  nerve  root,  with  the  occasional  exception  of  the  roots  of  the  third  and 
fourth  lumbar  nerves.  This  is  a  rather  restricted  field  of  origin  for  the  pregan- 
glionic libers  which  compose  the  white  rami.  These  fibers  end  in  adjacent 
ganglia  of  the  chain,  or  pass  to  higher  or  lower  levels  or  to  more  peripheral 
ganglia. 

A  peculiarity  in  the  structure  of  these  white  medullated  visceral  nerves  is  the 
38 


594  THE     NERVOUS    SYSTEM 

fineness  of  their  fibers.  They  are  a  third  or  a  fourth  of  the  diameter  of  ordinary 
medullated  fibers,  measuring  c.8  p.  to  2.7//  instead  of  14  ;j.  to  19  /1.  Such 
fibers  are  a  peculiarity  of  the  spinal  nerve  roots  chiefly  in  the  thoracic  region, 
but  also  found  in  the  second  and  third  sacral  nerves,  and  constitute  there 
the  nervi  erigentes  which  pass  directly  to  the  hypogastric  plexus.  From  the 
hypogastric  plexus  branches  pass  upward  into  the  inferior  mesenteric  ganglia 
and  downward  to  the  bladder,  rectum,  and  generative  organs.  These  nerves, 
called  by  Gaskell  pelvic  splanchnic  nerves,  differ  from  the  rami  viscerales  of 
the  thoracic  region  only  in  not  communicating  with  the  lateral  ganglia;  the 
branches  which  pass  upward  from  the  thoracic  region  to  the  neck,  he  calls 
cervical  splanchnics,  and  the  splanchnics  proper  abdominal  splanchnics. 

Functions.  The  researches  of  Gaskell  and  of  Langley  have  done 
much  to  clear  up  the  former  confusion  as  to  the  distribution  and  functions 
of  the  sympathetic.  The  sympathetic  nerve  fibers  are  distributed  to  smooth 
muscle,  to  gland  cells,  and  to  cardiac  muscle.  These  are  all  organs  which 
carry  on  their  activities  either  automatically  or  reflexly.  There  is  no  volun- 
tary control  of  the  function  of  these  organs. 

The  efferent  sympathetic  fibers  supply  the  muscles  of  the  vascular  system,  to 
which  they  send  the  vaso-motor  fibers,  i.e.,  vaso-constrictor  and  cardiac  aug- 
mentor  or  accelerator;  and  vaso-inhibitory  fibers,  i.e.,  vaso-dilators.  They 
supply  the  muscles  of  the  alimentary  canal  and  of  the  urinogenital  system. 
The  details  of  arrangement  and  functional  control  of  these  complex  systems 
have  already  been  discussed  in  connection  with  the  function  of  the  organ  or 
part  concerned.     They  supply  the  salivary,  gastric,  and  pancreatic  glands. 

According  to  Gaskell  the  functions  of  the  main  sympathetic  ganglia  are  the 
following:  1,  They  effect  the  conversion  of  medullated  into  non-medullated 
fibers.  2,  They  possess  a  nutritive  influence  over  the  nerves  which  pass  from 
them  to  the  periphery.     3,  They  increase  the  number  of  fibers. 

The  sympathetic  ganglia  are  not  nerve  centers  in  the  usual  sense.  It  is 
better  to  regard  them  merely  as  distributing  organs  in  which  reflexes  of  central 
origin  and  comparatively  simple  type  are  distributed  over  relatively  large 
areas.  These  ganglia  do  not  possess  the  power  of  reflex  function.  A  type 
of  pseudo-reflex  has  been  described  depending  on  the  law  of  neurone  reaction. 
But  it  is  not  supposed  that  such  reflexes  occur  in  the  normal  animal. 

Afferent  or  sensory  fibers  of  the  ordinary  spinal-root  ganglion  cells  are 
present  in  the  sympathetic  nerves  of  the  splanchnic  region,  being  distributed 
merely  to  the  visceral  region.  True  afferent  sympathetic  fibers  have  been 
demonstrated.  These  arise  from  cells  located  in  the  sympathetic  ganglia,  and 
pass  through  the  rami  communicantes,  to  end  by  terminal  arborizations  in  the 
spinal  ganglia,  chiefly  around  cells  of  the  Dogiel  type.  The  number  and 
significance  of  these  afferent  neurones  are  yet  uncertain. 


CHAPTER   XV 

THE  SENSES 

Through  the  medium  of  the  nervous  system  man  obtains  a  knowledge 
of  the  existence  both  of  the  various  parts  of  his  body  and  of  the  external 
world.  This  knowledge  is  based  upon  sensations  resulting  from  the  stimula- 
tion of  certain  centers  in  the  brain  by  nerve  impulses  conveyed  to  them  by 
afferent  nerves.  Under  normal  circumstances  the  following  structures  are 
necessary  for  sensation:  a,  A  peripheral  organ  for  the  reception  of  the  im- 
pression; b,  a  nerve  for  conducting  it;  c,  a  nerve  center  for  feeling  or  per- 
ceiving it. 

Sensations  may  be  conveniently  classed  as,  i,  common,  and  2,  special 
sensations. 

Common  Sensations.  Under  this  head  fall  all  those  general  sen- 
sations which  cannot  be  distinctly  localized  in  any  particular  part  of  the  body, 
such  as  fatigue,  discomfort,  faintness,  satiety,  nausea,  together  with  hunger 
and  thirst,  in  which,  in  addition  to  a  general  discomfort,  there  is  in  many 
persons  a  distinct  sensation  referred  to  the  stomach  or  fauces.  In  this  class 
must  also  be  placed  the  various  stimulations  of  the  mucous  membrane  of 
the  bronchi,  which  give  rise  to  coughing,  and  also  the  sensations  derived  from 
various  viscera,  such  as  the  desire  to  defecate,  to  urinate,  and  in  the  female 
the  sensations  which  precede  the  expulsion  of  the  fetus.  It  is  impossible  to 
draw  a  very  clear  line  of  demarcation  between  many  of  the  common  sensa- 
tions above  mentioned  and  the  sense  of  touch,  which  forms  the  connecting 
link  between  the  general  and  special  sensations.  Touch  is  classed  with  the 
special  senses,  and  will  be  considered  in  the  same  group  with  them;  yet  it 
differs  from  them  in  its  wide  distribution  over  the  body.  Among  common 
sensations  some  would  rank  the  muscle  sense,  which  has  been  already 
alluded  to.  It  is  by  means  of  this  sense  that  we  become  aware  of  the  con- 
dition of  the  muscles,  and  thus  obtain  the  information  necessary  for  their 
adjustment  to  various  purposes — standing,  walking,  grasping,  etc.  This 
muscular  sensibility  is  shown  in  our  power  to  estimate  the  differences  between 
weights  by  the  different  muscular  efforts  necessary  to  raise  them.  It  must 
be  carefully  distinguished  from  the  sense  of  contact  and  of  pressure,  of  which 
the  skin  is  the  organ.  When  standing  erect,  we  can  feel  the  ground  contact, 
and  there  is  a  sense  of  pressure,  due  to  our  feet  being  pressed  against  the 
ground  by  the  weight  of  the  body.  Both  these  are  derived  from  the  skin 
of  the  sole  of  the  foot.     If  now  we  raise  the  body  on  the  toes,  we  are  con- 

595 


596  THE    SENSES 

scious,  through  the  muscular  sense,  of  a  muscular  effort  made  by  the  muscles 
of  the  calf.     But  the  muscle  sense  will  be  discussed  further,  page  603. 

Special  Sensations.  The  special  senses  include  Touch,  Temper- 
ature (Heat  and  Cold),  Taste,  Smell,  Hearing,  Sight. 

The  most  important  distinction  between  common  and  special  sensations 
is  that  by  the  former  we  are  made  aware  of  certain  conditions  of  various 
parts  of  our  bodies,  while  from  the  latter  is  gained  a  knowledge  of  the  ex- 
ternal world.  This  difference  will  be  clear  if  we  compare  the  sensations  of 
pain  and  touch,  the  former  of  which  is  a  common,  the  latter  a  special,  sensa- 
tion. "  If  we  place  the  edge  of  a  sharp  knife  on  the  skin,  we  feel  the  edge 
by  means  of  our  sense  of  touch;  we  perceive  a  sensation,  and  refer  it  to  the 
object  which  has  caused  it.  But  as  soon  as  we  cut  the  skin  with  the  knife, 
we  feel  pain,  a  feeling  which  we  no  longer  refer  to  the  cutting  knife,  but  which 
we  feel  within  ourselves,  and  which  communicates  to  us  the  fact  of  a  change 
of  condition  in  our  own  body.  By  the  sensation  of  pain  we  are  neither  able 
to  recognize  the  object  which  caused  it  nor  its  nature." 

It  is  important  in  studying  the  phenomena  of  sensation  clearly  to  under- 
stand that  the  sensorium,  or  seat  of  sensation,  is  in  the  brain,  and  not  in  the 
particular  organ  through  which  the  sensory  impression  is  received.  In  com- 
mon parlance  we  are  said  to  see  with  the  eye,  hear  with  the  ear,  etc.,  but  in 
reality  these  organs  are  only  adapted  to  receive  stimuli  which  produce  changes 
that  are,  through  their  respective  nerves,  conducted  to  the  sensorium,  to  give 
rise  to  sensation. 

Hence,  if  the  optic  nerve  is  severed,  vision  is  no  longer  possible.  Although 
the  image  falls  on  the  retina  as  before,  the  sensory  impulse  can  no  longer  be 
conveyed  to  the  sensorium.  When  any  given  sensation  is  felt,  all  that  we 
can  with  certainty  affirm  is  that  some  part  of  the  brain  is  excited.  The  ex- 
citing cause  may  be  some  object  of  the  external  world,  producing  an  objective 
sensation;  or  the  condition  of  the  sensorium  may  be  due  to  some  excitement 
within  the  brain  itself,  in  which  case  the  sensation  is  termed  subjective.  The 
mind  habitually  refers  sensations  to  external  causes;  and  hence,  whenever 
they  are  subjective  we  can  hardly  divest  ourselves  of  the  idea  of  an  external 
cause,  and  an  illusion  is  the  result. 

Sensory  Illusions.  Numberless  examples  of  such  illusions  might 
be  quoted.  As  familiar  cases  may  be  mentioned,  humming  and  buzzing  in 
the  ears  caused  by  some  irritation  of  the  auditory  nerve  or  center.  These 
stimuli  may  even  be  interpreted  as  musical  sounds,  or  voices,  sometimes 
termed  auditory  spectra.  So-called  optical  illusions  in  which  objects  are 
described  as  seen,  although  not  present,  may  be  caused  by  changes  going 
on  in  some  part  of  the  visual  apparatus  beyond  the  eye.  Such  illusions  are 
most  strikingly  exemplified  in  cases  of  delirium  tremens  or  other  forms  of 
delirium,  and  may  take  the  form  of  animals  such  as  cats,  rats,  or  creeping 
loathsome  forms,  etc. 


SENSE    PERCEPTIONS  597 

One  uniform  internal  cause,  which  may  act  on  all  the  nerves  of  the  senses 
in  the  same  manner,  is  capillary  congestion.  This  one  cause  excites  in  the 
retina,  while  the  eyes  are  closed,  the  sensations  of  light  and  luminous  flashes; 
in  the  auditory  nerve,  the  sensation  of  humming  and  ringing  sounds;  in  the 
olfactory  nerve,  the  sense  of  odors;  and  in  the  nerves  of  feeling,  the  sensation 
of  pain.  In  the  same  way  a  chemical  substance  introduced  into  the  blood 
may  excite  in  the  nerves  of  each  sense  peculiar  symptoms:  In  the  optic  nerves, 
the  appearance  of  luminous  sparks  before  the  eyes;  in  the  auditory  nerves, 
tinnitus  aurium;  and  in  the  common  sensory  nerves,  the  sensations  of  creeping 
over  the  surface.  So,  also,  among  external  causes,  the  stimulus  of  electricity, 
or  the  mechanical  influence  of  a  blow,  concussion,  or  pressure,  excites  in  the 
eye  the  sensation  of  light  and  colors;  in  the  ear,  a  sense  of  a  loud  sound  or 
of  ringing;  and  in  the  tongue,  a  saline  or  acid  taste. 

Sense  Perceptions.  The  habit  of  constantly  referring  our  sensa- 
tions to  external  causes  leads  us  to  interpret  the  various  modifications  which 
external  objects  produce  in  our  sensations,  as  properties  of  the  external  bodies 
themselves.  Thus  we  speak  of  certain  substances  as  possessing  a  disagreeable 
taste  and  smell;  whereas,  the  fact  is  their  taste  and  smell  are  only  disagree- 
able to  us.  It  is  evident,  however,  that  on  this  habit  of  referring  our  sensa- 
tions to  causes  outside  ourselves,  perception,  depends  the  reality  of  the  ex- 
ternal world  to  us;  and  more  especially  is  this  the  case  with  the  senses  of 
touch  and  sight.  By  the  cooperation  of  these  two  senses,  aided  by  the  others, 
we  are  enabled  gradually  to  attain  a  knowledge  of  external  objects  which 
daily  experience  confirms,  until  we  come  to  place  unbounded  confidence  in 
what  is  termed  the  evidence  of  the  senses. 

We  must  draw  a  distinction  between  mere  sensations,  and  the  judgments 
based,  often  unconsciously,  upon  them.  Thus,  in  looking  at  a  near  object, 
we  unconsciously  estimate  its  distance  and  say  it  seems  to  be  ten  or  twelve 
feet  off.  But  the  estimate  of  its  distance  is  in  reality  a  judgment  based  on 
many  things  besides  the  appearance  of  the  object  itself;  among  which  may 
be  mentioned  the  number  of  intervening  objects,  the  number  of  steps  which 
from  past  experience  we  know  we  must  take  before  we  could  touch  it,  and 
many  others. 

I.  THE  SENSES  OF  TOUCH,  PAIN,  TEMPERATURE,  AND 
THE  MUSCLE  SENSE. 

The  Sense  of  Touch.  The  sense  of  touch,  like  all  the  special 
senses,  possesses  a  special  end-organ  for  the  initiation  of  a  nerve  impulse 
through  contact  with  external  objects.  The  sense  organ  of  touch  is  not  con- 
fined to  particular  parts  of  the  body  of  small  extent,  like  the  organ  of  sight, 
for  example,  but  is  found  in  all  parts  of  the  skin  and  its  inversions,  the  stomo- 
deum  and  proctodeum.     The  nerves  of  sensation  are  contained  in  the  same 


.508 


THE     SENSES 


trunks  with  other  sensory  nerves.  They  are  found  in  the  posterior  or  sen- 
sory roots  of  the  spinal  nerves  and  in  the  sensory  divisions  of  the  cranial 
nerves,  especially  the  fifth,  seventh,  ninth,  and  tenth. 

All  parts  of  the  epidermis  supplied  with  sensory  nerves  are  thus,  in  some 
degree,  organs  of  touch,  yet  the  sense  is  exercised  in  greatest  perfection  in 
certain  parts,  the  sensibility  of  which  is  extremely  delicate,  e.g.,  the  skin  of 
the  hands,  the  tongue,  and  the  lips,  which  are  provided  with  abundant  touch 
papilla?.  A  peculiar  and  very  acute  sense  of  touch  is  exercised  through  the 
medium  of  the  nails  and  teeth,  and,  to  a  less  extent,  the  hair  may  be  consid- 
ered an  organ  of  touch,  as  in  the  case  of  the  eyelashes. 

The  sense  of  touch  renders  us  conscious  of  the  presence  of  a  contact 
stimulus,  from  the  slightest  to  the  most  intense  degree  of  its  action.     The 


modifications  of  this  sense  often  depend  on  the  extent  of  the  parts  affected. 
The  sensation  of  pricking,  for  example,  is  produced  when  the  sensitive  fibers 
are  intensely  affected  in  a  small  extent;  the  sensation  of  pressure  indicates 
a  slighter  affection  of  the  parts  over  a  greater  extent  and  depth.  It  is  by  the 
depth  to  which  the  parts  are  affected  that  the  feeling  of  pressure  is  dis- 
tinguished from  that  of  mere  contact. 

In  almost  all  parts  of  the  body  which  have  delicate  tactile  sensibility  the 
epidermis,  immediately  over  the  dermal  papillae,  is  moderately  thin.  When 
its  thickness  is  much  increased,  as  over  the  heel,  the  sense  of  touch  is  very 
much  dulled.  On  the  other  hand,  when  it  is  altogether  removed,  and  the 
cutis  laid  bare,  the  sensation  of  contact  is  replaced  by  one  of  pain.  Further, 
in  all  highly  sensitive  parts,  the  papillae  are  numerous  and  highly  vascular, 
and  the  sensory  nerves  are  connected  with  special  end-organs  which  have 
been  described  on  page  72  et  seq. 


ACUTENESS     OF    THE    SENSE  599 

The  special  endings  of  the  nerves  which  have  to  do  with  touch  may,  how- 
ever, be  here  again  mentioned.  They  are  of  two  kinds,  viz.,  i,  Touch  cor- 
puscles, which  are  found  chiefly  in  the  hands  and  feet,  particularly  on  the 
palmar  surface  of  the  hands  and  fingers,  but  also  on  the  under  surface  of  the 
forearm,  on  the  nipple,  eyelids,  lips,  and  the  genital  organs.  Touch  corpuscles 
are  situated  in  the  cutis  vera.  2,  End  bulbs  axe  found  in  the  conjunctiva  and 
other  mucous  membranes,  the  lips,  genital  organs,  tongue,  rectum,  and  else- 
where, but  not  in  the  skin  proper.  As  regards  the  Pacinian  corpuscles  and 
similar  end-organs,  which  are  so  widely  distributed,  and  which  maybe  in  some 
way  connected  with  the  sensation,  when  they  are  found  in  the  skin  they  are  situ- 
ated very  deeply  in  the  cutis  vera  or  in  the  subcutaneous  tissue.  They  are 
extremely  numerous  on  the  nerves  of  the  palmar  surface  of  the  fingers.  In 
addition  to  these  special  nerve  endings,  nerve  fibers  terminate  everywhere  in 
the  skin  between  the  cells  of  the  Malpighian  stratum  of  the  epidermis. 

The  acuteness  of  the  sense  of  touch  depends  very  largely  on  the  cutaneous 
circulation,  which  is  of  course  greatly  influenced  by  external  temperature. 
Hence  the  numbness,  familiar  to  every  one,  produced  by  the  application  of 
cold  to  the  skin. 

Acuteness  of  the  Sense.  The  perfection  of  the  sense  of  touch  on 
different  parts  of  the  surface  is  proportioned  to  the  minimal  pressure  re- 
quired to  stimulate  the  point,  i.e.,  the  threshold  stimulus.  Or  it  can  be 
measured  by  the  power  which  such  parts  possess  of  distinguishing  and  isolat- 
ing the  sensations  produced  by  two  points  placed  close  together.  This  latter 
is  a  measure  of  the  power  of  localization  in  a  degree.  This  power  depends, 
at  least  in  part,  on  the  number  of  primitive  nerve  fibers;  for  the  fewer  the 
primitive  fibers  which  an  organ  receives,  the  more  likely  is  it  that  several 
impressions  on  different  contiguous  points  will  act  on  only  one  nervous  fiber, 
and  hence  be  confounded,  and  perhaps  produce  but  one  sensation.  Experi- 
ments have  been  made  to  determine  the  tactile  properties  of  different  parts 
of  the  skin,  as  measured  by  this  power  of  distinguishing  distances  between 
points  of  simultaneous  contact.  These  consist  in  touching  the  skin  with  the 
points  of  a  pair  of  compasses  sheathed  with  cork,  and  in  ascertaining  how 
close  the  points  of  the  compasses  might  be  brought  to  each  other  and  still 
be  felt  as  two  bodies. 

Table  of    Variations  in  the  Tactile  Sensibility  of  the  Different  Parts   of 

the  Skin. 

The  measurement  indicates  the  least  distance  at  which  the  two  blunted  points  of  a  pair 
of  compasses  could  be  separately  distinguished.     (E.  H.  Weber.) 

Tip  of  tongue,       ...........  1  mm. 

Palmar  surface  of  third  phalanx  of  forefinger,            .....  2  " 

Palmar  surface  of  second  phalanges  of  fingers,           .....  4  " 

Red  surface  of  under-lip,        .........  4  " 

Tip  of  nose, 6  " 

Middle  of  dorsum  of  tongue,            ........  8 


GOO  TI1K     SENSES 

Palm  of  hand, i°  mm. 

Center  of  hard  palate,    ..........12 

Dorsal  surface  of  first  phalanges  of  fingers,       ......  14 

Back  of  hand, 25     " 

Dorsum  of  foot  near  toes,        .........  37 

Gluteal  region,        ...........  37 

Sacral  region,  ...........  37 

Upper  and  lower  parts  of  forearm,  .  .  -  -  -  •  .  -  37 

Back  of  neck  near  occiput,      .........  50 

Upper  dorsal  and  mid-lumbar  regions,      .......  50 

Middle  part  of  forearm, 62     " 

Middle  of  thigh, 62 

Mid-cervical  region,  ..........  62 

Mid-dorsal  region,  ..........  62 

In  the  case  of  the  limbs,  before  the  points  are  recognized  as  two,  they 
have  to  be  further  separated  when  the  line  joining  them  is  in  the  long  axis  of 
the  limb  than  when  in  the  transverse  direction. 

According  to  Weber  the  mind  estimates  the  distance  between  two  points 
by  the  number  of  unexcited  nerve  endings  which  intervene  between  the  two 
points  touched.  It  would  appear  that  a  certain  number  of  intervening  un- 
excited nerve  endings  is  necessary  before  two  points  touched  can  be  recognized 
as  separate,  and  the  greater  this  number  the  more  clearly  are  the  points  of 
contact  distinguished  as  separate.  The  delicacy  of  the  sense  of  touch  may 
be  very  much  increased  by  practice.  A  familiar  illustration  occurs  in  the 
case  of  the  blind,  who,  by  constant  practice,  can  acquire  the  power  of  reading 
raised  letters  the  forms  of  which  are  almost,  if  not  quite,  undistinguishable  by 
the  sense  of  touch  to  an  ordinary  person. 

The  different  degrees  of  sensitiveness  possessed  by  different  parts  may 
give  rise  to  errors  of  judgment  in  estimating  the  distance  between  two  points 
where  the  skin  is  touched.  Thus,  if  blunted  points  of  a  pair  of  compasses 
(maintained  at  a  constant  distance  apart)  be  slowly  drawn  over  the  skin  of 
the  cheek  toward  the  lips,  it  is  almost  impossible  to  resist  the  conclusion  that 
the  distance  between  the  points  is  gradually  increasing.  When  they  reach 
the  lips  they  seem  to  be  considerably  farther  apart  than  on  the  cheek.  Thus, 
too,  our  estimate  of  the  size  of  a  cavity  in  a  tooth  is  usually  exaggerated  when 
based  upon  sensations  derived  from  the  tongue  alone.  Another  curious 
illusion  may  here  be  mentioned.  If  we  close  the  eyes,  and  place  a  small 
marble  or  pea  between  the  crossed  fore  and  middle  fingers,  we  seem  to  be 
touching  two  marbles,  figure  480.  This  illusion  is  due  to  an  error  of  judg- 
ment. The  marble  is  touched  by  two  surfaces  which,  under  ordinary  cir- 
cumstances, could  be  touched  only  by  two  separate  marbles,  hence  the  mind, 
taking  no  cognizance  of  the  fact  that  the  fingers  are  crossed,  forms  the  con- 
clusion that  two  sensations  are  due  to  two  marbles. 

Sense  of  Temperature.      The  whole  surface  of  the  body  is  more  or 
less  sensitive  to  differences  of  temperature.     The  sensation  of  heat  is  distinct 


SENSE     OF     TEMPERATURE 


001 


from  that  of  touch,  hence  it  would  seem  reasonable  to  suppose  that  there  are 
special  nerves  and  nerve  endings  for  temperature.  At  any  rate  the  power  of 
discriminating  temperature  may  remain  unimpaired  when  the  sense  of  touch 
is  temporarily  in  abeyance.  Thus  if  the  ulnar  nerve  be  compressed  at  the 
elbow  till  the  sense  of  touch  is  very  much  dulled  in  the  fingers  which  it  sup- 
plies, the  sense  of  temperature  remains  quite  unaffected.  And  in  certain 
diseases  of  the  cord  the  sense  of  touch  may  be  impaired  in  a  part,  and  tem- 
perature remain  undisturbed,  or  the  converse. 

The  mapping  of  the  surface  of  a  part  of  the  skin  with  reference  to  its 
sensibility  to  temperature  reveals  the  fact  that  there  are  definite  heat  and 


Fig.  421. — Diagram  of  a  Part  of  the  Hand,  Showing  Distribution  of  Sense  Spots:  for  touch.  A; 
for  heat,  B;  and  for  cold,  C.  In  A  the  skin  is  sensitive  except  at  the  parts  marked  with  black; 
in  B  and  C,  the  intensity  of  the  shading  represents  the  relative  sensitiveness.      (Goldscheider.) 


cold  spots.  Furthermore,  the  areas  do  not  coincide,  leading  us  to  conclude 
that  there  are  two  distinct  sense  organs  concerned,  figure  421,-  B  and  C. 

The  sensations  of  heat  and  cold  are  often  exceedingly  fallacious,  and  in 
many  cases  are  no  guide  at  all  to  the  absolute  temperature  as  indicated  by 
a  thermometer.  All  that  we  can  with  safety  infer  from  our  sensations  of 
temperature  is  that  a  given  object  is  warmer  or  cooler  than  the  skin.  Thus 
the  temperature  of  our  skin  is  the  standard;  and  as  this  varies  from  hour  to 
hour  according  to  the  activity  of  the  cutaneous  circulation,  our  estimate  of 
the  absolute  temperature  of  any  body  must  necessarily  vary  too.  If  we  put 
the  left  hand  into  water  at  50  C.  (400  F.)  and  the  right  into  water  at  450  C. 
(no°  F.),  and  then  immerse  both  in  water  at  270  C.  (8o°  F.),  it  will  feel  warm 
to  the  left  hand,  but  cool  to  the  right.  Again,  a  piece  of  metal  which  has 
really  the  same  temperature  as  a  given  piece  of  wood  will  feel  much  colder, 
since  it  conducts  away  the  heat  much  more  rapidly.  For  the  same  reason 
air  in  motion  feels  very  much  cooler  than  air  of  the  same  temperature  at  rest. 

In  some  cases  we  are  able  to  form  a  fairly  accurate  estimate  of  absolute 
temperature.  Thus,  by  plunging  the  elbow  into  a  bath,  a  practised  bath- 
attendant  can  tell  the  temperature  sometimes  within  half  a  degree  centigrade. 

The  temperatures  which  cm  be  readily  discriminated  are  between  io°  and 


602  THE     SENSES 

450  C.  (500  and  1150  F.);  very  low  and  very  high  temperatures  alike  produce  a 
burning  sensation.  A  temperature  appears  higher  according  to  the  extent  of 
cutaneous  surface  exposed  to  it.  Thus,  water  of  a  temperature  which  can  be 
readily  borne  by  the  hand  is  quite  intolerable  if  the  whole  body  be  immersed. 

The  delicacy  of  the  sense  of  temperature  coincides  in  the  main  with  that 
of  touch,  and  appears  to  depend  largely  on  the  thickness  of  the  skin;  hence, 
in  the  elbow,  where  the  skin  is  thin,  the  sense  of  temperature  is  delicate, 
though  that  of  touch  is  not  remarkably  so.  Weber  has  further  ascertained 
the  following  facts:  two  points  so  near  together  on  the  skin  that  they 
produce  but  a  single  impression,  at  once  give  rise  to  tivo  sensations,  when 
one  is  hotter  than  the  other.  Moreover,  of  two  bodies  of  equal  weight,  that 
which  is  the  colder  feels  heavier  than  the  other. 

As  every  sensation  is  attended  with  a  perception  and  leaves  behind  it  an 
idea  in  the  mind  which  can  be  reproduced  at  will,  we  are  enabled  to  compare 
the  idea  of  a  past  sensation  with  another  sensation  really  present.  Thus  we 
can  compare  the  weight  of  one  body  with  another  which  we  had  previously 
felt,  of  which  the  idea  is  retained  in  our  mind.  Weber  was  indeed  able  to 
distinguish  in  this  manner  between  temperatures  experienced  one  after 
the  other,  better  than  between  temperatures  to  which  the  two  hands  were 
simultaneously  subjected.  This  power  of  comparing  present  with  past  sensa- 
tions diminishes,  however,  in  proportion  to  the  time  which  has  elapsed  between 
them.  After-sensations  left  by  impressions  on  nerves  of  common  sensibility 
or  touch  are  very  vivid  and  durable.  As  long  as  the  condition  into  which 
the  stimulus  has  thrown  the  organ  endures,  the  sensation  also  remains,  though 
the  exciting  cause  should  have  long  ceased  to  act.  Both  painful  and  pleasur- 
able sensations  afford  many  examples  of  this  fact. 

Sense  of  Pain.  As  regards  painful  sensations,  three  views  can  be 
taken:  1,  That  it  is  a  special  sensation  provided  with  a  special  conducting 
apparatus  in  each  part  of  the  body;  2,  that  it  is  produced  by  an  over-stimula- 
tion of  the  special  nerves  concerned  with  touch  or  temperature,  or  of  the 
other  nerves  of  special  sense;  or  3,  that  it  is  an  over-stimulation  of  the  nerves 
of  common  sensation,  which  tell  us  of  the  condition  of  our  own  bodies,  both 
of  the  surface  and  also  of  the  internal  organs.  There  seems  to  be  much  in 
favor  of  all  of  these  views.  The  weight  of  evidence  is,  however,  rather  against 
there  being  any  special  pain  sense  with  a  special  end-organ  and  fibers,  though 
Barker  in  his  own  arm  experienced  the  presence  of  pain  sensations  while 
there  was  absence  of  sensations  of  touch  and  temperature.  It  is,  indeed, 
certain  that,  even  if  any  variety  of  pain  be  a  special  sensation,  some  kind  of 
pain  may  be  produced  by  stimulation  of  the  bare  sensory  nerves  apart  from 
any  special  form  of  nerve  termination.  It  is  said  that  the  main  difference 
between  the  common  sensory  apparatus  which  tells  us  of  the  condition  of  all 
parts  of  the  body  of  which  thirst  and  hunger  are  but  examples,  and  the 
special  sense  of  touch  and  temperature,  is  that  the  latter  are  provided  with 


THE    MUSCULAR    SENSE  603 

a  special  local  apparatus.  By  means  of  this  apparatus  we  are  able  to  local- 
ize the  sensation.  Such  a  special  apparatus  is  evidently  not  absolutely  es- 
sential for  the  sensation  of  pain,  but  this  does  not  exclude  the  idea  that  pain 
may  result  from  over-stimulation  of  a  nerve  of  special  sense  or  of  its  termina- 
tion. 

The  Muscular  Sense.  The  estimate  of  a  weight  is  usually  based 
on  two  sensations:  i,  of  pressure  on  the  skin,  and  2,  the  sense  of  muscular 
resistance. 

The  estimate  of  weight  derived  from  a  combination  of  these  two  sensations 
(as  in  lifting  a  weight)  is  more  accurate  than  that  derived  from  the  former 
alone  (as  when  a  weight  is  laid  on  the  hand);  thus  Weber  found  that  by  the 
former  method  he  could  generally  distinguish  io|  oz.  from  20  oz.,  but  not 
19I  oz.  from  20,  while  by  the  latter  he  could  at  most  distinguish  only  14 \  oz. 
from  15  oz. 

It  is  not  the  absolute,  but  the  relative,  amount  of  the  difference  of  weight 
which  we  have  thus  the  faculty  of  perceiving. 

It  is  not,  however,  certain,  that  our  idea  of  the  amount  of  muscular  force 
used  is  derived  solely  from  the  muscular  sense.  We  have  the  power  of  esti- 
mating very  accurately  beforehand,  and  of  regulating,  the  amount  of  nervous 
influence  necessary  for  the  production  of  a  certain  degree  of  movement. 
When  we  lift  a  vessel,  with  the  contents  of  which  we  are  not  acquainted,  the 
force  we  employ  is  determined  by  the  idea  we  have  conceived  of  its  weight. 
If  it  should  happen  to  contain  some  very  heavy  substance,  as  quicksilver, 
we  shall  probably  fail  in  the  attempt;  the  amount  of  muscular  action,  or  of 
nervous  energy,  which  we  had  exerted  being  insufficient.  It  is  possible  that 
in  the  same  way  the  idea  of  weight  and  pressure  in  raising  bodies,  or  in  resist- 
ing forces,  may  in  part  arise  from  a  consciousness  of  the  amount  of  nervous 
energy  transmitted  from  the  brain  rather  than  from  a  sensation  in  the  muscles 
themselves.  The  mental  conviction  of  the  inability  longer  to  support  a  weight 
must  also  be  distinguished  from  the  actual  sensation  of  fatigue  in  the  muscles. 

So,  with  regard  to  the  ideas  derived  from  sensations  of  touch  combined 
with  movements,  it  is  doubtful  how  far  the  consciousness  of  the  extent  of 
muscular  movement  is  obtained  from  sensations  in  the  muscles  themselves. 
The  sensation  of  movement  attending  the  motions  of  the  hand  is  very  slight; 
and  persons  who  do  not  know  that  the  action  of  particular  muscles  is  necessary 
for  the  production  of  given  movements,  do  not  suspect  that  the  movement 
of  the  fingers,  for  example,  depends  on  an  action  in  the  forearm.  The  mind 
has,  nevertheless,  a  very  definite  knowledge  of  the  changes  of  position  pro- 
duced by  movements;  and  it  is  on  this  that  the  ideas  which  it  conceives  of 
the  extension  and  form  of  a  body  are  in  great  measure  founded. 

There  is  no  marked  development  of  common  sensibility  to  be  made  out 
in  muscles:  they  may  be  cut  without  the  production  of  pain.  On  the  other 
hand,  there  is  no  doubt  that  afferent  impulses  must  pass  upward  from  muscles 


(J04  THE    SENSES 

and  tendons  acquainting  the  brain  with  their  condition.  This,  then,  must  be 
a  special  sense.  It  has  been  suggested  that  the  minute  end-bulbs  of  Golgi 
found  in  tendons,  and  that  the  Pacinian  corpuscles  in  the  neighborhood  of 
joints,  are  the  terminal  organs  of  this  special  sense. 

Judgment  of  the  Form  and  Size  of  Bodies.  By  the  sense  of  touch  the  mind 
is  made  acquainted  with  the  size,  form,  and  other  external  characters  of 
bodies.  And  in  order  that  these  characters  may  be  easily  ascertained,  the 
sense  of  touch  is  especially  developed  in  those  parts  which  can  be  readily 
moved  over  the  surface  of  bodies.  Touch,  in  its  more  limited  sense,  or  the 
act  of  examining  a  body  by  the  touch,  consists  merely  in  a  voluntary  employ- 
ment of  this  sense  combined  with  movement,  and  stands  in  the  same  relation 
to  the  sense  of  touch,  or  common  sensibility,  generally,  as  the  act  of  seeking, 
following,  or  examining  odors  does  to  the  sense  of  smell.  The  hand  is  the 
best  adapted  for  it,  by  reason  of  its  peculiarities  of  structure — namely,  its 
capability  of  pronation  and  supination,  which  enables  it,  by  the  movement 
of  rotation,  to  examine  the  whole  circumference  of  a  body;  the  power  it 
possesses  of  opposing  the  thumb  to  the  rest  of  the  hand,  and  the  relative 
mobility  of  the  fingers ;  and  lastly  from  the  abundance  of  the  sensory  terminal 
organs  which  it  possesses.  In  forming  a  conception  of  the  figure  and  extent 
of  a  surface,  the  mind  multiplies  the  size  of  the  hand  or  fingers  used  in  the 
inquiry  by  the  number  of  times  which  it  is  contained  in  the  surface  traversed; 
and,  by  repeating  this  process  with  regard  to  the  different  dimensions  of  a 
solid  body,  acquires  a  notion  of  its  cubical  extent,  but,  of  course,  only  an  im- 
perfect notion,  as  other  senses,  e.g.,  the  sight,  are  required  to  make  it  complete. 

It  is  impossible  in  this  consideration  to  say  how  much  of  our  knowledge 
of  the  thing  touched  depends  upon  pressure  and  how  much  upon  the  mus- 
cular sense. 

II.    TASTE  AND  SMELL. 

The  special  sense  organs  for  taste  and  smell  are  stimulated  by  chemical 
substances,  the  former  by  chemicals  in  solution,  the  latter  by  volatile  materials. 
They  are  also  closely  associated  in  action  and  we  do  not  always  differentiate 
between  the  two. 

THE  SENSE  OF  TASTE. 

The  conditions  for  the  perceptions  of  taste  are:  i,  the  presence  of  a  sense 
organ,  a  nerve,  and  a  nerve  center  with  special  endowments;  2,  the  excitation 
of  the  sense  organ  by  the  sapid  matters,  which  for  this  purpose  must  be  in  a 
state  of  solution;   3,  a  temperature  of  about  370  to  400  C.  (980  to  ioo°  F.). 

The  Nerves  and  Organs  of  Taste.  The  principal  organ  of  the  sense 
of  taste  is  the  tongue.      But  the  soft  palate  and  its  arches,  the  uvula,  Umsils, 


THE  NEHYES  AND  ORGANS  OF  TASTE 


605 


and  probably  the  upper  part  of  the  pharynx,  are  also  endowed  with  taste. 
These  parts,  together  with  the  base  and  posterior  parts  of  the  tongue,  are 
supplied  with  branches  of  the  glosso-pharyngeal  nerve,  and  evidence  has 
been  already  adduced  that  this  is  the  principal  nerve  of  the  sense  of  taste. 
The  anterior  parts  of  the  tongue,  especially  the  edges  and  tip,  are  innervated 


Fig.  422. — Papillar  Surface  of  the  Tongue,  with  the  Fauces  and  Tonsils,  i,  Circumvallate 
papillae,  in  front  of  2,  the  foramen  cecum;  3,  fungiform  papillae;  4,  filiform  and  conical  papillae;  5, 
transverse  and  oblique  rugae;  6,  mucous  glands  at  the  base  of  the  tongue  and  in  the  fauces;  7, 
tonsils;  8.  part  of  the  epiglottis;  9,  median  glosso-epiglottidean  fold  (frenum  epiglottidis).  (From 
Sappey.) 


by  fibers  from  the  lingual  branch  of  the  fifth,  but  which  arise  in  the  ganglion 
of  the  pars  intermedia  and  are  distributed  in  the  chorda  tympani,  figures  387 
and  388. 

The  mucous  membrane  in  the  regions  just  mentioned  possesses  special 
epithelial  structures  called  taste  buds.     The  taste  buds  are  very  abundant 


006 


TFIK     SENSES 


in  the  side  walls  of  the  circumvallate  papilla-.  They  are  also  present  in  the 
fungiform  papillae,  in  the  foliate  papillae,  and  in  the  mucous  membrane. 
The  taste  bud  is  located  at  the  deeper  part  of  the  stratified  epithelium,  is 
ovoid  in  shape,  and  its  free  end.  abuts  on  the  surface  or  opens  to  the  surface 
by  a  short  canal.  It  is  composed  of  two  kinds  of  modified  epithelial  cells — 
the  supporting  cells,  which  are  long,  spindle-shaped  cells  that  form  a  sheath 
around  the  special  gustatory  cells;  and  the  taste  cells,  which  are  neuroepithe- 
lial cells  that  are  found  in  the  center  of  the  taste  bud.  They  are  very  slen- 
der cells  that  project  on  the  surface  by  a  delicate  process.  A  bundle  of  nerve 
fibrils  enters  the  base  of  each  taste  bud  and  forms  a  net  about  the  taste  cells. 
The  circumvallate,  the  fungiform,  and  the  filiform  papillae,  shown  in 
figure  422,  are  special  structures  that  facilitate  the  stimulation  of  the  taste 


Fig.  423. 


Fig.  424. 


Fig.  423. — Taste-Bud  from  Side  Wall  of  Circumvallate  Papillce.  (Merkel-Henle.)  a,  Taste- 
pore;  b,  nerve  fibers,  some  of  which  enter  the  taste  bud,  intrageminal  fibers,  while  others  end  freely 
in  the  surrounding  epithelium,  intergeminal  fibers. 

Fig.  424. — Vertical  Section  of  a  Circumvallate  Papilla  of  the  Calf.  1  and  3,  Epithelial  layers 
covering  it;  2,  taste  goblets;  4,  and  4',  duct  of  serous  gland  opening  out  into  the  pit  in  which  the 
papilla  is  situated;    5  and  6,  nerves  ramifying  within  the  papilla.      (Engelmann.) 


buds  by  sapid  substances.  They  are  all  formed  by  a  projection  of  the  mucous 
membrane,  and  contain  special  branches  of  blood-vessels  and  nerves.  In 
details  of  structure,  however,  they  differ  considerably  one  from  another. 

Circumvallate  Papillce.  These  papillae,  figure  424,  eight  or  ten  in  number, 
are  situated  in  two  V-shaped  lines  on  the  base  of  the  tongue.  They  are 
circular  elevations  from  1  to  2  mm.  in  diameter  each,  with  a  central  depres- 
sion, and  surrounded  by  a  circular  fissure,  at  the  outside  of  which  is  a 
slightly  elevated  ring.  Both  the  central  elevation  and  the  ring  are  formed 
of  close  set  simple  papillae. 

Fungiform  Papilla;.  The  fungiform  papillae  are  scattered  chiefly  over 
the  sides  and  tip,  and  sparingly  over  the  middle  of  the  dorsum,  of  the  tongue; 
the  name  is  deri  ed  from  their  being  usually  narrower  at  the  base  than  at 
the  summit.  They  also  are  supplied  with  loops  of  capillary  blood-vessels, 
and  nerve  fibers. 


TASTE    SENSATIONS  607 

Conical  or  Filiform  Papilloe.  These,  which  are  the  most  abundant 
papilla',  arc-  scattered  over  the  whole  surface  of  the  tongue,  but  especially 
over  the  middle  of  the  dorsum.  They  vary  in  shape  somewhat,  but  for  the 
most  part  are  conical. 

Taste  Sensations.  The  occurrence  of  two  kinds  of  special  sensi- 
bility, i.e.,  touch  and  taste  in  the  same  part,  makes  it  sometimes  difficult  to 
determine  whether  the  impression  produced  by  a  substance  is  perceived 
through  the  ordinary  tactile  sensitive  fibers,  or  through  those  of  the  sense  of 
taste.  In  many  cases,  indeed,  it  is  probable  that  both  sets  of  nerve  fibers 
are  concerned,  as  when  irritating  acrid  substances  are  introduced  into  the 
mouth. 

Many  of  the  so-called  tastes  are  due  to  the  sapid  substances  being  also 
odorous,  and  exciting  the  simultaneous  action  of  the  sense  of  smell.  This  is 
shown  by  the  insipid  tastes  of  certain  substances  when  their  action  on  the 
olfactory  nerves  is  prevented  by  closing  the  nostrils.  Many  of  the  popular 
drinks  lose  much  of  their  apparent  excellence  if  the  nostrils  are  held  close 
while  they  are  drunk. 

When  these  accessory  sensations  are  taken  into  account  it  is  found  that 
the  clearly  defined  tastes  are  reduced  to  four:  sweet,  bitter,  acid,  and  salt. 
These  taste  sensations  are  produced  by  the  respective  substances  when  in 
solution.  If  dry  salt  or  quinine  is  placed  on  the  surface  of  the  tongue,  no 
taste  appears  until  solution  takes  place  in  the  secretions  of  the  tongue.  A 
piece  of  metal,  as  a  silver  coin,  gives  rise  to  a  seemingly  distinct  taste  sensa- 
tion, called  metallic,  but  it  is  probably  not  to  be  accepted  as  coordinate  with 
the  others.  The  acid  taste  may  be  excited  by  electricity.  If  a  piece  of  zinc 
be  placed  beneath  and  a  piece  of  copper  above  the  tongue,  and  their  ends 
brought  into  contact,  an  acid  taste  (due  to  the  feeble  galvanic  current)  is 
produced.  The  delicacy  of  the  sense  of  taste  is  sufficient  to  discern  one  part 
of  sulphuric  acid  in  10,000  of  water,  or  one  part  of  quinine  in  200,000  of  water. 
But  it  is  far  surpassed  in  acuteness  by  the  sense  of  smell. 

ACUTENESS   OF   THE    SENSE    OF    TASTE.       (HALL.) 

The  average  of  10  individuals. 

Sugar 1  part  to  520 

Quinine 1      "     "  444,000 

Acetic  Acid 1     "     "  5,640 

Salt 1     "     "  469 

Exploration  of  the  taste  areas  reveals  the  fact  that  regions  of  the  tongue 
and  mouth  are  not  equally  sensitive  to  the  sapid  substances.  Sweet  tastes 
are  especially  developed  at  the  tip  and  sides  of  the  tongue,  while  bitter  tastes 
are  almost  absent  in  the  front,  but  especially  developed  on  the  basal  region, 
and  in  the  fauces  and  pharynx.     Salts  are  more  stimulating  to  the  tip  of  the 


008 


THE    SENSES 


tongue,  and  acids  along  the  sides.  Individual  tests  of  the  fungiform  papillae 
by  Oehrwall  showed  that  about  half  the  papillae  reacted  to  sweet,  bitter, 
and  acid,  but  that  certain  ones  reacted  only  to  sweet,  or  to  sweet  and  bitter, 
or  to  acid  and  bitter.  This  suggests  the  specific  nature  of  the  taste  sensa- 
tions and  tends  to  prove  that  there  may  be  a  special  organ  for  each  kind  of 
stimulus.  Experiments  have  also  shown  that  it  is  possible  to  do  away  with 
the  power  of  tasting  bitters  and  sweets  while  the  taste  for  acids  and  salts 
remains.  This  is  done  by  chewing  the  leaves  of  an  Indian  plant,  Gymnema 
sylvestre.  It  has  also  been  shown  that  the  power  of  tasting  sweet  substances 
disappears  before  that  of  tasting  bitter.  Other  experiments  have  shown  that 
the  mechanisms  for  salt  and  acid  tastes  are  distinct. 

After-tastes  and  Contrasts.     Very  distinct  sensations  of  taste  are 


Fig.  425. — Localization  of  Taste.     Bitter ;  acid ;  salt, ;  sweet - 

FC,  foramen  cecum;    CF,  circumvallate  papillae;    FP,  fungiform  papillae. 


— ;    T,  tonsils; 
(Hall.) 


frequently  left  after  the  substances  which  excited  them  have  ceased  to  act 
on  the  nerve,  as  the  after-taste  of  metallic  bitter,  which  remains  after  breaking 
the  stimulating  current.  Such  sensations  often  endure  for  a  long  time,  and 
modify  the  taste  of  other  substances  applied  to  the  tongue.  Thus,  the  taste 
of  sw^et  substances  is  intensified  after  the  tasting  of  common  salt.  After 
rinsing  the  mouth  with  water  containing  salt,  it  is  said  that  sweet  solutions 
are  perceived  that  are  too  dilute  to  be  detected  ordinarily.  Many  other 
chemicals  produce  similar  results.  The  application  of  a  sapid  substance, 
acid  for  example,  to  one  side  of  the  tongue  intensifies  the  sensation  produced 
by  a  sapid  substance  applied  to  the  other  side.  There  is  a  simultaneous  con- 
trast which  suggests  that  the  same  relation  exists  between  tastes  as  between 
colors,  of  which  those  that  are  opposed,  i.e.,  complementary,  render  each 


THE    SENSE     OF    SMELL  609 

other  more  vivid,  though  no  general  principles  governing  this  relation  have 
been  discovered  in  the  case  of  tastes.  In  the  art  of  cooking,  however,  atten- 
tion has  at  all  times  been  paid  to  the  consonance  or  harmony  of  flavors  in 
their  combination  or  order  of  succession,  just  as  in  painting  and  music  the 
fundamental  principles  of  harmony  have  been  employed  empirically  while 
the  theoretical  laws  were  unknown. 

Frequent  and  continued  repetitions  of  the  same  taste  render  the  perception 
of  it  less  and  less  distinct,  in  the  same  way  that  a  color  becomes  more  and 
more  dull  and  indistinct  the  longer  the  eye  is  fixed  upon  it.  There  is  fatigue 
of  the  taste  organ  at  some  point. 

THE  SENSE  OF  SMELL. 

The  sensation  of  smell  is  produced  by  the  action  of  odorous  particles  on  a 
special  end-apparatus,  which  in  turn  causes  nerve  impulses  that  arouse  changes 
in  a  special  area  in  the  sensorium.  The  stimulating  cause  is  the  direct  action 
of  chemical  substances  as  in  the  sense  of  taste.  In  this  case,  however,  the 
substances  must  reach  the  sensory  membrane  in  a  gaseous  state,  or  in  ex- 


j§T" 


XII 


Fig.  426. — Nerves  of  the  Septum  Nasi,  Seen  from  the  Right  Side.  Xf . — /,  The  olfactory  bulb; 
i,  the  olfactory  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  descending  to 
be  distributed  on  the  septum;  2,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthal- 
mic nerve;    3,  naso-palatine  nerves.      (From  Sappey,  after  Hirschfeld  and  Leveille.) 

tremely  fine  division  so  that  it  can  quickly  enter  into  solution  in  the  moisture 
on  the  sensitive  mucous  surface.  The  odorous  particles  are  carried  to  the 
membrane  by  inspiratory  currents  of  air. 

The  Olfactory  Apparatus.      The  essential  parts  of  the  olfactory  ap- 
paratus  are  the  nasal  sensory  or  olfactory  membrane  to  receive  the  special 
stimuli,  and  the  nervous  apparatus  to  conduct  the  olfactory  nerve-impulse  to 
the  sensory  area  in  the  cortex  cerebri  for  its  perception. 
.    The  nose  is  not  entirely  an  organ  for  the  seat  of  smell.     In  fact  the  nasal 
39 


610  THE     SENSES 

cavities  are  divided  into  three  districts  tailed  respectively:  Regio  vestibularis, 
which  is  the  entrance  to  the  cavity.  It  is  lined  with  a  mucous  membrane  very 
closely  resembling  the  skin,  and  guarded  by  hairs  and  by  sebaceous  glands. 
2,  Regio  respiratoria,  which  includes  the  lower  and  middle  meatus  of  the 
nose.     It  is  covered  with  mucous  membrane  of  stratified  columnar  ciliated 


Fig.  427. — Nerves  of  the  Outer  Walls  of  the  Nasal  Fosss.  1,  Network  of  the  branches  of 
the  olfactory  nerve,  descending  upon  the  region  of  the  superior  and  middle  turbinated  bones; 
2,  external  twig  of  the  ethmoidal  branch  of  the  nasal  nerves;  3,  spheno-palatine  ganglion;  4, 
ramification  of  the  anterior  palatine  nerves;  5,  posterior,  and  6,  middle  divisions  of  the  palatine 
nerves;  7,  branch  to  the  region  of  the  inferior  turbinated  bone;  8,  branch  to  the  region  of  the 
superior  and  middle  turbinated  bones;  9,  naso-palatine  branch  to  the  septum  cut  short.  (From 
Sappey,  after  Hirschfeld  and  Leveille\) 

epithelium.  The  mucosa  is  thick  and  consists  of  fibrous  connective  tissue; 
it  contains  a  certain  number  of  tubular  mucous  and  serous  glands.  3,  Regio 
olfactoria.  This  includes  the  anterior  two-thirds  of  the  superior  meatus,  the 
middle  meatus,  and  the  upper  half  of  the  septum  nasi,  figures  427  and  428. 
It  is  of  a  yellowish  color.  It  consists  of  a  thicker  mucous  membrane  than 
in  2,  made  up  of  loose,  areolar  connective  tissue  covered  by  epithelium  of  a 
special  variety,  resting  upon  a  basement  membrane.  The  cells  of  the  epithe- 
lium are  of  two  principal  kinds:  a,  columnar  epithelial  cells  whose  function 
is  to  support  b,  the  bipolar  olfactory  cells.  The  epithelial  cells  are  prismatic 
in  shape  and  have  upon  their  surfaces  facets  into  which  the  olfactory  cells 
fit  themselves,  figure  428,  e.  They  are  thus  analogous  to  the  cells  of  Muller 
of  the  retina.  The  olfactory  cells  have  an  oblong  or  fusiform  shape,  which 
is  mainly  determined  by  the  large  nucleus.  The  thin  protoplasmic  body  has 
two  processes,  an  external  and  an  internal.  The  external  is  large  and  passes 
up  to  the  free  surface,  to  end  in  a  small  bunch  of  fibrils  that  are  not  vibratile. 
The  internal  process  is  very  fine,  often  varicose,  and  passes  through  the 
cribriform  plate  to  form  a  glomerular  basket  with  the  branches  of  the  mitral 
cells  of  the  olfactory  bulb. 


THE     OLFACTORY     APPARATUS 


611 


The  olfactory  bulb  must  be  studied  in  relation  with  the  nerve  fibers  and 
olfactory  cells  with  which  it  is  connected.  These  parts  together  form  a  sen- 
sor}- end-organ  which  resembles  in  many  respects  the  retina.  The  discovery 
of  its  true  structure  has  thrown  a  flood  of  light  on  the  architecture  of  the  nerve 
centers  as  a  whole. 

The  olfactory  bulb  is  not  a  nerve,  but  a  modification  of  the  brain  cortex. 
A  transection  shows  it  to  be  made  up  of  four  layers:    i,  Peripheral  fibers.    2, 
Olfactory  glomerules.     3,  Layer  of  mitral  cells. 
4,  Layer  of  granular  cells  and  deep  nerve  fibers. 

The  first  and  external  layer  is  composed  of 
the  fine  nerve  fibrils  of  the  olfactory  nerves. 
They  pass  through  the  cribriform  plate  of  the 
ethmoid,  arising  from  the  olfactory  cells  of  which 
they  are  processes. 

The  glomerular  layer  contains  numbers  of 
small  round  bodies  whose  structure  shows  that 
they  are  made  up  of  the  interlocking  expansions 
of  the  olfactory  fibers,  on  the  one  hand,  and  of 
the  branches  of  the  '"mitral"  cells,  on  the  other. 
These  are  mingled  in  a  close  network,  but  do  not 
anastomose.  It  was  by  the  study  of  these  bodies 
in  part  that  the  fact  of  the  non-continuity  of  the 
neurones  was  demonstrated,  figure  429.  This 
layer  also  contains  small  fusiform  cells  with 
branching  dendrites  that  extend  outward  to  the 
glomeruli.  Each  has  an  axis-cylinder  process 
which  passes  inward  to  join  the  fibers  of  the 
internal  olfactory  nerves. 

The  layer  of  mitral  cells  contains  large 
cells,  some  of  them  triangular  and  some  in  the 
shape  of  a  miter.  They  have  numerous  den- 
drites, one  of  which  passes  into  a  glomerulus  and 
then  breaks  up  in  a  fine  arborization.  An  axis- 
cylinder  process  passes  off  from  the  inner  surface 
and  is  continued  as  an  internal  olfactory  nerve  fiber  in  the  olfactory  tract. 

The  layer  of  granules  and  central  fibers  contains  a  large  number  of  very 
small  nerve  cells,  which  are  peculiar  in  that  they  have  no  axis-cylinder. 
Their  dendrites  extend  chiefly  into  the  layer  of  mitral  cells.  They  resemble 
the  spongioblasts  of  the  retina  and  probably  have  commissural  functions. 
This  layer  has  also  some  small  star-shaped  cells  whose  dendrites  end  in  the 
mitral-cell  layer.  Among  these  cells  run  numerous  fibers,  chiefly  from  the 
mitral  cells  and  the  fusiform  cells  of  the  glomerular  layer.  The  general  ar- 
rangement is  shown  in  figure  429. 


Fig.  428. — Bipolar  Olfactory 
Cells  from  the  Nasal  Fossae  of 
the  Rat  (Full-term  Fetus).  A, 
Epithelium  of  the  olfactory 
mucosa;  e,  epithelial  cells;  f,  f, 
nerve  cells;  i,  nerve  fibers  ter- 
minating freely  on  the  epithelial 
surface;  h,  olfactory  nerve  fibers; 
g,  sensory  nerve  derived  from  the 
trigeminus.      (Cajal.) 


612 


THE    SENSES 


The  Stimulation  of  the  Olfactory  Membrane.  The  extent  of  the 
nasal  mucous  surfaces,  and  of  the  frontal  and  antral  sinuses  connected  with 
them,  might  suggest  that  the  sensory  olfactory  surface  is  widely  distributed, 
but  such  is  not  the  case.  Air  impregnated  with  vapor  of  camphor  has  been 
injected  into  the  frontal  sinus  through  a  fistulous  opening,  and  odorous  sub- 
stances have  been  injected  into  the  antrum  of  Highmore;  but  in  neither  case 
was  any  odor  perceived  by  the  patient.  All  parts  of  the  nasal  cavities  are 
endowed  with  cutaneous  sensibility  by  the  nasal  branches  of  the  first  and 


Fig.  429. — Principal  Constituent  Elements  of  the  Olfactory  Bulb  of  a  Mammal.     (Van  Gehuch- 

ten.) 

second  divisions  of  the  fifth  nerve,  hence  the  sensations  of  cold,  heat,  itching, 
tickling,  and  pain,  and  the  sensation  of  tension  or  pressure  in  the  nostrils. 
That  these  nerves  cannot  perform  the  functions  of  the  olfactory  nerves  is 
proved  by  cases  in  which  the  sense  of  smell  is  lost,  while  the  mucous  mem- 
brane of  the  nose  remains  susceptible  to  the  various  modifications  of  the 
sense  of  touch.  But  it  is  often  difficult  to  distinguish  the  sensation  of  smell 
from  that  of  mere  feeling,  and  to  ascertain  what  belongs  to  each  separately. 
This  is  true  particularly  of  the  sensations  excited  by  acrid  vapors  in  the  nose, 
as  of  ammonia,  horse-radish,  mustard,  etc.,  and  the  difficulty  is  the  greater 
when  it  is  remembered  that  these  acrid  vapors  have  nearly  the  same  action 
upon  the  mucous  membrane  of  the  eyelids. 


THE     STIMULATION     OF    THE     OLFACTORY     MEMBRANE  613 

The  true  olfactory  membrane  is  limited  to  the  small  area  on  either  side 
of  the  superior  meatus  and  supplied  by  the  olfactory  nerve.  It  is  stimulated 
by  odorous  substances  when  they  penetrate  the  upper  chamber  of  the  nose. 
Currents  of  air  can  be  drawn  over  this  membrane  more  certainly  and  effect- 
ively by  sniffing  the  air,  as  noticed  in  the  acts  of  a  dog  following  the  trail. 
The  odorous  particles  must  come  into  contact  with  the  olfactory  cells  when 
in  solution  in  the  moisture  over  the  surface  and  produce  its  stimulus  by  chemi- 
cal change.  Mere  presence  in  solution  is  not  always  adequate  to  a  stimula- 
tion. It  seems  that  movement  over  the  surface  is  necessary,  at  least  to  effective 
stimulation.  Haycraft  has  repeated  some  of  the  older  experiments  and  finds 
that  eau  de  Cologne  can  be  introduced  into  the  nasal  cavity  in  warm  saline 
solutions  without  producing  a  sensation  of  smell  even  when  10  per  cent  solu- 
tions are  used.  He  also  showed  that  Cologne,  bergamot,  etc.,  can  be  slowly 
diffused  into  the  nasal  cavity  without  producing  a  stimulus.  If,  while  the 
vapor  is  thus  in  the  nasal  cavity,  the  nostril  be  closed  and  the  person  goes 
into  pure  air  and  breathes,  then  an  odorous  sensation  is  at  once  experienced. 
This  shows  that  even  odorous  gases  "  must  be  moved  over  the  olfactory 
surface"  in  order  to  produce  a  stimulus. 

The  presence  of  bodies  in  quantities  so  minute  as  to  be  undiscernible 
even  by  spectrum  analysis,  0.00000003  °f  a  grain  of  musk,  can  be  distinctly 
smelt  (Valentin).  Opposed  to  the  sensation  of  an  agreeable  odor  is  that  of 
a  disagreeable  or  disgusting  odor,  which  corresponds  to  the  sensations  of  pain, 
dazzling  and  disharmony  of  colors,  and  dissonance  in  the  other  senses.  The 
cause  of  this  difference  in  the  effect  of  different  odors  is  unknown;  but  this 
much  is  certain,  that  odors  are  pleasant  or  offensive  in  a  relative  sense  only, 
for  many  animals  pass  their  existence  in  the  midst  of  odors  which  to  us  are 
highly  disagreeable.  A  great  difference  in  this  respect  is,  indeed,  observed 
among  men.  Many  odors,  generally  thought  agreeable,  are  to  some  per- 
sons intolerable;  and  different  persons  describe  differently  the  sensations 
that  they  severally  derive  from  the  same  odorous  substances.  There  seems 
also  to  be  in  some  persons  an  insensibility  to  certain  odors,  comparable  with 
that  of  the  eye  to  certain  colors;  and  among  different  persons,  as  great  a 
difference  in  the  acuteness  of  the  sense  of  smell  as  among  others  in  the  acute- 
ness  of  sight.  We  have  no  exact  proof  that  a  relation  of  harmony  exists 
between  odors  as  between  colors  and  sounds,  though  it  is  probable  that  such 
is  the  case,  since  it  certainly  is  so  with  regard  to  the  sense  of  taste.  Such  a 
relation  would  account  in  some  measure  for  the  different  degrees  of  perceptive 
power  in  different  persons;  for  as  some  have  no  ear  for  music,  so  others  have 
no  clear  appreciation  of  the  relation  of  odors,  and  therefore  little  pleasure 
in  them. 

Most  of  the  substances  taken  as  foods  into  the  mouth  give  off  odorous 
particles  that  stimulate  the  olfactory  membrane.  In  fact,  the  chief  elements 
in  food  flavors  are  not  tastes,  but  smells,  or  combinations  of  the  two.     This 


614  THE     SENSES 

is  particularly  true  of  meats.  Meats  are  especially  prized  for  their  delicate 
flavors,  and  cooking  is  performed  to  bring  out  these  flavors.  Yet  meat  has 
little  taste  other  than  salt;  the  so-called  tastes  are  due  to  odorous  particles 
entering  the  nostril  and  stimulating  the  olfactory  membrane  at  the  same 
moment  the  taste  buds  of  the  mouth  are  stimulated. 

Subjective  sensations  occur  frequently  in  connection  with  the  sense  of 
smell.  Often  a  person  smells  something  which  is  not  present,  and  which 
other  persons  cannot  smell;  this  is  very  frequent  with  nervous  persons 
but  it  occasionally  happens  to  every  one.  In  a  man  who  was  conscious  of  a 
bad  odor,  the  arachnoid  was  found  after  death  to  be  beset  with  deposits  of 
bone,  and  a  lesion  in  the  middle  of  the  cerebral  hemispheres  was  also  dis- 
covered. Dubois  was  acquainted  with  a  man  who,  ever  after  a  fall  from 
his  horse,  which  occurred  several  years  before  his  death,  believed  that  he 
smelt  a  bad  odor. 

III.    HEARING    AND    EQUILIBRATION. 
THE  ANATOMY  OF  THE  EAR. 

For  descriptive  purposes,  the  Ear,  or  Organ  of  Hearing,  is  divided  into 
three  parts,  i,  the  external,  2,  the  middle,  and  3,  the  internal  ear.  The  first 
two  are  only  accessory  structures  to  the  third,  which  contains  the  essential 
parts  of  the  organ  of  hearing.  The  accompanying  figure,  430,  shows  very 
well  the  relation  of  these  divisions  to  each  other. 

The  External  Ear.  The  external  ear  consists  of  the  pinna  or 
auricle  and  the  external  auditory  canal  or  meatus. 

The  principal  parts  of  the  pinna,  figure  430,  are  two  prominent  rims  en- 
closed one  within  the  other,  the  helix  and  antihelix,  and  inclosing  a  central 
hollow  named  the  concha  ;  in  front  of  the  concha,  a  prominence  directed 
backward,  the  tragus,  and  opposite  to  this  one  directed  forward,  the  anti- 
tragus.  From  the  concha,  the  auditory  canal  passes  inward  and  a  little 
forward  to  the  membrana  tympani,  to  which  it  thus  serves  to  convey  the 
vibrations  of  the  air.  It  consists  of  a  fibro-cartilage  tube  lined  by  skin  con- 
tinuous with  that  of  the  pinna,  and  extending  over  the  outer  part  of  the  mem- 
brana tympani.  Fine  hairs  and  sebaceous  glands  are  present  toward  the 
outer  part  of  the  canal,  while  deeper  in  the  canal  are  small  glands,  resembling 
the  sweat  glands  in  structure,  which  secrete  the  cerumen. 

Regarding  the  external  ear,  therefore,  as  a  collector  and  conductor  of 
sonorous  vibrations,  all  its  inequalities,  elevations,  and  depressions  become 
of  evident  importance;  for  those  elevations  and  depressions  upon  which  the 
undulations  fall  will  tend  to  intensify  certain  sound  waves  while  not  affecting 
others.  It  is  thought  that  this  forms  at  least  an  aid  in  determining  the  direc- 
tion whence  a  sound  comes. 


THE     .MlliniJ-:     EAR     OK     TV.Ml'AM   M 


615 


The  Middle  Ear  or  Tympanum.  The  middle  ear,  or  tympanum, 
3,  figure  430,  is  separated  by  the  membrana  tympani  from  the  external  auditory 
canal.  It  is  a  cavity  in  the  temporal  bone,  opening  through  its  anterior  and 
inner  wall  into  the  Eustachian  tube. 

The  Eustachian  canal  establishes  communication  between  the  tympanic 
cavity  and   pharynx,  thus  equalizing  the  air  pressure  on  the   sides  of   the 


Fig.  430. — Diagrammatic  View  from  Before  of  the  Parts  Composing  the  Organ  of  Hearing  of 
the  Left  Side.  The  temporal  bone  of  the  left  side,  with  the  accompanying  soft  parts,  has  been 
detached  from  the  head,  and  a  section  has  been  carried  through  it  transversely,  so  as  to  remove 
the  front  of  the  meatus  externus,  half  the  tympanic  membrane,  the  upper  and  anterior  wall  of 
the  tympanum  and  Eustachian  tube.  The  meatus  internus  has  also  been  opened,  and  the  bony 
labyrinth  exposed  by  the  removal  of  the  surrounding  parts  of  the  petrous  bone.  1 ,  The  pinna 
and  lobe;  2,  2',  meatus  externus;  2',  membrana  tympani;  3,  cavity  of  the  tympanum;  3',  its 
opening  backward  into  the  mastoid  cells;  between  3  and  3',  the  chain  of  small  bones;  4,  Eusta- 
chian tube;  s.  meatus  internus,  containing  the  facial  (uppermost)  and  the  auditory  nerves;  6, 
placed  on  the  vestibule  of  the  labyrinth  above  the  fenestra  ovalis;  a,  apex  of  the  petrous  bone; 
b,  internal  carotid  artery;  c,  styloid  process;  d,  facial  nerve  issuing  from  the  stylo-mastoid  foramen; 
e,  mastoid  process;    f,  squamous  part  of  the  bone  covered  by  integument,  etc.      (Arnold.) 


S   B 


15     D 


E 


Pig.  431. — Tympanic  Ossicles  of  Left  Ear.  A,  Incus  seen  from  the  front;  B,  malleus,  viewed 
from  behind;  C,  incus,  and  D.  malleus,  seen  from  inner  aspect;  E,  stapes,  1,  Body  of  incus,  with 
articular  surface  for  head  of  malleus;  2,  processus  longus;  3,  processus  lenticularis;  4,  articular 
surface  for  incus;  5,  head,  (>,  neck;  7,  processus  bre vis;  8,  manubrium,  >..  body;  to,  short  proc- 
ess; ii,  long  process;  12,  processus  longus;  13,  head;  14,  facet  for  incus;  15,  manubrium,  16, 
head;   17,  neck;   18,  crus  pnterius;    19,  crus  posterius;    20,  foot  plate. 


61C 


Till':    SENSES 


tympanic  membrane,  serving  the  same  mechanical  purpose  as  the  vent-hole 
in  a  snare  or  bass  drum.  The  cavity  of  the  tympanum  communicates  pos- 
teriorly with  air  cavities,  the  mastoid  cells,  in  the  mastoid  process  of  the  tem- 
poral bone;  but  its  only  opening  to  the  external  air  is  through  the  Eustachian 
tube.     The  cavity  of  the  tympanum  is  lined  with  mucous  membrane,  the 


Recessus  epitympanieus 
Body  of  incus 

Short  process  of  incus 
Ligament  of  incus 


Chorda  tympani  nerve 
Pyramid,  with  tendon 

of  stapedius  muscle ^ 

issuing  from  it 


Superfo'r'liganjent  of  malleus 
Head  of  malleus 


Foot  of  stapes 


Anterior  ligament  of  malleus 


Handle  of  malleus 


Tensor  tympani  muscle 


Processus 

cochlea  riformis 
Osseous  part  of 
Eustachian  tube 


Fig.  432. — Left  Membrana  Tympani  and  Chain  of  Tympanic  Ossicles  (Seen  from  Inner 
Aspect).     (Cunningham.) 


epithelium  of  which  is  ciliated  and  continuous  with  that  of  the  pharynx.  It 
contains  a  chain  of  small  bones,  ossicula  anditus,  which  extends  from  the 
membrana  tympani  to  the  fenestra  ovalis. 

The  Membrana  Tympani.  The  tympanic  membrane  is  placed  in  a  slant- 
ing direction  at  the  bottom  of  the  external  canal,  its  plane  being  at  an  angle 
of  about  forty-five  degrees  with  the  lower  wall  of  the  canal.  It  is  formed 
chiefly  of  a  tough  and  tense  fibrous  membrane,  the  edges  of  which  are  set 
in  a  bony  groove.  Its  outer  surface  is  covered  by  a  continuation  of  the  epithe- 
lial lining  of  the  auditory  canal,  its  inner  surface  with  part  of  the  mucous 
membrane  of  the  middle  ear. 

The  Tympanic  Ossicles.  The  ear  bones,  or  ossicles,  are  named  the 
malleus,  incus,  and  stapes.  The  malleus  is  attached  by  a  long  slightly  curved 
process,  called  its  handle,  to  the  membrana  tympani,  the  line  of  attachment 
being  vertical,  including  the  whole  length  of  the  handle,  and  extending  from 
the  upper  border  to  the  center  of  the  membrane.  The  head  of  the  malleus 
is  irregularly  rounded;  its  neck,  or  the  line  of  boundary  between  it  and  the 
handle,  supports  a  short  conical  process  which  receives  the  insertion  of  the 
tensor  tympani  muscle.  The  incus,  shaped  like  a  bicuspid  molar  tooth,  is 
articulated  by  its  broader  part  to  the  malleus.  Of  its  two  fang-like  processes, 
one  directed  backward  has  a  free  end  lodged  in  a  depression  in  the  mastoid 
bone;    the  other,  curved  downward  and  more  pointed,  articulates  by  means 


THE     INTERNAL     EAB 


(II 


of  a  roundish  tubercle  with  the  stapes.  The  stapes  is  a  little  bone  shaped 
exactly  like  a  stirrup,  of  which  the  base  or  bar  fits  into  the  fenestra  ovalis. 
The  stapedius  muscle  is  attached  to  the  neck  of  the  stapes. 

The  bones  of  the  ear  are  covered  with  mucous  membrane  reflected  over 
them  from  the  wall  of  the  tympanum.  They  are  movable  both  altogether 
and  one  upon  the  other.  The  malleus  moves  and  vibrates  with  every  move- 
ment and  vibration  of  the  membrana  tympani,  and  its  movements  are  com- 
municated through  the  incus  to  the  stapes,  and  through  the  stapes  to  the 
membrane  closing  the  fenestra  ovalis.  The  malleus,  also,  is  movable  in  its 
articulation  with  the  incus.  The  membrana  tympani  which  moves  the  long 
process  of  the  malleus  is  altered  in  its  degree  of  tension  by  the  degree  of  con- 
traction of  the  tensor  tympani  muscles.  The  stapes  is  movable  on  the  process 
of  the  incus,  the  contractions  of  the  stapedius  muscle  draws  it  outward.  The 
axis  round  which  the  malleus  and  incus  rotate  is  the  line  joining  the  pro- 
cessus gracilis  of  the  malleus  and  the  posterior  process  of  the  incus. 

The  Internal  Ear.  The  internal  ear,  or  labyrinth,  constitutes  the 
proper  organ  of  hearing.  It  contains  special  epithelial  structures  to  which 
are  distributed  the  auditory  nerve.  The  organ  is  located  in  a  cavity  in  the 
petrous  bone,   called  the  osseus  labyrinth.     The  auditory  organ  within  is 


Fig.  433- 


Fig.  434. 


Fig.  433.' — Right  Bony  Labyrinth.  Viewed  from  the  Outer  Side.  The  specimen  here  represented 
is  prepared  by  separating  piecemeal  the  looser  substance  of  the  petrous  bone  from  the  dense  walls 
which  immediately  enclose  the  labyrinth.  1,  The  vestibule;  2,  fenestra  ovalis;  3,  superior  semi- 
circular canal;  4,  horizontal  or  external  canal;  5,  posterior  canal;  *,  ampullae  of  the  semicircular 
canals;  6,  first  turn  of  the  cochlea;  7,  second  turn;  8,  apex;  9,  fenestra  rotunda.  The  smaller 
figure  in  outline  below  shows  the  natural  size.      X  2.5.     (Sommering.) 

Fm.  434. — View  of  the  Interior  of  the  Left  Labyrinth.  The  bony  wall  of  the  labyrinth  is  re- 
moved superiorly  and  externally.  1,  Fovea  hemielliptica;  2.  fovea  hemispherica;  3,  common 
opening  of  the  superior  and  posterior  semicircular  canals;  4,  opening  of  the  aqueduct  of  the 
vestibule;  5.  the  superior,  6,  the  posterior,  and  7,  the  external  semicircula-  canals;  8,  spiral  tube 
of  the  cochlea  (scala  tympani);  9.  opening  of  the  aqueduct  of  the  cochlea;  10,  placed  on  the  lamina 
spiralis  in  the  scala  vestibuli.      X2.5.      (Sommering.) 


called  the  membranous  labyrinth.  The  membranous  labyrinth  contains  a 
fluid  called endolymph  ;  while  outside  it,  between  it  and  the  osseous  labyrinth, 
is  a  fluid  called  perilymph.     This  is  not  a  pure  lymph,  as  it  contains  mucin. 


(J  IS 


THE    SENSES 


The  osseous  labyrinth  consists  of  three  principal  parts,  namely  the  vesti- 
bule, the  cochlea,  and  the  semicircular  canals,  containing  the  respective  divisions 
of  the  membranous  labyrinth.  The  osseous  labyrinth  possesses  openings  on 
its  inner  wall  for  the  entrance  of  the  divisions  of  the  auditory  nerve  from  the 
cranial  cavity,  in  its  outer  wall  the  fenestra  ovalis,  2,  figure  433,  an  opening 
filled  by  the  base  of  the  stapes,  and  the  fenestra  rotunda.  The  vestibule 
also  presents  an  opening,  the  orifice  of  the  aqueductus  vestibuli. 

The    Membranous    Labyrinth.      The    membranous    labyrinth    cor- 


Fig.   435- 


-Membranous    Labyrinth  of  a  30  mm.  Human  Fetus.    A,  Viewed  from  its  Lateral 
Aspect;  B,  viewed  from  the  mesial  aspect.      (Streeter.) 


responds  generally  with  the  form  of  the  osseous  labyrinth,  so  far  as  regards 
the  vestibule  and  semicircular  canals,  but  is  separated  from  the  walls  of  these 
parts  by  perilymph,  except  where  the  nerves  enter  into  connection  within  it. 
The  labyrinth  is  a  closed  membrane  containing  endolymph. 

The  Utriculus  and  the  Sacculus.  The  vestibular  portion  of  the  inner  ear 
consists  of  membranous  sacs,  the  upper,  the  utriculus,  the  lower  called  the 
sacculus.  The  former  is  connected  with  the  semicircular  canals,  the  latter 
with  the  cochlea  by  the  cochlear  canal.  The  utriculus  and  the  sacculus  have 
on  their  floors  a  special  patch  of  sensory  epithelium  called  the  macula:.  The 
fibers  of  the  vestibular  divisions  of  the  auditory  nerve  end  in  the  maculae, 


THE     COCHLEA     AND     THE     OIKJAN     OF    CORTI 


<>l!) 


figure  435.     In  the  cavities  of  the  sacculus  and  utriculus  are  small  masses  of 
calcareous  particles  called  otoliths. 

The  Semicircular  Canals.  There  are  three  semicircular  canals  for  each 
ear,  one  horizontal  and  two  vertical  ones  placed  almost  at  right  angles  to 
each  other.  The  three  canals,  therefore,  occupy  the  three  planes  of  space. 
Each  has  a  considerable  enlargement  or  swelling,  called  an  ampulla.  The 
epithelium  of  the  ampulla  is  modified  at  the  point  of  entrance  of  the  nerve 
into  a  thickened  hillock  called  the  crista  acustica.  This  epithelium  is  com- 
posed of  rod  cells  or  supporting  cells  which  extend  the  full  thickness  of  the 
crista,  and  of  hair  cells,  which  occupy  the  inner  or  free  half  of  the  crista. 
The  hair  cells  are  the  sensory  cells.  They  have  hair-like  processes  which 
project  from  the  free  ends  of  the  cells  out 
into  the  endolymph  of  the  cavity.  Nerve 
fibrils  run  up  into  the  crista  and  apparently 
form  terminal  arborizations  about  the  hair 
ceils,  or,  according  to  some  observers,  end 
in  the  cells. 

The  Cochlea  and  the  Organ  of  Corti. 
The  membranous  cochlea  is  located  in 
the  spiral  canal  in  the  petrous  bone,  called 
the  cochlear  canal.  It  is  attached  to  the 
wall  of  the  cavity  between  the  fenestra 
ovalis  and  the  fenestra  rotunda,  and  to  the 
outer  wall  of  the  canal  and  the  free  border  of  the  lamina  spiralis  almost,  but 
not  quite,  to  its  summit.  A  small  cavity  is  thus  left  around  the  upper  end 
of  the  cochlea  connecting  the  scala  vestibuli  above  with  the  scala  tympani 
below.  A  cross-section  through  the  cochlear  canal  shows  the  relations  of 
the  cochlear  canal  which  was  named  scala  media  by  the  earlier  anatomists. 
The  free  portion  of  the  membranous  wall  above  is  called  the  membrane  oj 
Reisner,  while  that  below  is  called  the  basilar  membrane.  The  basilar  mem- 
brane supports  the  special  sensory  apparatus  for  the  reception  of  stimuli 
of  sound  waves. 

Organ  of  Corti.  The  basilar  membrane  supports  cells  of  several  types. 
About  midway  between  the  outer  edge  of  the  lamina  spiralis  and  the  outer 
wall  of  the  cochlea  are  situated  the  rods  oj  Corti.  Viewed  sideways,  they  are 
seen  to  consist  of  an  external  and  internal  pillar,  each  rising  from  an  expanded 
foot  or  base  on  the  basilar  membrane,  figure  438.  They  slant  inward 
toward  each  other,  and  each  ends  in  a  swelling  termed  the  head,  the  head  of 
the  inner  pillar  overlying  that  of  the  outer,  figure  438.  Each  pair  of  pillars 
forms,  as  it  were,  a  pointed  roof  arching  over  a  space,  and  by  a  succession 
of  them  a  little  tunnel  is  formed.  It  has  been  estimated  that  there  are  about 
three  thousand  of  these  pairs  of  rods  of  Corti  between  the  base  of  the  cochlea 
and  its  apex.     They  are  found  progressively  to  increase  in  length,  and  be- 


Fig.  436. — View  of  the  Osseous 
Cochlea  Divided  through  the  Middle. 
1,  Centra!  canal  of  the  modiolus;  2, 
lamina  spiralis  ossea;  3,  scala  tym- 
pani; 4,  scala  vestibuli;  5,  porous 
substance  of  the  modiolus  near  one  of 
the  sections  of  the  canalis  spiralis 
modioli.      X5.      (Arnold.) 


620 


THE     SENSES 


come  more  oblique;  in  other  words,  the  tunnel  becomes  wider,  but  diminishes 
in  height  as  we  approach  the  apex  of  the  cochlea. 

Leaning  against  the  rods  of  Corti  and  apparently  supported  by  them 
are  sensory  cells  or  hair  cells.  The  hair  cells  are  in  two  series,  the  inner  and 
the  outer  hair  cells.  The  former  consist  of  a  single  layer,  the  latter  of  three 
or  four  layers,  figure  438.  There  are  two  additional  types  of  supporting  cells, 
the  cells  of  Deiters  and  of  Hensen.  The  whole  structure  when  viewed  from 
above  bears  a  remarkable  resemblance  to  the  keyboard  of  a  piano. 

The  cochlear  division  of  the  auditory  nerve  enters  the  base  of  the  modiolus 
and  sends  a  spiral  whorl  of  fibers  out  under  the  spiral  lamina      The  gan- 


is 

mm 
Si 


Scala 
vestihuli 


cochleaTis 


Scala  tympani 


Fig.  437- — Semidiagrammatic  Section  of  a  Cochlear  Whorl.      (After  Heitzmann.) 

glionic  cells  of  the  cochlear  division  of  the  auditory  nerve  are  located  in  the 
base  of  the  lamina  where  they  form  the  spiral  ganglion.  The  nerve  fibers 
from  the  ganglion  cells  pass  out  through  small  holes  in  the  periphery  of  the 
spiral  plate  of  bone,  to  enter  the  organ  of  Corti.  Here  they  form  small  longi- 
tudinal bundles  that  quickly  end  about  the  hair  cells. 


THE  PHYSIOLOGY  OF  HEARING. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are  means  for  con- 
ducting sound.  Since  all  matter  is  capable  of  propagating  sonorous  vibra- 
tions, the  simplest  conditions  must  be  sufficient  for  mere  hearing;  since  all 
substances  surrounding  the  auditory  apparatus  would  stimulate  it.  The  com- 
plex development  of  the  organ  of  hearing,  therefore,  must  have  for  its  object 


THE     PHYSIOLOGY     <>!'     HEARING 


621 


the  more  effective  propagation  of  the  sonorous  vibrations  and  their  intensi- 
fication by  resonance;  and,  in  fact,  the  whole  of  the  acoustic  apparatus  may 
be  shown  to  have  reference  to  these  principles. 

The  external  ear  and  the  auditory  passages  influence  the  propagation  of 
sound  to  the  tympanum  by  collecting  from  the  atmosphere  the  sonorous  undu- 
lations that  strike  against  the  external  ear  and  by  transmitting  them  by  the 
air  in  the  passage  to  the  membrana  tympani. 

In  animals  living  in  the  atmosphere,  the  sonorous  vibrations  are  con- 
veyed to  the  auditory  epithelium  through  three  different  media  in  series; 


linbtts 


mcmbrana  tectoria 


outer  hair-cells 
U 


nerve  fibres 


inner  rod    vas    basilar 

tpiralc    membrane 


outer    cells  of  Deiten 
rod 


Fig.  438. — Semidiagrammatic  Representation  of  the  Organ  of  Corti  and  Adjacent  Structures. 
(Merkel-Henle.)  a.  Cells  of  Hensen;  b,  cells  of  Claudius;  c,  internal  spiral  sulcus;  x,  Nuel's  space. 
The  nerve  fibers  (dendrites  of  cells  of  the  spinal  ganglion)  are  seen  passing  to  Corti's  organ  through 
openings  (foramina  nervosa)  in  the  bony  spiral  lamina.  The  black  dots  represent  longitudinally- 
running  branches,  one  bundle  lying  to  the  inner  side  of  the  inner  pillar,  a  second  just  to  the  outer 
side  of  the  inner  pillar  within  Corti's  tunnel,  the  third  beneath  the  outer  hair  cells. 


namely,  the  air  of  the  external  ear  and  meatus,  which  sets  in  vibration  the 
tympanic  membrane,  the  solid  chain  of  auditory  ossicles,  and  the  fluid  of  the 
labyrinth.  Sonorous  vibrations  are  imparted  too  imperfectly  from  air  to 
the  solid  structures  of  the  body  as  a  whole  for  the  propagation  of  sound  to 
the  internal  ear  to  be  adequately  effected  by  that  means  alone.  In  passing 
from  air  directly  into  water,  sonorous  vibrations  suffer  also  a  considerable 
diminution  of  their  strength;  but  if  a  tense  membrane  exists  between  the 
air  and  the  water,  the  sonorous  vibrations  are  communicated  from  the  former 
to  the  latter  medium  with  very  great  intensity.  This  fact,  of  which  Miiller 
gives  experimental  proof,  furnishes  at  once  an  explanation  of  the  use  of  the 
fenestra  ovalis  and  of  the  membrane  closing  it.  It  is  the  means  of  com- 
municating, in  full  intensity,  the  vibrations  of  the  ear  bones,  or,  in  their  absence, 
of  the  air  in  the  tympanum,  to  the  fluid  of  the  labyrinth.  The  vibration  of 
the  fluid,  the  perilymph  and  endolymph,  of  the  internal  ear,  sets  the  basilar 
membrane  in  vibration  and  in  consequence  stimulates  the  sensory  apparatus 


622  THE    SENSES 

resting  upon  It.  This  lasl  is  the  essential  stimulating  act,  while  all  that  pre- 
cedes is  more  or  less  accessory  or  contributory  to  this  act.  Just  what  the 
accessory  apparatus  contributes  can  best  be  understood  by  an  examination 
of  the  stimulus  and  the  sensation  which  results  from  its  action. 

Sound.  Any  elastic  body,  e.g.,  air,  a  membrane,  or  a  string,  per- 
forming a  certain  number  of  regular  vibrations  per  second,  gives  rise  to 
what  is  termed  a  musical  sound  or  tone.  We  must,  however,  distinguish 
between  a  musical  sound  and  a  mere  noise;  the  latter  being  due  to  irregular 
vibrations. 

Musical  sounds  are  distinguished  from  each  other  by  three  qualities: 
i,  Strength  or  Intensity,  which  is  due  to  the  amplitude  or  length  of  the  wave 
of  vibrations.  2,  Rate,  the  number  of  vibrations  in  a  second.  3,  Quality, 
or  Timbre,  the  peculiar  property  by  which  we  distinguish  the  same  note 
sounded  on  two  instruments,  e.g.,  a  piano  and  a  flute.  It  has  been  proved 
by  Helmholtz  to  depend  on  the  number  of  secondary  tones,  termed  harmonics, 
which  are  present  with  the  predominating  or  fundamental  tone.  That  is, 
rhythmic  vibrations  are  either  simple  in  form,  like  the  vibrations  of  a  reed 
or  tuning  fork,  or  compound,  like  the  vibrations  of  a  violin  or  piano  string. 
If  the  string  of  a  violin  is  plucked  it  not  only  vibrates  as  a  whole,  but  in  seg- 
ments in  the  ratio  of  one,  two,  three,  etc.  The  form  of  air  wave  that  is  pro- 
duced by  several  such  vibrating  bodies  is  very  complex  indeed,  as,  for  example, 
when  an  orchestra  is  playing. 

The  compound  wave  can  be  analyzed  into  its  constituent  elements  by  a 
system  of  resonators,  on  the  principle  of  sympathetic  vibration.  If  one 
sounds  a  series  of  musical  notes  before  such  a  system  of  resonators  it  will  be 
found  that  the  tones  and  overtones  are  selected  by  the  resonators  and  made 
more  prominent  so  that  they  can  be  identified. 

The  sensation  of  sound  has  in  it  certain  elements  that  correspond  closely 
with  the  physical  properties  of  sound,  i.e.,  loudness,  pitch,  and  quality.  Loud- 
ness is  dependent  merely  on  the  intensity  of  the  stimulation.  A  sound  wave 
of  great  energy,  for  example,  produces  a  larger  movement  of  the  tympanic 
membrane,  and  it,  through  the  chain  of  bones  and  the  fluid  of  the  internal 
ear,  a  larger  swing  of  the  basilar  membrane,  hence  a  more  intense  stimulus 
of  the  organ  of  Corti. 

Function  of  the  External  and  Middle  Ears.  It  has  already  been 
stated  that  the  external  ear  collects  the  sound  waves  and  conducts  them 
against  the  membrana  tympani.  This  membrane  vibrates  as  a  whole  to 
the  compound  waves  that  impinge  upon  it,  and  thus  serves  for  the  trans- 
mission of  sound  from  the  air  to  the  chain  of  ossicles  of  the  middle  ear.  It  is 
often  compared  to  the  membrane  of  a  drum,  but  there  are  fundamental 
differences. 

When  a  drum  is  struck,  a  certain  definite  fundamental  tone  is  elicited; 
similarly  a  drum  is  thrown  into  vibration  when  certain  tones  are  sounded  in 


FUNCTION    OF     Till:     EXTERNAL     AM)     MIDDLE     EARS 


623 


its  neighborhood,  while  it  is  quite  unaffected  by  others.  In  other  words,  it 
can  take  up  and  vibrate  in  response  only  to  those  tones  whose  vibrations 
nearly  correspond  in  number  with  those  of  its  own  fundamental  tone.  The 
tympanic  membrane  can  take  up  an  immense  range  of  tones  produced  by 
vibrations  ranging  from  30  to  4,000  or  5,000  per  second.  This  would  be  clearly 
impossible  if  it  were  an  evenly  stretched  membrane.  The  fact  is  that  the 
membrana  tympani  is  by  no  means  evenly  stretched,  and  this  is  due  partly 
to  its  slightly  funnel-like  form,  and  partly  to  its  being  connected  with  the 
chain  of  auditory  ossicles.  Further,  if  the  membrane  were  quite  free  in  its 
center,  it  would  go  on  vibrating  as  a  drum  does  some  time  after  it  is  struck; 
each  sound  would   be  prolonged,  leading  to  considerable  confusion.     This 


B 


Fig.   439. — Showing  j4  and  B,  Simple  Pendular  Vibrations,  Separated  by  One  Octave.    C, 
The  form  of  the  curve  produced  by  the  combination  of  .4  and  B. 


evil  is  obviated  by  the  ear  bones,  which  check  the  continuance  of  the  vibra- 
tions like  the  "dampers"  in  a  piano. 

The  vibrations  of  the  membrana  tympani  are  transmitted  by  the  chain 
of  ossicles  to  the  fenestra  ovalis  and  fluid  of  the  labyrinth,  their  dispersion 
in  the  tympanum  being  prevented  by  the  difficulty  of  the  transition  of  vibra- 
tions from  solid  to  gaseous  bodies.  The  necessity  of  the  presence  of  air  on 
the  inner  side  of  the  membrana  tympani,  in  order  to  enable  it  and  the  auditory 
ossicles  to  fulfil  the  objects  just  described,  is  obvious.  Without  this  pro- 
vision, neither  would  the  vibrations  of  the  membrane  be  free  nor  the  chain 
of  bones  isolated,  so  as  to  propagate  the  sonorous  undulations  with  con- 
centration of  their  intensity.  But  while  the  oscillations  of  the  membrana 
tympani  are  readily  communicated  to  the  air  in  the  cavity  of  the  tympanum, 
those  of  the  solid  ossicles  will  not  be  conducted  away  by  the  air,  but  will 
be  propagated  to  the  labyrinth  without  being  dispersed  in  the  tympanum. 

The  propagation  of  sound  through  the  auditory  ossicles  to  the  labyrinth 
must  be  effected  by  oscillations  of  the  bones  as  a  whole. 

The  existence  of  the  membrane  over  the  fenestra  rotunda  permits  approxi- 


62  1. 


TIIK    SENSES 


mation  and  removal  of  the  stapes  to  and  from  the  labyrinth.  When  the 
membrane  of  the  fenestra  ovalis  is  pressed  toward  the  labyrinth  by  the  stapes, 
the  membrane  of  the  fenestra  rotunda  may,  by  the  pressure  communicated 
through  the  fluid  of  the  labyrinth,  be  pressed  toward  the  cavity  of  the  tym- 
panum. The  long  process  of  the  malleus  receives  the  undulations  of  the 
membrana  tympani,  figure  440,  a,  a,  and  of  the  air  in  a  direction  indicated 
by  the  arrows,  nearly  perpendicular  to  itself.  From  the  long  process  of  the 
malleus  they  are  propagated  to  its  head,  b;  thence  into  the  incus,  c,  the 
long  process  of  which  is  parallel  writh  the  long  process  of  the  malleus.     From 

the  long  process  of  the  incus  the  undulations  are 
communicated  to  the  stapes,  d,  which  is  united 
to  the  incus  at  right  angles.  The  several  changes 
in  the  direction  of  the  chain  of  bones  have,  how- 
ever, no  influence  in  changing  the  character  of 
the  undulations,  which  remain  the  same  as  in 
the  meatus  externus.  From  the  long  process 
of  the  malleus  the  undulations  are  communi- 
cated by  the  stapes  to  the  fenestra  ovalis  in  a 
perpendicular  direction.  Increasing  tension  of 
the  membrana  tympani  diminishes  the  facility  of 
transmission  of  sonorous  undulations  from  the 
air  to  it.  It  has  been  inferred,  therefore,  that 
hearing  is  rendered  less  acute  by  increasing  the 
tension  of  the  membrana  tympani.  This  is  ac- 
complished by  the  contractions  of  the  tensor 
tympani  muscle.  The  exact  influence  of  the 
stapedius  muscle  in  the  act  of  hearing  is  un- 
known. It  acts  upon  the  stapes  in  such  a 
manner  as  to  make  it  rest  obliquely  in  the  fenestra  ovalis,  depressing  that 
side  of  the  stapes  on  which  it  is  attached  and  elevating  the  other  side  to 
the  same  extent.     It  seems  to  prevent  too  great  a  movement  of  the  bone. 

The  pharyngeal  orifice  of  the  Eustachian  tube  is  usually  shut.  During 
swallowing,  however,  it  is  opened;  which  may  be  shown  as  follows:  If  the 
nose  and  mouth  be  closed  and  the  cheeks  blown  out,  a  sense  of  pressure  is 
produced  in  both  ears  the  moment  we  swallow.  This  is  due,  doubtless,  to 
the  bulging  out  of  the  tympanic  membrane  by  the  compressed  air,  which  at 
that  moment  enters  the  Eustachian  tube.  The  principal  office  of  the  Eusta- 
chian tube  has  relation  to  the  prevention  of  the  effects  of  increased  tension  of 
the  membrana  tympani.  Its  existence  and  openness  will  provide  for  the 
maintenance  of  the  equilibrium  between  the  air  within  the  tympanum  and 
the  external  air,  so  as  to  prevent  the  inordinate  tension  of  the  membrana 
tympani  which  would  be  produced  by  too  great  or  too  little  pressure  on  either 
side.     While  discharging  this  office  it  serves  as  an  outlet  for  mucus.     If  the 


Fig.  440. — Diagram  to  Illus- 
trate the  Action  of  the  Ossicles 
of  the  Middle  Ear  in  the  Conduc- 
tion of  Sound  to  the  Internal 
Ear. 


THE    FUNCTION    OF    THE    INTERNAL    EAR  625 

tube  were  permanently  open,  the  sound  of  one's  own  voice  would  probably 
be  greatly  intensified,  a  condition  which  would  of  course  interfere  with  the 
perception  of  other  sounds.  At  any  rate,  it  is  certain  that  sonorous  vibra- 
tions can  be  propagated  up  the  tube  to  the  tympanum  by  means  of  a  catheter 
inserted  into  the  pharyngeal  orifice  of  the  Eustachian  tube. 

The  Function  of  the  Internal  Ear.  The  fluids  of  the  labyrinth  re- 
ceive the  sonorous  vibrations  at  the  fenestra  ovalis  and,  we  must  assume, 
conduct  the  same  throughout  the  cavity.  In  all  forms  of  organs  of  hearing 
even  to  the  simplest,  liquid  is  the  medium  through  which  the  auditory  sen- 
sory epithelium  is  stimulated.  We  have  already  seen  that  in  the  mammalian 
ear  there  is  a  special  mechanical  arrangement  to  intensify  the  vibrations  of 
the  fluid  in  the  cochlear  canal. 

The  utriculus,  sacculus,  and  semicircular  canals  are  probably  not  concerned 
with  auditory  function,  but  with  the  sense  of  equilibrium;  hence  they  will 
be  discussed  separately  a  little  later. 

The  cochlea  is  the  special  organ  of  hearing.  When  it  is  set  in  vibrations 
the  movement  stimulates  the  sensory  hair  cells  on  the  basement  membrane, 
producing  a  sensory  impulse  which  is  transmitted  along  the  paths  to  the  brain 
and  there  produces  an  auditory  sensation.  If  the  stimulus  results  from  a 
disturbance  of  an  explosive  or  non-harmonic  nature,  the  sensation  is  inter- 
preted as  a  noise.  If  the  disturbance  is  rhythmic  or  harmonic  and  repeated 
in  sequence  within  certain  limits  of  rate,  then  a  tone  is  perceived. 

The  intensity  of  sound,  the  energy  of  the  disturbance,  affects  the  basilar 
membrane  by  producing  motion  of  varying  amplitude.  This  stimulates  the 
hair  cells  with  greater  or  less  intensity,  which  can  be  detected  by  the  sensorium 
as  loudness.  Loudness  of  the  sound  sensation  is  interpreted  as  intensity  of 
sound  wave. 

The  interpretation  of  pitch  is  accomplished  by  the  ear  through  a  wide 
range  of  rates  of  vibration  that  produce  sensations  of  tone.  The  average 
person  can  perceive  musical  tones  over  a  range  of  vibration  of  from  sixty-four 
double  vibrations  per  second  for  the  lower  notes,  to  four  thousand  and  ninety- 
six  for  the  higher  notes.  These  limits  may  be  extended  to  thirty  per  second 
and  forty  thousand  per  second,  respectively,  but  only  a  small  number  of 
tones  can  be  perceived  outside  of  the  narrower  limits  given  above.  This 
extraordinary  range  of  tone  is  conceivable  only  on  the  supposition  of  local- 
ization of  the  stimulus  in  some  part  of  the  organ.  Most  physiologists  look 
to  the  basilar  membrane  and  the  organ  of  Corti  for  the  localization. 

Suppose  a  simple  tuning  fork  to  be  vibrating  with  a  frequency  of  sixty- 
four  per  second,  then  these  waves  will  be  conducted  through  the  auditory 
apparatus  until  they  fall  on  the  basilar  membrane,  and  will  set  it  in  vibration 
at  the  same  rate.  The  exact  type  of  the  vibration  is  at  present  a  matter  of 
inference.  The  piano  theory  of  Helmholtz  is  probably  the  most  satisfactory. 
It  assumes  that  the  basilar  membrane  vibrates  as  would  a  number  of  strings 
40 


626  THE     SENSES 

set  in  the  transverse  dimension.  In  support  of  this  assumption  it  is  asserted 
that  the  membrane  is  taut  in  the  transverse  and  loose  in  the  longitudinal 
plane.  Retzius  has  estimated  that  it  contains  about  24,000  fibers,  and  that 
it  measures  in  width  at  the  base  0.135  mm-  an<^  a*  tne  apex  0.234  mm.  In 
the  above  illustration  the  vibration  frequency  of  sixty-four  would  supposedly 
set  in  sympathetic  vibration  that  part  of  the  apex  of  the  basilar  membrane 
which  vibrated  in  the  same  frequency,  and  the  sensory  cells  of  the  organ  of 
Corti,  located  over  the  vibrating  fiber,  would  be  stimulated  accordingly.  In 
the  same  way  notes  of  medium  and  of  high  frequency  stimulate  localized 
areas  of  sensory  cells  in  the  middle  and  basal  parts  of  the  organ  of  Corti  and 
produce  sensations  of  corresponding  pitch. 

This  idea  of  localization  of  auditory  sensory  stimulation  makes  it  easier 
to  understand  the  analysis  by  the  ear  of  compound  sonorous  waves.  Such 
waves  impinge  on  the  membrana  tympani  and  are  transmitted  through  the 
conducting  media  unanalyzed,  and  may  be  supposed  to  fall  on  the  basilar 
membrane  as  compound  waves.  The  basilar  fibers  acting  like  so  many 
resonators,  take  up  the  constituent  sonorous  elements  in  sympathetic  vibra- 
tion. In  short,  the  basilar  membrane  is  an  analyzer  in  which  the  compound 
wave  is  reduced  to  its  simple  components,  each  of  which  stimulates  its  cor- 
responding portion  of  the  organ  of  Corti.  The  auditory  nerve  impulses  are 
conducted  through  the  cochlear  nerves  to  the  sensorium  where  they  produce 
auditory  sensations  with  the  same  definiteness  of  pattern  as  cutaneous  or 
optical  stimuli  produce  sensations  that  correspond  to  the  patterns  of  stimula- 
tion. The  audition  is  so  definite  that  one  can  consciously  pick  out  one  or 
the  other  of  the  constituent  stimulating  elements  and  follow  and  examine 
the  same  to  the  exclusion  of  the  others,  as  when  one  follows  a  single  instru- 
ment in  an  orchestra  or  a  single  voice  in  a  group  of  chattering  children. 

Bernstein  says  of  this  wonderful  organ: 

"  In  the  cochlea  we  have  to  do  with  a  series  of  apparatus  adapted  for  per- 
forming sympathetic  vibrations  with  wonderful  exactness.  We  have  here 
before  us  a  musical  instrument  which  is  designed,  not  to  create  musical 
sounds,  but  to  render  them  perceptible,  and  which  is  similar  in  construction 
to  artificial  musical  instruments,  but  which  far  surpasses  them  in  the  delicacy 
as  well  as  the  simplicity  of  its  execution.  For,  while  in  a  piano  every  string 
must  have  a  separate  hammer  by  means  of  which  it  is  sounded,  the  ear  pos- 
sesses a  single  hammer  of  an  ingenious  form  in  its  ear  bones,  which  can  make 
every  string  of  the  organ  of  Corti  sound  separately." 

Auditory  Judgments.  Direction.  The  power  of  perceiving  the 
direction  of  sounds  is  not  a  faculty  of  the  sense  of  hearing  itself,  but  is  an  act 
of  the  mind  judging  on  experience  previously  acquired.  From  the  modifica- 
tions which  the  sensation  of  sound  undergoes  according  to  the  direction  in 
which  the  sound  reaches  us,  the  mind  infers  the  position  of  the  sounding 
body.     The  only  true  guide  for  this  inference  is  the  more  intense  action  of  the 


AUDITORY    JUDGMENTS  027 

sound  upon  one  than  upon  the  other  ear.  But  even  here  there  is  room  for 
much  deception,  by  the  influence  of  reflexion  or  resonance,  and  by  the  propaga- 
tion of  sound  from  a  distance,  without  loss  of  intensity,  through  curved  con- 
ducting tubes  filled  with  air.  By  means  of  such  tubes,  or  of  solid  conductors, 
which  convey  the  sonorous  vibrations  from  their  source  to  a  distant  resonant 
body,  sounds  may  be  made  to  appear  to  originate  in  a  new  situation.  The 
direction  of  sound  may  also  be  judged  of  by  means  of  one  ear  only;  the  position 
of  the  ear  and  head  being  varied,  so  that  the  sonorous  undulations  at  one 
moment  fall  upon  the  ear  in  a  perpendicular  direction,  at  another  moment 
obliquely.  But  when  neither  of  these  circumstances  can  guide  us  in  dis- 
tinguishing the  direction  of  sound,  as  when  it  falls  equally  upon  both  ears, 
its  source  being,  for  example,  either  directly  in  front  or  behind  us,  it  becomes 
impossible  to  determine  whence  the  sound  comes. 

Distance.  The  judgment  of  the  distance  of  the  source  of  sounds  is  in- 
ferred from  their  intensity.  The  sound  is  interpreted  as  coming  from  an 
exterior  sonorous  body.  When  the  intensity  of  the  voice  is  modified  in  imita- 
tion of  the  effect  of  distance,  it  excites  the  idea  of  its  originating  at  a  distance 
Ventriloquists  take  advantage  of  the  difficulty  with  which  the  direction  of 
sound  is  recognized,  and  also  the  influence  of  the  imagination  over  our  judg- 
ment, when  they  modulate  the  voices,  and  at  the  same  time  pretend,  them- 
selves, to  hear  sounds  as  coming  from  a  certain  direction. 

Duration  0}  the  Auditory  Stimulus.  By  removing  one  or  several  teeth 
from  the  toothed  wheel  of  a  vibrator,  the  fact  has  been  demonstrated  that  in 
the  case  of  the  auditory  organ,  as  in  that  of  the  eye,  the  sensation  continues 
longer  than  the  impression  which  causes  it;  for  a  removal  of  the  tooth  pro- 
duced no  interruption  of  the  sound.  The  gradual  cessation  of  the  sensation 
of  sound  renders  it  difficult  to  determine  its  exact  duration  beyond  tha-t  of 
the  impression  of  the  sonorous  impulses. 

Binaural  Sensations.  Corresponding  to  the  double  vision  of  the  same 
object  with  the  two  eyes  is  the  double  hearing  with  the  two  ears;  and  analo- 
gous to  the  double  vision  with  one  eye,  dependent  on  unequal  refraction,  is 
the  double  hearing  of  a  single  sound  with  one  ear,  owing  to  the  sound  coming 
to  the  ear  through  media  of  unequal  conducting  power.  The  first  kind  of 
double  hearing  is  very  rare;  instances  of  it,  however,  have  been  recorded. 
The  second  kind,  which  depends  on  the  unequal  conducting  power  of  two 
media  through  which  the  same  sound  is  transmitted  to  the  ear,  may  easily 
be  experienced.  If  a  small  bell  be  sounded  in  water,  while  the  ears  are  closed 
by  plugs,  and  a  solid  conductor  be  interposed  between  the  water  and  one 
ear,  two  sounds  will  be  heard  differing  in  intensity  and  tone;  one  being  con- 
veyed to  the  ear  through  the  medium  of  the  atmosphere,  the  other  through 
the  conducting-rod. 

Subjective  Sensations.  Subjective  sounds  are  the  result  of  a  state  of  irri- 
tation or  excitement  of  the  auditory  nerve  produced  by  other  causes  than 


628  THE    SENSES 

sonorous  impulses.  A  state  of  excitement  of  this  nerve,  however  induced, 
gives  rise  to  the  sensation  of  sound.  Hence  the  ringing  and  buzzing  in  the 
ears  heard  by  persons  of  irritable  and  exhausted  nervous  system,  and  by 
patients  with  cerebral  disease,  or  disease  of  the  auditory  nerve  itself;  hence 
also  the  noise  in  the  ears  heard  for  some  time  after  a  long  journey  in  a  rattling, 
noisy  vehicle.  Ritter  found  that  electric  currents  also  excite  sounds  in  the 
ears.  From  the  above  truly  subjective  sound  we  must  distinguish  those 
dependent,  not  on  a  state  of  the  auditory  nerve  itself  merely,  but  on  sonorous 
vibrations  excited  in  the  auditory  apparatus.  Such  are  the  buzzing  sounds 
attendant  on  vascular  congestion  of  the  head  and  ear  or  on  aneurismal  dilata- 
tion of  the  vessels.  Frequently  even  the  simple  pulsatory  circulation  of  the 
blood  in  the  ear  is  heard.  To  the  sounds  of  this  class  belong  also  the  buzz 
or  hum,  heard  during  the  contraction  of  the  palatine  muscles  in  the  act  of  yawn- 
ing, during  the  forcing  of  air  into  the  tympanum  so  as  to  make  tense  the 
membrana  tympani. 

Irritation  or  excitement  of  the  auditory  nerve  is  capable  of  giving  rise  to 
movements  in  the  body  and  to  sensations  in  other  organs  of  sense.  In  both 
cases  it  is  probable  that  the  laws  of  reflex  action,  through  the  medium  of  the 
brain,  come  into  play.  An  intense  and  sudden  noise  excites,  in  every  person, 
closure  of  the  eyelids,  and,  in  nervous  individuals,  a  start  of  the  whole  body 
or  an  unpleasant  sensation  throughout  the  body  like  that  produced  by  an 
electric  shock. 

THE  SENSE  OF  EQUILIBRIUM. 

Although  the  utriculus,  sacculus,  and  semicircular  canals  form  the  major 
part  of  the  labyrinth  and  are  closely  associated  with  the  cochlea  in  develop- 
ment, there  is  increasing  evidence  that  these  structures  are  not  concerned 
with  hearing,  but  rather  with  a  sense  of  equilibrium.  This  view  has  been 
strengthened  by  recent  investigations  into  the  anatomical  relations  of  the 
different  elements  in  the  auditory  nerve,  figure  435. 

These  structures  have  each  a  special  modification  of  the  sensory  epithelium 
which  receives  the  vestibular  branch  of  the  eighth  nerve.  These  epithelial 
areas  are  differentiations  of  the  embryonic  ear  pit,  which  is  derived  from  the 
epiblast.  In  fishes  which  have  well-developed  semicircular  canals  and  vesti- 
bule, this  sensory  epithelium  has  a  common  origin  from  the  embryonic  anlage 
which  gives  rise  to  the  ear,  the  branchial  sense  organ,  and  the  lateral  line 
organs,  all  of  which  probably  have  static  functions. 

The  Semicircular  Canals.  The  semicircular  canals  are  connected 
with  the  utriculus,  are  three  in  number  on  each  side,  and  have  been  already 
shown  to  lie  in  space  practically  at  right  angles  to  one  another.  Each  is 
filled  with  endolymph,  and  each  has  a  special  organ,  the  crista  acustica, 
which  receives  a  division  of  the  vestibular  branch  of  the  eighth  nerve. 


THE    SEMICIRCULAR    CANALS  629 

The  function  of  the  semicircular  canals  is  believed  to  be  to  give  rise  to 
sensations  by  which  we  determine  the  motion  of  the  body  in  space.  It  was 
shown  long  ago  that  if  one  closes  his  eyes  and  turns  rapidly  around  the  vertical 
axis,  then  suddenly  stops  and  opens  the  eyes,  surrounding  objects  seem  to 
be  rotating  around  this  same  vertical  axis.  If  the  head  be  inclined  so  that 
the  face  is  in  the  horizontal  plane  and  the  rotation  around  the  vertical  axis 
be  repeated,  then,  upon  suddenly  raising  the  head  into  the  ordinary  position 
and  opening  the  eyes,  objects  seem  to  be  moving  about  the  head  around  the 
horizontal  axis.  In  both  these  cases  the  direction  of  the  apparent  motion 
of  objects  depends  upon  the  actual  motion  of  the  body  that  preceded  it  and 
is  in  the  opposite  direction.  In  the  first  case  the  rotation  is  in  the  plane  of 
the  horizontal  circular  canal.  It  is  assumed  here  that,  at  the  beginning  of 
such  a  movement,  the  endolymph,  being  fluid  and  inert,  tends  to  remain  still 
for  a  moment  and  the  canal  to  move  over  it  so  as  to  produce  pressure  in  the 
funnel  of  the  ampulla.  That  is,  it  has  the  same  effect  as  though  the  endo- 
lymph moved  in  the  canal.  This  relative  motion  bends  the  hairs  of  the  hair 
cells  of  the  crista  acustica,  thus  stimulating  the  hair  cells  and  giving  rise  to 
sensory  nerve  impulses.  When  the  head  suddenly  stops  rotating  the  situa- 
tion is  just  reversed  ?.nd  there  will  be  a  second  stimulation,  but  in  the  opposite 
direction.  When  one  considers  the  position  of  the  three  semicircular  canals, 
it  will  be  seen  that  movement  of  the  head  in  any  direction  will  stimulate  one 
or  more  of  the  cristae,  giving  rise  to  either  simple  or  complex  sensory  impulses. 

This  theory  is  borne  out  by  the  effects  of  operation  on  the  semicir- 
cular canals.  By  the  observations  of  Flourens,  injury  to  the  semicircular 
canals  causes  disturbances  in  muscular  coordination,  especially  in  move- 
ments that  take  place  in  the  plane  of  the  injured  canal.  If  a  horizontal  canal 
in  a  pigeon  be  sectioned,  the  animal  supports  its  head  in  the  vertical  position 
very  well,  but  is  unable  to  coordinate  its  horizontal  movements.  It  tends  to 
produce  rotary  motions  around  the  vertical  axis.  If  a  vertical  canal  is  sec- 
tioned, the  head  falls  to  one  or  the  other  side  according  to  the  canal,  and  the 
animal  shows  instability  of  position  in  that  plane.  It  has  been  shown  that 
stimulation  of  a  sectioned  canal  produced  reflex  movements  in  that  plane. 

Muscular  coordination  is  a  complex  phenomenon  and  involves  operation 
of  numerous  sensory  impulses  from  other  organs  of  the  body,  especially  from 
the  eye  and  general  skin.  Some  confusion  has  arisen  from  the  fact  that  there 
are  associated  with  the  disturbance  in  the  semicircular  canals  movements 
of  the  eyes  and  head  in  higher  animals,  and  of  the  eyes,  head,  and  fins  in  such 
animals  as  fishes — the  so-called  compensatory  movements.  Without  going 
into  details,  it  is  sufficient  to  state  that  the  sense  organs  of  the  semicircular 
canals  probably  form  only  one  of  the  series  of  sensory  structures  concerned 
in  the  coordination  of  movements. 

The  Utriculus  and  Sacculus.  The  utriculus  and  sacculus  each  have 
a  sensory    area,   the    macula?,    over  which    there    rests  in   the   human  ear 


030  THE     SENSES 

and  in  most  animals  small  particles  of  calcareous  matter,  otoliths.  These 
otoliths,  therefore,  lie  among  the  projecting  hairs  of  the  sensory  cells.  This 
is  characteristic  of  these  sensory  areas  and  differentiates  them  from  the 
arrangement  present  in  the  crista?.  There  would  seem  to  be  close  agree- 
ment in  function  between  the  maculae  and  cristae,  and  we  naturally  look  to 
the  influence  of  the  otoliths  on  the  processes  which  result  in  the  stimulation 
of  the  maculae.  Attempts  have  been  made  to  remove  the  otoliths,  with  the 
result  that  in  such  animals  there  Is  apparent  inability  to  maintain  a  constant 
position  in  space.  The  experiments  have  been  performed  which  have  sug- 
gested the  theory  that  the  otoliths  take  an  active  part  in  stimulating  the  sen- 
sory cells,  probably  by  their  mere  pressure.  If  the  head  is  inclined  in  one 
or  the  other  direction,  the  pressure  of  the  otoliths  will  shift  on  the  hair  cells, 
and  that  is  sufficient  to  stimulate  them.  If  this  view  is  correct,  then  we  may 
regard  these  structures  as  static  in  function  as  compared  with  the  semicircular 
canals,  which  are  dynamic.  The  anatomical  separation  of  the  nerves  for  the 
cochlea  from  the  division  for  the  utriculus,  sacculus,  and  semicircular  canals 
itself  suggests  isolation  in  function,  figures  389  and  435.  It  is  conceivable 
that  loud  noises  of  an  explosive  nature  may  cause  sufficient  vibration  of  the 
endolymph  to  affect  the  otoliths  and  thus  stimulate  the  cristae.  Yet,  if  such 
stimulation  takes  place  it  is  probably  only  of  secondary  importance. 


IV.  THE   SENSE  OF  SIGHT. 
THE  EYE. 

The  eye,  the  organ  of  vision,  is  the  most  complex  and  most  highly  devel- 
oped of  the  organs  of  special  sense.  It  consists  not  only  of  a  special  sen- 
sory epithelium,  the  retina,  sensitive  to  light  stimulation,  but  of  a  series  of 
special  structures  which  intensify  and  localize  the  stimulus.  There  are  also 
accessory  organs  for  the  protection  of  the  eye. 

The  Eyelids  and  Lachrymal  Apparatus.  The  eyeball  is  kept 
moist  over  its  free  surface  and  protected  from  external  injury  by  the  eyelids, 
by  the  glands  that  secrete  the  lachrymal  fluid  to  moisten  the  surface  of  the 
cornea,  and  by  the  oil  glands  that  secrete  oil  on  the  margins  of  the  lids. 

The  conjunctiva,  or  lining  membrane  of  the  lids,  which  is  reflected  on  to 
the  free  surface  of  the  eyeball,  protects  the  eye  from  injury  by  its  extraor- 
dinary sensitiveness  to  irritation  by  dust  or  other  external  substance.  Its 
stimulation  produces  reflex  secretion  of  the  lachrymal  fluid  that  flows  over 
the  surface  of  the  eye,  and  tends  to  wash  away  the  stimulating  substance. 

The  Eyeball  and  its  Parts.  The  detail  of  the  structure  of  the  eye- 
ball is  too  complex  to  be  given  here  except  in  so  far  as  seems  necessary  for  a 
clearer  presentation  of  the  physiological  facts.     A  gross  dissection  reveals 


THE    CORNEA 


631 


the  tough,  white,  sclerotic  coat;    the  intermediate  thin,  vascular,  pigmented 
choroid  coat;  and  the  inner  nervous  coat,  the  retina. 

The  section  also  shows  that  the  eyeball  is  specialized  in  structure  in  its 
anterior  region  and  that  its  contained  cavity  is  divided  into  two  parts,  viz., 


Canal  of  8ch]emra 
Suspensory  llga: 


Anterior  chamber 


Posterior  chamber 
Ciliary  process 
Canal  of  Petit 


Fig.   441. — Section  of  the  Eyeball. 

the  anterior  and  posterior  chambers  are  filled  with  the  transparent  aqueous 
fluid.  This  fluid  is  like  lymph  in  its  composition.  The  vitreous  chamber 
between  the  lens  and  the  retina  is  filled  with  the  clear  jelly-like  vitreous 
substance. 

The  Cornea.     The  sclerotic  coat  is  continuous  with  the  cornea  in 
front  of  the  eyeball,  but  the  cornea  is  transparent  and  its  radius  of  curvature 


Fig.  442. — Vertical  Section  of  Rabbit's  Cornea,  a,  Anterior  epithelium,  showing  the  different 
shapes  of  the  cells  at  various  depths  from  the  free  surface;  6,  portion  of  the  substance  of  cornea. 
(Klein.) 

is  less  than  that  of  the  main  portion  of  the  eye.  It  is  composed  of  strati- 
fied epithelial  cells,  and  is  richly  supplied  with  sensory  nerves  that  form 
an  intra -epithelial  plexus  of  delicate  varicose  fibrils.  The  cornea  has  no  blood- 
vessels, but  has  a  rich  network  of  lymphatic  spaces. 


632 


THE     SENSES 


The  Lens.  The  lens  is  a  special  modification  composed  of  highly 
refractive  material,  situated  just  behind  the  iris.  It  is  enclosed  in  a  capsule 
and  supported  in  its  place  by  the  suspensory  ligament,  which  is  fused  into 
the  capsule  around  its  equator.  The  lens  is  a  biconvex  structure  composed 
of  transparent  fibers  which  are  arranged  in  concentric  layers.  Its  posterior 
curvature  is  greater  than  the  anterior,  the  radii  being  6  and  10  mm.  respectively. 

The  Ciliary  Apparatus  and  the  Iris.  These  structures  are  a  con- 
tinuation and  modification  of  the  choroid  coat  in  the  anterior  portion  of  the 
eye.  Around  the  circumference  of  the  cornea  the  choroid  coat  is  consider- 
ably thickened  and  folded  in  the  modification  known  as  the  ciliary  apparatus. 
A  radial  layer  of  muscle,  figure  445,  is  knitted  into  the  base  of  the  cornea,  on 
the  one  hand,  and  extends  back  into  the  choroid,  on  the  other.  Thick  bundles 
of  the  circular  fibers  are  also  present  in  this  mass  of  muscle.     From  the  ciliary 


Fig.  443.  Fig.  444. 

Fig.  443. — Ciliary  Processes,  as  Seen  from  Behind,  i,  Posterior  surface  of  the  iris,  with  the 
sphincter  muscle  of  the  pupil;  2,  anterior  part  of  the  choroid  coat;  3,  one  of  the  ciliary  processes, 
of  which  about  seventy  are  represented.      X£. 

Fig.  444. — Laminated  Structure  of  the  Crystalline  Lens.  The  lamina?  are  split  up  after  hard- 
ening in  alcohol.  1,  The  denser  central  part  or  nucleus:  2,  the  successive  external  layers.  X4. 
(Arnold.) 


processes,  extending  over  the  lens,  is  the  iris.  It  is  a  sheet  of  connective  tissue 
and  muscle  lined  with  epithelium  and  highly  pigmented. 

In  the  middle  anterior  portion  is  a  round  aperture,  the  pupil.  The  mus- 
cle fibers  are  arranged  circularly  and  radially  and  are  of  the  unstriated  muscle 
type.  Contractions  of  the  circular  muscles  of  the  iris  produce  constriction 
of  the  pupil,  while  contractions  of  the  radial  fibers  produce  dilatation.  Both 
the  ciliary  apparatus  and  the  iris  are  supplied  with  motor  nerves. 

Fibers  of  the  third  cranial  nerve  are  distributed  to  the  ciliary  muscles, 
apparently  to  both  radial  and  circular  muscles,  and  when  these  nerves  are 
stimulating  the  resulting  contractions  of  the  muscles  tend  to  remove  the  tension 
from  the  capsule  of  the  lens.  These  nerve  fibers  pass  through  the  ciliary 
ganglion  where  they  form  a  synapsis  with  ganglionic  cells.  Motor  fibers 
from  the  third  cranial  nerve  also  supply  the  circular  muscles  of  the  iris,  which 
produce  constriction  of  the  pupil  through  the  motor  nerves  by  way  of  the 


STRUCTURE    OF    THE    RETINA 


633 


cervical  sympathetic  and  superior  cervical  ganglion,  and  the  ophthalmic  branch 
of  the  fifth  cranial  nerve. 

Structure  of  the  Retina.  The  retina  occupies  the  deeper  half  of  the 
cup  of  the  eyeball.  It  extends  forward  as  far  as  the  ora  serrata,  where  its 
complex  structure  changes  the  form  to  a  simple  epithelial  layer,  which  lines 
the  anterior  portion  of  the  eyeball  and  the  ciliary  processes.  In  the  center 
of  the  retina  is  a  round  yellowish  spot  having  a  minute  depression  in  its  center, 
called  the  yellow  spot  of  Sommering.     The  depression  in  its  center  is  the 


anterior  ciliary  arteries  and  veins 

greater  arterial  eircle 
angle  of  tbe  Iris 


ciliary  muscle 


Umbus  of  cornea 


anterior  chamber 


capsule  of  leus 


posterior  limiting  membrane 


\  stroma  of  iris 
posterior  surface  of  iris 
pbiucter  of  pupil 


Fig.  445. — Meridional  Section  of  a  Portion  of  the  Anterior  Part  of  the  Eyeball.     (Toldt.) 

fovea  centralis.  About  2.5  mm.  to  the  inner  side  of  the  yellow  spot  is  the 
point  at  which  the  optic  nerve  enters  and  spreads  out  its  fibers  into  the  retina. 
The  optic  nerve  arises  from  the  base  of  the  brain  and  passes  forward 
toward  the  orbit,  being  covered  by  the  membranes  which  cover  the  brain. 
The  fibers  of  the  optic  nerve  are  exceedingly  fine,  and  are  surrounded  by  the 
myelin  sheath,  but  do  not  possess  the  ordinary  external  nerve  sheath.  As 
they  pass  into  the  retina  they  lose  their  myelin  sheaths  and  proceed  as  axis- 
cylinders  (the  cells  of  origin  of  these  fibers  are  in  the  retina).  Neuroglia 
supports  the  nerve  fibers  in  the  optic  nerve  trunk.  In  the  center  of  the  nerve 
is  a  small  artery,  the  arteria  centralis  retincc.     The  number  of  fibers  in  the 


634 


THE     SENSES 


optic  nerve  is  said  to  be  upward  of  500,000.     The  fibers  of  the  optic  nerve 
spread  out  over  the  inner  surface  of  the  retina  as  far  as  the  ora  serrata. 

The  retina  itself  consists  of  layers  of  nerve  elements  supported  by  deli- 
cate connective  tissue.  The  older  descriptions  recognize  some  eight  or  ten 
layers  in  the  retina,  but  the  newer  investigations  of  Cajal,  Golgi,  Retzius, 
and  others  have  shown  that  the  retina  is  a  much  simpler  structure  than  hereto- 
fore described.     The  retina  is  formed  of  essentially  three  layers  of  nerve  cells. 


Stratum 
pigmenti 


Gangli- 
onic 
layer 

I  Stratum 
(opticuni 

Membrana  limitans  interna 


Fig.   446. — Section  of  Human  Retina.      (Cunningham,  modified  from  Schulze.) 

Naming  from  the  center  of  the  eye  outward,  they  are:  The  ganglionic  layer; 
the  layer  of  bipolar  cells;  and  the  layer  of  rods  and  cones,  figure  447.  The 
cells  of  these  layers  have  numerous  fibrous  processes  which  interlock  in  such  a 
way  that  they  seem  to  form  different  areas  when  studied  in  cross-section.  If 
we  recognize  the  strata  of  interlacing  fibers,  then  the  following  may  be 
made  out: 


The  layer  of  ganglion  cells. 
The  layer  of  bipolar  cells  .  . 


(  1.  Ganglionic  layer,  with  the  fibers  of  the  optic  nerve. 

)  2.  Internal  molecular  layer. 

1  3.   Internal  granular  layer. 

t  4.  The  external  molecular  layer. 


„,.  ,     .  (    v   The  external  granular  layer. 

1  he  laver  of  visual  cells {    <■    r^,      ,  c       ,  , 

0.    I  he  laver  of  rods  and  cones. 


STRUCTURE     OF    THE    RETINA 


635 


The  Nerve  Fiber  and  Nerve  Cell  Layers.  The  inside  of  the  retina  is 
formed  of  a  layer  of  nerve  fibers  which  have  their  origin  in  the  adjacent  large 
nerve  cells  and  run  toward  the  exit  of  the  optic  nerve.     Externally  the  gan- 


Fig.  447. — Transverse  Section  of  a  Mammalian  Retina.  A,  Layer  of  rods  and  cones;  B,  bodies 
of  visual  cells  (external  granular);  C,  external  molecular  layer;  E,  layer  of  bipolar  cells  (internal 
granular);  F,  internal  molecular  layer;  G,  layer  of  ganglionic  cells;  H,  layer  of  optic-nerve  fibers; 
a,  rod;  b,  cone;  c,  body  of  the  cone  cell;  J,  body  of  the  rod  cell;  e,  bipolar  rod  cells:  f,  bipolar  cone 
cells;  g,  h,' i,  j,  k,  ganglionic  cells  ramifying  in  the  various  strata  of  the  internal  molecular  zone; 
r,  inferior  arborization  of  the  bipolar  rod  cells,  connecting  with  the  ganglionic  cells;  r,  inferior 
arborization  of  the  bipolar  cone  cells;  t,  epithelial  or  Miiller  cells;  x,  point  of  contact  between  the 
rods  and  their  bipolar  cells;  g,  point  of  contact  between  the  cones  and  their  bipolar  cells;  5,  centrif- 
ugal nerve  fiber.      (Cajal.) 

glionic  cells  send  up  numerous  processes,  or  dendrites,  which  interlace  with 
the  fibers  of  the  bipolar  cells  of  the  second  layer. 

The  Middle  Layer.     The  middle  layer  consists  of  bipolar  cells  which  send 
one  process  toward  the  ganglionic  layer  to  interlace  with  the  dendrites  of  the 


Fig.  448. — Perpendicular  Section  of  the  Retina  of  a  Mammal.  A.  External  grains  or  bodies  of 
rods;  B,  bodies  of  cones;  a,  horizontal  external  or  small  cell;  6,  horizontal  internal  or  large  cell;  c, 
horizontal  internal  cell  with  descending  protoplasmic  appendages;  e,  flattened  arborization  of  one 
of  the  large  cells;  f.  g,  h,  j,  I,  spongioblasts  ramifying  in  the  various  strata  of  the  internal  molec- 
uiarzone;  m,  n,  diffuse  spongioblasts;  o,  ganglionic  cell;  1,  external  molecular  zone;  2,  internal 
molecular  zone.     (Cajal.) 


636 


THE    SENSES 


ganglionic  cells,  and  one  process  externally.  This  process  is  often  divided 
into  many  branches,  which  separate  out  into  a  horizontal  brush,  interlacing 
with  the  processes  of  the  rods  and  cones.  Special  cells  have  been  described 
for  this  layer  of  the  retina,  as,  for  example,  the  spongioblasts  of  Cajal. 

The  External  Layer  0}  Rods  and  Cones.  The  rod  cells  are  composed  of 
two  parts  quite  different  in  structure,  known  as  the  outer  and  inner  limbs. 
The  outer  limb  is  a  cylindrical  rod  about  30  /-/.  long  by  2  ;>-  in  diameter.  It  is 
transparent  and  composed  of  doubly  refractive  material.  The  inner  limb 
of  the  cell  is  about  the  same  length  as  the  outer,  is  similar,  and  is  longitudinally 
striated,  and  contains  a  nucleus  on  its  course,  figure  447,  d. 

The  cone  cells  are  also  made  up  of  two  limbs,  the  outer  of  which  is  conical 
instead  of  cylindrical  as  in  the  case  of  the  rods.  In  other  respects  they  are 
similar  to  the  rods  in  structure,  with  the  exception  that  the  inner  limb  ends 
in  a  brush  of  fibrils  which  interlace  with  the  bipolar  cells  of  the  middle  layer. 


Fig.  449.- 


-Distribution  of  the  Rods  and  Cones.     A,  In  the  peripheral  part  of  the  retina; 
B,  from  the  region  of  the  macula  lutea. 


In  man  and  mammals  the  number  of  rod  cells  are  much  greater  than  the  cones, 
but  it  is  said  that  in  birds  cones  predominate.  Even  in  man  the  center  of  the 
fovea  centralis  is  devoid  of  rods  and  consists  of  cones  only,  figure  450. 

All  the  elements  of  the  retina  are  sustained  and  isolated  by  large  cells 
lying  vertically  which  are  known  as  the  fibers  of  Mutter.  The  nucleus  of  the 
fiber  of  Miiller  is  found  at  the  level  of  the  internal  granular  layer,  and  the 
two  extremities  of  the  protoplasm  or  cell  body  are  condensed  in  two  homo- 
geneous layers,  known  as  the  external  and  the  internal  limiting  layer.  The 
external  limiting  layer  is  placed  just  between  the  two  segments  of  the  rod 
and  cone  cells.  The  internal  limiting  layer  is  situated  upon  the  internal 
surface  of  the  retina. 

At  the  ora  serrata  the  layers  are  not  perfect  and  disappear  in  this  order: 
nerve  fibers  and  ganglion  cells,  then  the  rods,  leaving  only  the  inner  limbs  of 
the  cones,  these  cease,  then  the  inner  molecular  layer.  The  Miillerian  fibers 
persist. 


STRUCTURE    OF    THE    RETINA 


637 


At  the  pars  ciliaris  retinae,  the  retina 
is  represented  by  a  layer  of  columnar 
cells,  derived  from  the  fusion  of  the 
nuclear  layers  which  are  in  contact  with 
the  pigment  layers  of  the  retina  and  con- 
tinued over  the  ciliary  processes. 

Pigment  Layer.  This  layer,  which 
was  formerly  considered  part  of  the 
choroid,  consists  of  cells  which  cover 
and  entirely  surround  the  outer  limbs 
of  the  rods  and  cones. 

Blood-vessels  of  the  Eyeball.  The 
eye  is  very  richly  supplied  with  blood- 
vessels. In  addition  to  the  conjunc- 
tival vessels,  which  are  derived  from  the 
palpebral  and  lachrymal  arteries,  there 
are  at  least  two  other  distinct  sets 
of  vessels  supplying  the  tunics  of  the 
eyeball,  i,  The  vessels  of  the  sclerotic, 
choroid,  and  iris,  and  2,  the  vessels  of 
the  retina.  The  first  are  the  short  and 
long  posterior  ciliary  arteries  which 
pierce  the  sclerotic  in  the  posterior  half 
of  the  eyeball,  and  the  anterior  ciliary 
which  enter  near  the  insertions  of  the 
recti.  These  vessels  anastomose  and 
form  a  very  rich  choroidal  plexus; 
they  also  supply  the  iris  and  ciliary 
processes,  forming  a  very  highly  vas- 
cular circle  round  the  outer  margin 
of  the  iris  and  adjoining  portion  of 
the  sclerotic.  The  distinctness  of 
these  vessels  from  those  of  the  con- 
junctiva is  well  seen  in  the  difference 
between  the  bright  red  of  blood-shot 
eyes  (conjunctival  congestion),  and  the 
pink  zone  surrounding  the  cornea 
which  indicates  deep-seated  ciliary  con- 
gestion. 

The  central  artery  of  the  optic  nerve 
enters  the  retina  from  the  center  of 
the  optic  disc  and  sends  out  branches 
over  the  retinal  cup  lying  in  the  nerve 


Fig.  450. — Diagrammatic  Section  of  the 
Macula  Lutea  and  Fovea  Centralis.  2, 
Layer  of  nerve  fibers;  3,  layer  of  multi- 
polar cells;  4,  internal  molecular  layer, 
composed  of  intertwining  arborescent  proc- 
esses; 5,  layer  of  bipolar  cells,  or  internal 
granular  layer;  6,  external  molecular  layer, 
composed  of  intertwining  arborescent  proc- 
esses: 7,  nuclei  of  epithelial  cells,  or  ex- 
ernal  granular  layer;  8,  frillwork  formed 
by  processes  from  fibers  of  Miiller,  often 
called  the  "external  limiting  membrane"; 
9,  layer  of  rods  and  cones;  10,  layer  of 
pigment  epithelium. 


038 


THE     SENSES 


fiber  layer,  figure  451.     These  blood-vessels,  however,  are  absent  from  the 
fovea  centralis  and  reduced  in  size  in  the  macula  lutea,  figures  451  and  452. 


Fig.  451. — Diagram  of  the  Blood-vessels  of  the  Human  Retina.  (Leber,  after  Jaeger.)  ans, 
vns,  Superior  nasal  artery  and  vein;  ats,  vts,  superior  temporal  artery  and  vein;  ani,  vni,  inferior 
nasal  artery  and  vein;  ati,  vti,  inferior  temporal  artery  and  vein;  am,  vm,  macular  artery  and  vein; 
ane,  vnie,  median  artery  and  vein. 


Fig.   452. — Blood-vessels  of  the  Macula  Lutea.     The  part  that  is  totally  free  from  vessels  is 

the  fovea  centralis. 


THE  OPTICAL  APPARATUS. 

The  optical  apparatus  may  be  supposed,  for  the  sake  of  description,  to 
consist  of  several  parts;  1,  A  system  of  transparent  refracting  surfaces  and 
media  by  means  of  which  images  of  external  objects  are  brought  to  a  focus 
upon  the  back  of  the  eye;  2,  a  sensitive  screen,  the  retina,  which  is  a  special- 
ized sensory  apparatus  in  connection  with  the  terminations  of  the  optic  nerve, 
and  capable  of  being  stimulated  by  luminous  objects,  and  of  sending  such 
impressions  as  to  produce  in  the  brain  visual  sensations.     To  these  main 


REFRACTIVE  MEDIA  AND  SURFACES  039 

parts  may  be  added,  3,  an  apparatus  for  focussing  light  from  objects  at  differ- 
ent distances  from  the  eye;  and  4,  since  both  eyes  are  usually  employed  in 
vision,  an  arrangement  by  means  of  which  the  eyes  may  be  turned  in  the 
same  direction  so  that  binocular  vision  is  possible.  The  arrangement  of 
the  optic  nerve  fibers,  and  of  the  continuation  of  these  backward  in  the  optic 
chiasma,  and  thence  to  special  districts  of  the  brain  have  already  been  dis- 
cussed. 

The  eye  may  be  compared  to  a  photographic  camera,  and  the  transparent 
refracting  media  correspond  to  the  photographic  lens.  In  a  camera  images 
of  external  objects  are  thrown  upon  a  screen,  the  sensitive  plate,  at  the  back 
of  the  camera  box.  In  the  eye,  the  camera  proper  is  represented  by  the  eye- 
ball with  its  choroidal  pigment,  the  sensitive  screen  by  the  retina,  and  the 
lens  by  the  refracting  media.  In  the  case  of  the  camera,  the  screen  is  adjusted 
to  receive  clear  images  of  objects  at  different  distances  by  an  apparatus  for 
focussing.  The  corresponding  adjustment  in  the  eye  is  accomplished  by 
the  accommodating  apparatus. 

Refractive  Media  and  Surfaces.  At  first  sight  it  would  seem  as  if 
the  refracting  apparatus  of  the  eye  were  very  complicated,  since  it  consists 
of  so  many  parts.  These  parts  are:  the  anterior  surface  of  the  cornea  itself, 
the  posterior  surface  of  the  cornea,  the  aqueous  humor,  the  anterior  surface 
of  the  lens,  the  substance  of  the  lens  itself  (which  is  unequally  refractive), 
the  posterior  surface  of  the  lens,  and  the  vitreous  humor.  Thus  there  are 
four  surfaces,  and  at  least,  including  the  air,  five  media.  For  all  practical 
purposes,  however,  we  may  leave  out  of  consideration  all  but  three  refracting 
surfaces  and  their  adjacent  media.  These  are:  the  anterior  surface  of  the 
cornea,  separating  the  air  and  the  corneal  substance;  the  anterior  surface 
of  the  lens,  separating  the  aqueous  humor  and  the  lens  substance;  and  the 
posterior  surface  of  the  lens,  separating  the  lens  surface  from  the  vitreous 
humor. 

Image  Formation.  In  the  refraction  through  a  simple  transparent 
spherical  surface  there  are  certain  cardinal  points  to  be  considered.  The 
rays  of  light  which  fall  perpendicularly  on  such  a  surface  pass  through  with- 
out refraction.  All  such  rays  cut  the  center  of  the  radius  of  curvature  of  the 
lens,  called  the  nodal  point.  A  line  that  passes  through  the  center  of  curva- 
ture of  a  lens  and  thus  pierces  the  nodal  point  is  called  the  optical  axis,  and 
the  point  on  the  surface  pierced  by  the  optical  axis  is  the  principal  point. 
In  every  optical  system  there  are  certain  other  cardinal  facts  to  be  considered. 
All  rays  which  do  not  strike  vertical  to  the  curved  surface  are  refracted 
toward  the  optical  axis.  Rays  which  impinge  upon  the  spherical  surface  of 
a  lens  parallel  to  the  optical  axis  will  meet  at  a  point  upon  the  axis  called  the 
posterior  principal  focus,  figure  453,  F.  The  posterior  principal  focus  is 
outside  of  the  nodal  point.  Again,  there  is  a  point  in  the  optical  axis  in  front 
of  the  surface,  rays  of  light  from  which  strike  the  surface  so  that  they  are 


G40 


THE    SENSES 


refracted  in  a  line  parallel  with  the  axis,  dj";  such  a   point,  F2,  is  called  the 
anterior  principal  focus. 

In  any  given  system  the  principal  foci  can  be  found  by  erecting  verticals 
at  the  nodal  and  principal  points  of  the  optical  axis  and  laying  off  lengths 
on  each,  a  and  b,  proportional  to  the  refractive  indices  of  the  media.  A  line 
drawn  through  a  on  the  principal  vertical  and  b  on  the  nodal  vertical  will  cut 
the  optical  axis  at  the  posterior  principal  focus,  and  vice  versa. 


Fig.  453. — Diagram  of  a  Simple  Optical  System.  (Foster.)  The  curved  surface,  bd,  is  sup- 
posed to  separate  a  less  refractive  medium  toward  the  left  from  a  more  refractive  medium  toward 
the  right. 

If  a  luminous  point  outside  the  anterior  principal  focus  is  considered, 
it  is  obvious  that  rays  from  it  will  be  so  refracted  when  they  enter  the  convex 
surface  that  they  will  become  converging  and  will  ultimately  meet  again  in 
a  point  or  focus.  Two  such  points  form  conjugate  foci,  figure  454.  If  the 
anterior  focus  of  a  conjugate  is  moved  away  from  the  anterior  principal  focus, 
then  the  posterior  conjugate  will  move  toward  the  posterior  principal  focus, 
and  the  converse.     If  one  conjugate  is  known,  the  other  can  be  found  as 


Fig.   454- — Diagram  to  Show  the  Relations  of  Conjugate  Foci,     cd.  Refracting  surface;  AB 
and  ba,  conjugate  foci;    o,  nodal  point;    F",  posterior  principal  focus. 


follows:  From  a  point  in  the  plane  of  the  known  conjugate,  but  outside  the 
principal  axis,  draw  two  rays,  one  perpendicular  to  the  refracting  surface 
which  will  pass  through  the  nodal  point,  the  other  parallel  to  the  principal 
axis.  The  latter  will  be  refracted  through  the  posterior  principal  focus  and 
when  prolonged  will  meet  the  first  ray  in  the  plane  of  the  second  conjugate, 
figure  454,  a.  This  relationship  between  conjugate  foci  is  played  upon  in  the 
focussing  of  a  camera. 


IMAGE    FORMATION  641 

It  is  quite  obvious  that  the  eye,  even  considering  only  the  three  surfaces 
above  indicated,  is  a  much  more  complicated  optical  apparatus  than  the  one 
described  in  the  figure.  It  is,  however,  possible  to  reduce  the  refractive 
surfaces  and  media  to  a  simpler  form  when  the  refractive  indices  of  the  dif- 
ferent media  and  the  curvature  of  each  surface  are  known.  All  of  these 
data  have  been  very  carefully  collected.     They  are  as  follows: 

Index  of  refraction  of  aqueous  and  vitreous,  .  .  .  .  .    =  1.3365 

"   the  lens,      .......=  1.4371 

Radius  of  curvature  of  cornea,      .......=  7-829  mm. 

"  "  "  anterior  surface  of  lens,       .  .  .  .    =  10.0 

"  "   posterior     "  .    =  6.0 

Distance  from  anterior  surface  of  cornea  and  anterior  surface  of  lens,    =  3.6 

Distance  from  posterior  surface  of  cornea  and  posterior  surface  of  lens,    =  7.2 

With  these  data  it  has  been  found  comparatively  easy  by  mathematical 
calculation  to  reduce  the  different  refractive  surfaces  of  the  different  curva- 
tures into  one  mean  curved  surface  of  known  curvature,  and  the  differently 
refracting  media  into  one  mean  medium  the  refractive  power  of  which  is 
known. 

The  simplified  or  so-called  schematic  eye,  formed  upon  this  principle, 
suggested  by  Listing  as  the  reduced  eye,  has  the  following  dimensions: 


From  the  anterior  surface  of  the"  cornea  to  the  principal  point, 
From  the  nodal  point  to  the  posterior  surface  of  lens, 
Posterior  chief   focus  lies  behind  cornea, 
Anterior  chief  focus  in  front  of  cornea, 
Radius  of  curvature  of  ideal  surface,      . 


=        2.3448  mm 
=        0.4764     " 

=  22.8237     " 

=  12.8326     " 
=        5.1248     " 


In  this  reduced  or  simplified  eye  the  principal  posterior  focus,  about 
23  mm.  behind  the  spherical  surface,  would  correspond  to  the  position  of 
the  retina  behind  the  anterior  surface  of  the  cornea.  The  refracting  surface 
would  be  situated  about  midway  between  the  posterior  surface  of  the  cornea 
and  the  anterior  surface  of  the  lens. 

The  optical  axis  of  the  eye  is  a  line  drawn  through  the  centers  of  curva- 
ture of  the  cornea  and  lens,  and  when  prolonged  backward  it  cuts  the  retina 
between  the  optic  disc  and  the  fovea  centralis.  This  differs  somewhat  from 
the  visual  axis  which  passes  through  the  nodal  point  of  the  reduced  eye  to 
the  fovea  centralis,  and  forms  an  angle  of  five  degrees  with  the  optical  axis. 
The  visual  or  optical  angle  is  the  angle  included  between  the  lines  drawn 
from  the  borders  of  any  object  through  the  nodal  point.  It  has  been  shown 
by  Helmholtz  that  the  smallest  angular  distance  between  two  points  which 
can  be  appreciated  is  fifty  seconds,  the  size  of  the  retinal  image  being  3.65  p.; 
this  practically  corresponds  to  the  diameter  of  the  cones  at  the  fovea  centralis 
which  is  3  fi,  the  distance  between  the  centers  of  two  adjacent  cones  being  4  fi. 

The  image  of  an  object  formed  upon  the  retina  may  be  considered  as  a 
series  of  points,  from  each  of  which  a  pencil  of  light  diverges  to  the  eye,  and 
41 


642 


THE     SENSES 


this  pencil  has  for  its  center  or  axis  a  ray  which  impinging  upon  the  refrac- 
tive surface  perpendicularly  to  the  surface  is  not  refracted,  but  passes  through 
the  nodal  point  and  is  prolonged  backward  to  the  retina,  whereas  the  diverging 
rays  are  also  made  to  converge  to  a  principal  posterior  focus  behind  the  lens, 


Fig.   455- — Diagram  of  the  Method  of  the  Formation  of  an  Inverted  Image  Exactly  Focussed 
upon  the  Retina.     The  dotted  line  is  the  ideal  surface  of  curvature. 

or  the  chief  axis  of  the  pencil  of  light  proceeding  from  the  point  in  question, 
and  this  focus,  if  the  image  is  to  be  clear,  should  fall  on  the  retina. 

Thus  from  each  point  of  an  object  a  corresponding  image  is  formed  on 
the  retina,  so  that  an  image  of  the  distant  object  is  produced.  It  is  an  inverted 
image.  Whether  the  image  is  blurred  or  not  depends  upon  the  refractive 
power  of  the  media,  and  upon  the  distance  of  the  anterior  surface  of  the  cornea 
from  the  retina.  If  the  refractive  media  are  too  powerful,  or  the  eye  too  long, 
the  image  is  formed  in  front  of  the  retina,  figure  456;  if  the  reverse,  the  image 


Fig.  456. — Diagram  of  the  Course  of  a  Ray  of  Light,  to  Show  how  a  Blurred  or  Indistinct  Image 
is  Formed  if  the  Object  be  not  Exactly  Focussed  upon  Retina.  The  surface  CC  should  be  supposed 
to  represent  the  ideal  curvature.  The  nodal  point  should  be  nearer  the  posterior  surface  of  lens 
as  in  figure  4SS- 


is  formed  behind  the  retina,  and  in  both  cases  an  indistinct  and  blurred  image 
is  the  result. 

Accommodation.  The  distinctness  of  the  image  formed  upon  the 
retina  is  mainly  dependent  on  the  perfection  with  which  the  rays  emitted 
by  each  luminous  point  of  the  object  are  brought  to  a  focus  upon  the  retina. 


ACCOMMODATION  643 

If  this  focus  occurs  at  a  point  either  in  front  of  or  behind  the  retina,  indis- 
tinctness of  vision  ensues,  in  the  way  we  have  just  described,  with  the  pro- 
duction of  a  halo.  The  jocal  distance,  i.e.,  the  distance  of  the  point  at 
which  the  luminous  rays  are  collected  from  a  lens,  besides  being  regulated 
by  the  degree  of  convexity  and  density  of  the  lens,  varies  with  the  distance 
of  the  object  from  the  lens,  being  greater  as  this  is  shorter,  and  vice  versa. 
In  other  words,  the  luminous  points  on  the  object  and  the  focal  points  on  the 
retina  are  conjugate  foci.  Hence,  since  objects  placed  at  various  distances 
from  the  eye  can  within  certain  limits  be  seen  with  almost  equal  distinctness, 
there  must  be  some  provision  by  which  the  eye  is  enabled  to  adapt  itself,  so 
that,  at  whatever  distance  the  luminous  object  may  be,  the  focal  point  may 
always  fall  exactly  upon  the  retina. 

Accommodation  is  the  act  of  adapting  the  eye  to  vision  at  different  distances. 
It  is  obvious  that  the  effect  might  be  produced  in  either  of  two  ways,  viz., 
i,  by  altering  the  convexity,  and  thus  the  re- 
fracting power,  either  of  the  cornea  or  of  the 
lens;  or  2,  by  changing  the  position  of  the 
lens  relative  to  the  retina,  as  in  the  focussing 
of  a  camera,  so  that  whether  the  object  be 
near  or  distant,  the  focal  points  to  which  the 
rays  are  converged  by  the  -lens  may  always 
fall  exactly  on  the  retina.  The  amount  of 
either  of  these  changes  which  is  required 
in  even   the  widest  range  of  vision  is    ex-        Tt£I%4fl777Diag?mV  SiV?wins 

o  Inree  Reflections  of  a  Candle,    i, 

tremely  small,  for  from  the  refractive  powers        !"rom  thf  ante^or  surface  of  cor- 

J  "  nea;    2,  from  the  anterior  surface 

of  the  media  of  the  eye  the  difference   be-        i&W 1^*?faSSSE 
tween    the    focal   distances    of  the   images        pianation  see  text.    Theexperi- 

o"^  ment  is   best   performed   by  em- 

of  an  object  at  a  distance  and  of  one   at        gfflXjtSSffpwEH*? 
four   inches    is    only  about   3.5    mm.     On 

this  calculation  the  change  in  the  distance  of  the  retina  from  the  lens  re- 
quired for  vision  at  all  distances,  supposing  the  cornea  and  lens  to  remain 
the  same,  would  not  be  more  than  about  one  line.  Beer  has  shown  that  the 
second  method  is  indeed  the  type  of  accommodative  apparatus  in  fishes. 
But  in  man  and  the  higher  animals  accommodation  occurs  by  the  first 
method,  i.e.,  by  changing  the  convexity  of  the  refracting  surface. 

The  accommodation  of  the  human  eve  for  objects  at  different  distances  is 
primarily  due  to  a  varying  shape  of  the  lens,  its  front  surface  becoming  more 
or  less  convex,  according  as  the  distance  of  the  object  looked  at  is  near  or 
far.  The  nearer  the  object,  the  more  convex  the  front  surface  of  the  lens, 
up  to  a  certain  limit,  and  vice  versa ;  the  back  surface  takes  little  or  no  share 
in  accommodation.  The  following  simple  experiment  illustrates  this  point: 
If  a  lighted  candle  be  held  a  little  to  one  side  of  a  person's  eye,  an  observer 
looking  at  the  eye  from  the  other  side  sees  three  distinct  images  of  the  flame, 


644 


THE    SENSES 


figure  457.  The  first  and  brightest  is,  i,  a  small  erect  image  formed  by  the 
anterior  convex  surface  of  the  cornea;  the  second,  2,  is  also  erect,  but  larger 
and  less  distinct  than  the  preceding,  and  is  formed  at  the  anterior  convex 
surface  of  the  lens;  the  third,  3,  is  smaller,  inverted,  and  indistinct;  it  is 
formed  at  the  posterior  surface  of  the  lens,  which  is  concave  forward,  and 


Fig.  459. 

Fig.  458. — Diagram  of  Sanson's  Images.  A,  When  the  eyes  are  focussed  for  far  objects,  and 
B,  when  they  are  focussed  for  near  objects.  The  figure  to  the  right  in  .4  and  B  is  the  inverted 
image  from  the  posterior  surface  of  the  lens. 

Fig.  459. — Phakoscope  of  Helmholtz.  At  B,  B' ,  are  two  prisms,  by  which  the  light  of  a  candle 
is  concentrated  on  the  eye  of  the  person  experimented  with  at  C,  A  is  the  aperture  for  the  eye 
of  the  observer.  The  observer  notices  three  double  images,  as  in  figures  457  and  458,  reflected  from 
the  eye  under  examination  when  the  eye  is  fixed  upon  a  distant  object;  the  position  of  the  images 
having  been  noticed,  the  observed  eye  is  then  focussed  on  a  near  object,  such  as  a  reed  pushed  up 
by  C;  the  images  from  the  anterior  surface  of  the  lens  will  be  observed  to  move  toward  each  other, 
in  consequence  of  the  lens  becoming  more  convex. 


therefore,  like  all  concave  mirrors,  gives  an  inverted  image.  If  now  the  eye 
under  observation  be  made  to  look  at  a  near  object,  the  second  image  be- 
comes smaller,  clearer,  and  approaches  the  first.  If  the  eye  be  now  adjusted 
for  a  far  point,  the  second  image  enlarges  again,  becomes  less  distinct,  and 
recedes  from  the  first.  In  both  cases  alike  the  first  and  third  images  remain 
unaltered  in  size,  distinctness,  and  relative  position.  This  proves  that  during 
accommodation  for  near  objects  the  curvature  of  the  cornea,  and  that  of  the 
posterior  surface  of  the  lens,  remain  unaltered,  while  the  anterior  surface  of 
the  lens  becomes  more  convex  and  approaches  the  cornea. 

The  experiment,  figure  458,  is  more  striking  when  the  two  prisms  of  the 
phakoscope  which  form  two  images  of  the  candle  are  used.  The  pair  of 
images  of  the  candle  from  the  front  surface  of  the  lens  not  only  approach 
those  from  the  cornea  during  accommodation,  but  also  approach  one  another, 
and  become  somewhat  smaller,  Sanson's  images. 


THE    MECHANISM    OF    ACCOMMODATION 


645 


The  Mechanism  of  Accommodation.  The  mechanism  of  accommo- 
dation depends  primarily  upon  the  inherent  tendency  of  the  lens  to  approxi- 
mate the  shape  of  a  sphere.  When  the  eye  is  at  rest  the  intra -ocular  tension 
is  such  as  to  put  stress  on  the  suspensory  ligament  around  its  equator,  which 
compresses  the  elastic  lens  in  its  antero-posterior  dimension.  The  elasticity 
of  the  lens  can  make  itself  apparent  when  the  tension  of  the  suspensory  liga- 
ment is  relaxed.  This  takes  place  completely  after  a  division  of  the  fibers 
of  the  zonula.  When  we  remove  the  lens  from  the  eye  of  a  young  person, 
we  see  it  assume  the  spherical  shape  immediately  upon  the  division  of  its 
connections.  In  life  this  slackening  of  the  tension  of  the  suspensory  liga- 
ment of  the  lens  is  brought  about  by  the  contraction  of  the  fibers  of  the  ciliary 
body.  This  allows  the  anterior  surface  of  the  lens  to  become  more  convex, 
by  its  own  elastic  powers,  thus  focussing  entering  rays  of  light  from  a  near 
object  upon  the  retina,  figure  460.  It  therefore  appears  that  when  the  eye 
is  at  rest  it  is  focussed  for  distant  objects,  inasmuch  as  the  suspensory  liga- 
ment is  taut  and  the  anterior  surface  of  the  lens  more  flattened.  The  normal 
eye  is  passive  when  in  focus  for  distant  objects.  It  is  the  active  contraction 
of  the  muscles  of  accommodation  that  focusses  for  near  objects.  The  iris 
acts  in  coordination  with  the  accommodative  contractions  of  the  ciliary  mus- 
cles. In  viewing  near  objects  the  pupil  contracts,  and  upon  viewing  distant 
ones  it  dilates. 

Range  of  Distinct  Vision.  Near-point.  In  every  eye  there  is  a  limit  to 
the  power  of  accommodation.     If  a  book  be  brought  nearer  and  nearer  to  the 


Fig.  460. 


-Diagram  Representing  by  Dotted  Lines  the  Alteration  in  the  Shape  of  the  Lens  on 
Accommodation  for  Near  Objects.     (E.  Landolt.) 


eve,  the  type  at  last  becomes  indistinct,  and  cannot  be  brought  into  focus 
by  any  effort  of  accommodation,  however  strong.  This  limit,  which  is  termed 
the  near-point,  can  be  determined  by  the  experiment  of  Scheiner.  Two 
small  holes  not  more  than  2  mm.  apart  are  pricked  in  a  card  with  a  pin;  at 
any  rate  their  distance  from  each  other  must  not  exceed  the  diameter  of  the 
pupil.     The  card  is  held  close  in  front  of  the  eye,  and  a  small  needle  viewed 


646 


THE    SENSES 


through  the  pin-holes.  At  a  moderate  distance  it  can  be  clearly  focussed, 
but  when  brought  nearer,  beyond  a  certain  point,  the  image  appears  double 
and  more  or  less  blurred.  This  point  where  the  needle  ceases  to  appear  single 
is  the  near-point  of  vision.     Its  distance  from  the  eye  can  of  course  be  readily 


Fig.  461. — Diagram  of  Experiment  to  Ascertain  the  Minimum  Distance  of  Distinct  Vision. 

measured.  It  is  usually  about  five  or  six  inches,  12  to  15  cm.  In  the  accom- 
panying figure,  461,  the  lens  b  represents  the  eye;  e,  /,  the  two  pin-holes  in  the 
card,  nn  the  retina ;  a  represents  the  position  of  the  needle.  When  the  needle 
is  at  a  moderate  distance,  the  two  pencils  of  light  coming  from  e  and  /  are 
focussed  at  a  single  point  on  the  retina  nn.     If  the  needle  be  brought  nearer 


Fig.  462. — Diagram  of  the  Axes  of  Rotation  of  the  Eye.     The  thin  lines  indicate  axes  of 
rotation,  the  thick  the  position  of  muscular  attachment. 

than  the  near-point,  the  strongest  effort  of  accommodation  is  not  sufficient 
to  focus  the  two  pencils,  they  meet  at  a  point  behind  the  retina.  The  effect 
is  the  same  as  if  the  retina  were  shifted  forward  to  mm.  Two  images  h,  g,  are 
formed,  one  from  each  hole.     It  is  interesting  to  note  that  when  in  this  way 


REFLEXES     OF    THE     PUPIL 


647 


two  images  are  produced,  the  lower  one  g  really  appears  in  the  position  Q, 
while  the  upper  one  appears  in  the  position  P.  This  may  be  readily  verified 
by  covering  the  holes  in  succession. 

During  accommodation  two  other  changes  take  place  in  the  eyes.  The 
eyes  converge  by  the  action  of  the  extra-ocular  muscles,  chiefly  by  the  internal 
and  inferior  recti  or  internal  and  superior  recti.     The  pupils  contract. 

Movements  of  the  Eye.  The  eyeball  possesses  movement  around  three  axes  indicated 
in  figure  462,  viz.,  an  antero-posterior,  a  vertical,  and  a  transverse,  passing  through  a 
center  of  rotation  a  little  behind  the  centre  of  the  optic  axis.  The  movements  are  ac- 
complished by  pairs  of  muscles. 


Direction  of  Movement. 
Inward,  .... 

Outward,         .... 

Upward,  .... 

Downward,     .... 
Inward  and  upward, 
Inward  and  downward,    . 
Outward  and  upward, 
Outward  and  downward, 


By  what  muscles  accomplished. 

Internal  rectus. 

External  rectus. 
(  Superior  rectus. 
\  Inferior  oblique. 
(  Inferior  rectus. 
I  Superior  oblique. 

{Internal  and  superior  rectus. 
Inferior  oblique. 
I  Internal  and  inferior  rectus. 
(  Superior  oblique, 
j  External  and  superior  rectus. 
\  Inferior  oblique. 
1  External  and  inferior  rectus. 
(  Superior  oblique. 


The  contraction  of  all  of  the  muscles  during  the  act  of  accommodation,  viz., 
of  the  ciliary  muscle,  of  the  recti  muscles,  and  of  the  sphincter  pupillae,  is 
under  the  control  of  the  fibers  of  the  third  nerve.  But  the  superior  oblique 
may  also  be  employed,  in  which  case  the  fourth  nerve  is  concerned. 

Reflexes  of  the  Pupil.  Contraction  of  the  iris  may  occur  under  the 
following  circumstances:  1,  On  exposure  of  the  eye  to  a  bright  light;  2,  On 
the  local  application  of  eserine  (active  principle  of  Calabar  bean);  3,  On  the 
administration  internally  cf  opium,  aconite,  and  in  the  early  stages  of  chloro- 
form and  alcohol  poisoning;  4,  On  division  of  the  cervical  sympathetic  or  of 
stimulation  of  the  third  nerve.  Dilatation  of  the  pupil  occurs,  1,  in  a  dim 
light;  2,  when  the  eye  is  focussed  for  distant  objects;  3,  on  the  local  applica- 
tion of  atropine  and  its  allied  alkaloids;  4,  on  the  internal  administration  of 
atropine  and  its  allies;  5,  in  the  later  stages  of  poisoning  by  chloroform, 
opium,  and  other  drugs;  6,  on  paralysis  of  the  third  nerve;  7,  on  stimulation 
of  the  cervical  sympathetic,  or  of  its  center  in  the  floor  of  the  front  of  the 
aqueduct  of  Sylvius.  The  contraction  of  the  pupil  is  under  the  control  of 
a  center  in  the  floor  of  the  aqueduct  beneath  the  anterior  corpora  quadri- 
gemina.  This  center  is  reflexly  stimulated  by  a  bright  light,  and  the  dilata- 
tion when  the  center  is  not  in  action  is  due  to  the  stimulation  of  the  radial 
fibers  of  the  iris  by  sympathetic  nerves.     In  addition,  it  appears  that  both 


648  THE    SENSES 

contraction  and  dilatation  may  be  produced  by  a  local  action  of  certain  drugs 
which  is  independent  of  and  probably  often  antagonistic  to  the  action  of  the 
central  apparatus  of  the  third  and  sympathetic  nerves. 

The  close  coordination  between  the  two  eyes  is  nowhere  better  shown 
than  by  the  condition  of  the  pupil.  If  one  eye  be  shaded  by  the  hand  its 
pupil  will  of  course  dilate;  the  pupil  of  the  other  eye  will  also  dilate,  though 
unshaded,  due  to  crossed  reflex  action. 

Defects  in  the  Optical  Apparatus.  Under  this  head  we  may  con- 
sider the  defects  known  as:  i,  Spherical  Aberration;  2,  Chromatic  Aberra- 
tion; 3,  Astigmatism;  4,  Myopia;  5,  Hypermetropia. 

The  normal  or  emmetropic  eye  is  so  perfect  that  parallel  rays  are  brought 
exactly  to  a  focus  on  the  retina  without  any  effort  of  accommodation,  figure 
466.  Hence  all  objects  except  near  ones  (in  practice  all  objects  at  a  distance 
of  twenty  feet  or  more)  are  seen  without  any  effort  of  accommodation;  in 
other  words,  the  far-point  of  the  normal  eye  at  rest  is  at  an  infinite  distance. 
In  viewing  near  objects  we  are  conscious  of  the  effort  (the  contraction  of 
the  ciliary  muscle)  by  which  the  anterior  surface  of  the  lens  is  rendered 
more  convex,  and  rays  which  would  otherwise  be  focussed  behind  the  retina 
are  converged  upon  the  retina. 

Spherical  Aberration.  The  rays  of  a  cone  of  light  from  an  object  situated 
in  the  field  of  vision  do  not  all  meet  in  the  same  point,  owing  to  the  greater 
refraction  of  the  rays  which  pass  through  the  circumference  of  a  lens  than 
that  of  those  traversing  its  central  portion.  This  defect  is  known  as  spherical 
aberration.  In  the  camera,  telescope,  microscope,  and  other  optical  instru- 
ments it  is  remedied  by  the  interposition  of  a  screen  with  a  circular  aperture 
in  the  path  of  the  rays  of  light,  cutting  off  all  the  marginal  rays  and  allow- 
ing the  passage  only  of  those  near  the  center.  Such  correction  is  effected 
in  the  eye  by  the  iris,  which  forms  a  diaphragm  to  cover  the  circumference  of 
the  lens,  and  prevents  the  rays  from  passing  through  any  part  of  the  lens 
but  its  center,  which  corresponds  to  the  pupil.  The  iris  is  pigmented  to  pre- 
vent the  passage  of  rays  of  light  through  its  substance.  The  image  of  an 
object  will  be  most  defined  and  distinct  when  the  pupil  is  small,  if  the  light 
is  abundant;  so  that,  while  a  sufficient  number  of  rays  are  admitted,  the 
narrowness  of  the  pupil  may  prevent  the  production  of  indistinctness  of  the 
image  by  spherical  aberration.  But  even  the  image  formed  by  the  rays  passing 
through  the  circumference  of  the  lens,  when  the  pupil  is  much  dilated,  as  in 
the  dark,  or  in  a  feeble  light,  may,  under  certain  circumstances,  be  well  defined. 

Distinctness  of  vision  is  further  secured  by  the  pigment  of  the  outer  sur- 
face of  the  retina  and  of  the  posterior  surface  of  the  iris  and  the  ciliary  proc- 
esses, which  absorbs  any  rays  of  light  that  may  be  reflected  within  the  eye, 
and  prevents  their  being  thrown  again  upon  the  retina  so  as  to  interfere 
with  the  images  formed  there.  The  pigment  of  the  retina  is  especially  im- 
portant in  this  respect;   for  with  the  exception  of  its  outer  layer  the  retina  is 


DEFECTS    IN    THE    OPTICAL    APPARATUS  649 

very  transparent;  and  if  the  surface  behind  it  were  not  of  a  dark  color,  but 
capable  of  reflecting  the  light,  the  luminous  rays  which  had  already  acted 
on  the  retina  would  be  reflected  again  and  would  fall  upon  other  parts  of 
the  same  membrane,  producing  indistinctness  of  the  images. 

Chromatic  Aberration.  In  the  passage  of  light  through  the  periphery  of 
an  ordinary  convex  lens,  decomposition  of  each  ray  into  its  elementary  colored 
parts  commonly  ensues,  and  a  colored  margin  appears  around  the  image, 
owing  to  the  unequal  refraction  which  the  elementary  colors  undergo.  This 
is  termed  chromatic  aberration.  It  is  corrected  by  the  use  of  lenses  constructed 
of  alternate  layers  of  glass  of  different  refractive  indices  so  ground  that  they 
produce  chromatic  dispersion  in  opposite  directions  and  thus  mutually  correct 
any  chromatic  aberration  which  may  have  resulted.  The  human  eye  has 
considerable  chromatic  aberration,  as  may  readily  be  demonstrated,  experi- 
ment 13,  page  673. 

An  ordinary  ray  of  white  light  in  passing  through  a  prism  has  its  con- 
stituent rays  refracted  in  unequal  degrees,  and  therefore  appears  as  colored 
bands  fading  off  into  each  other,  known  as  the  spectrum.  The  colors  of  the 
spectrum  are  arranged  as  follows:  red,  orange,  yellow,  green,  blue,  indigo, 
violet;  of  these  the  red  ray  is  the  least,  and  the  violet  the  most,  refracted. 
Hence,  as  Helmholtz  has  shown,  the  rays  from  a  white  point  cannot  be  ac- 
curately focussed  on  the  retina,  for  if  we  focus  for  the  red  rays,  the  violet  are 
out  of  focus,  and  vice  versa:  such  objects,  if  not  exactly  focussed,  are  often 
seen  surrounded  by  a  pale  yellowish  or  bluish  fringe. 

For  similar  reasons  a  red  surface  looks  nearer  than  a  blue  one  at  an  equal 
distance,  because,  the  red  rays  being  less  refrangible,  a  stronger  effort  of 
accommodation  is  necessary  to  focus  them,  and  the  eye  is  adjusted  as  if  for 
a  nearer  object,  and  therefore  the  red  surface  appears  nearer,  experiment  13. 

Astigmatism.  This  defect,  which  was  first  discovered  by  Airy,  is  due  to 
a  greater  curvature  of  the  refractive  surfaces  of  the  eye  in  certain  meridians 
than  in  others.  Thus  vertical  and  horizontal  lines  crossing  each  other  can- 
not both  be  focussed  on  one  plane;  one  set  stands  out  clearly,  and  the  others 
are  blurred  and  indistinct.  This  defect,  which  is  generally  present  in  a  slight 
degree  in  all  eyes,  is  usually  seated  in  the  cornea,  but  occasionally  in  the 
lens  as  well. 

The  plane  of  greatest  curvature  in  the  cornea  is  usually  in  the  vertical 
meridian,  a  fact  which  doubtless  comes  from  the  pressure  of  the  eyelids  during 
development.  If  one  looks  at  figure  463,  A  or  B,  with  one  eye,  the  three  lines 
in  the  radii  of  the  figure  will  be  seen  with  unequal  distinctness.  Certain 
sets  will  stand  out  sharp  and  black  and  others  dim  and  with  indistinct  out- 
lines, and  if  the  astigmatism  is  great  enough  the  three  lines  may  not  be  dis- 
tinguished. Figures  C  and  D  of  this  series  enable  one  to  detect  minute  traces 
of  astigmatism  with  great  accuracy. 

It  is  somewhat  difficult  to  picture  the  rays  from  a  luminous  point  in  their 


GoO 


THE     SENSES 


courses  through  eyes  which  have  this  defect,  but  an  examination  of  figure 
464  will  show  their  refraction.  In  this  figure  four  rays  coming  from  the 
point  L  in  the  arrows  are  represented  as  striking  on  the  refractive  surface 
of  the  eye  atyl,  B,  C,  D,  and  being  converged  toward  a  focus.  The  rays  A,  C, 
separated  by  vertical  line  on  the  refractive  surface,  are  focussedat  fu  while  the 
lines  A,  B,  separated  by  the  horizontal  distance  on  the  refractive  surface,  are 


b  c 

Fig.   463. — Astigmatic  Charts. 


brought  to  a  focus  at  /,.  The  point  L,  therefore,  has  two  apparent  focal  points, 
one  point  composed  of  the  rays  that  strike  in  a  horizontal  plane,  /,,  the  other 
of  rays  that  strike  in  a  vertical  plane,  fv  If  the  retina  of  the  eye  be  placed 
at  Jt  it  will  see  an  image  of  a  point  with  indistinct  horizontal  rays.  If  placed 
at  the  position  /,  it  will  see  a  luminous  point  with  indistinct  rays  in  the 
vertical  plane.  If  the  series  of  points  in  the  arrow  MN  be  considered, 
it  is  evident  that  at  the  position  /,  the  rays  which  fall  in  the  vertical  plane 
will  form  distinct  foci,  while  those  that  fall  in  the  horizontal  plane  will  form 
overlapping  diffuse  images  in  that  plane.  Since  they  are  overlapping,  they 
will  not  appear  separate  except  at  the  ends  of  the  image  of  the  arrow,  and  the 
arrow  will  therefore  be  seen  distinctly.  If  the  position  /2  is  considered 
where  the  rays  of  the  horizontal  plane  are  focussed,  then  it  is  evident  that 


<■        f,    c         f, 
Fig.  464. — The  Unequal  Refraction  of  Rays  in  an  Astigmatic  Eye.     (John  Green.) 


the  points  in  the  arrow  MN  will  present  a  series  of  rays  or  halos  in  the 
vertical  plane,  thus  rendering  its  outline  very  dim  or  indistinct.  The  condi- 
tion with  the  arrow  OP  is  exactly  the  reverse.  Hence,  in  the  astigmatic 
eye  the  images  of  the  horizontal  arrow  MN  will  be  distinct  at  the  focus  }u 
while  the  image  of  the  vertical  arrow  OP  will  be  distinct  in  the  focus  /2,  and 
the  eye  cannot  see  the  two  lines  distinctly  at  the  same  time.    This  condition  is 


DEFECTS     IN     THE     OPTICAL     APPARATUS 


651 


further  illustrated  in   figure  465  which  represents  the  position  /t    shown   in 
figure  464. 

Myopia.  This  is  that  refractive  condition  of  the  eye  in  which  parallel 
rays  are  brought  to  a  focus  in  front  of  the  retina,  4,  figure  466.  It  is  due 
either  to  an  abnormal  elongation  of  the  eyeball,  antero-posteriorly,  or  to  an 
increase  in  the  convexity  of  the  refracting  surfaces,  or  to  both  of  these  con- 
ditions. Parallel  rays  are  focussed  in  front  of  the  retina,  and,  crossing, 
form  circles  on  the  retina.  Thus,  the  images  of  distant  objects  are  blurred 
and  indistinct.  The  eye  is,  as  it  were,  permanently  adjusted  for  a  near  point. 
Rays  from  a  point  near  the  eye  are  exactly  focussed  on  the  retina.  But  those 
which  issue  from  any  object  beyond  a  slight  distance,  the  myopic  far-point, 
which  is  less  than  twenty  feet,  cannot  be  distinctly  focussed.  This  defect 
is  corrected  by  concave  glasses,  which  cause  parallel  rays  entering   the  eye 


Fig.  465. — Diagram  of  Character  of  Retinal  Images  in  Astigmatism.     (John  Green.) 


to  diverge.  Such  glasses  of  course  are  needed  only  to  give  a  clear  vision  of 
distant  objects.     For  near  objects  they  are  not  required. 

Hypermetropia.  This  is  that  refractive  condition  of  the  eye  in  which 
parallel  rays  are  brought  to  a  focus  behind  the  retina,  3,  figure  466.  It  is  the 
opposite  of  myopia,  and  is  due  either  to  an  abnormal  shortening  of  the  eye- 
ball, antero-posteriorly,  or  to  a  decrease  in  the  convexity  of  the  refracting 
surfaces,  or  both.  Parallel  rays  entering  the  eye  at  rest  are  focussed  behind 
the  retina.  An  effort  of  accommodation  is  therefore  required  to  focus  parallel 
rays  on  the  retina.  When  the  rays  are  sharply  divergent,  as  in  viewing  a  very 
near  object,  the  accommodation  is  insufficient  to  focus  them.  Thus,  both 
ne;:r  and  distant  objects  require  an  effort  of  accommodation,  and  the  eye 
is  under  a  constant  strain  which  produces  in  the  end  various  nervous,  as  well 
as  ocular,  disorders.  This  defect  is  obviated  by  the  use  of  convex  glasses, 
which  render  the  pencils  of  light  more  convergent.  Such  glasses  are  espe- 
cially needed  for  near  objects,  as  in  reading,  etc.  They  are  also  required  for 
distant  vision  to  rest  the  eye  by  relieving  the  ciliary  muscle  from  constant  work. 

Presbyopia.  Presbyopia  is  a  condition  of  diminished  range  of  accom- 
modation.    It  takes  place  with  considerable  uniformity  from  youth  to  old  age. 


THE    SENSES 

It  is  not  a  disease,  but  a  physiological  process  which  every  eye  undergoes  as 
its  owner  grows  older.  It  is  due  to  a  gradual  diminution  of  elasticity  of  the 
lens  by  a  sort  of  sclerosis  from  the  center  toward  the  periphery.  It  begins 
even  in  childhood,  but  advances  so  slowly  that  it  is  not  until  the  age  of 
twenty-five  or  so  that  a  distinct,  though  small,  nucleus  is  present.  With 
advancing  years  the  process  goes  on  until  finally  the  lens  becomes  inelastic 


Fig.  466. — Diagram  Showing:  1,  Normal  or  emmetropic  eye  bringing  parallel  rays  exactly  to  a 
focus  on  the  retina;  2,  normal  eye  at  rest,  showing  that  light  from  a  near  point  is  focussed  behind  the 
retina,  but  by  increasing  the  curvature  of  the  anterior  surface  of  the  lens  (shown  by  dotted  lines) 
the  rays  are  focussed  on  the  retina;  3,  hypermetropic  eye.  In  this  case  the  axis  of  the  eye  is  shorter, 
and  the  lens  normal  (or  the  lens  may  be  natter  than  normal  and  the  eyeball  normal) ;  parallel 
rays  are  focussed  behind  the  retina;  4,  myopic  eye.  In  this  case  the  lens  is  too  convex  (or  the 
axis  of  the  eye  is  abnormally  long) ;  parallel  rays  are  focussed  in  front  of  the  retina. 

and  is  unable  to  assume  a  shape  convex  enough  to  focus  rays  from  a  near 
object  upon  the  retina,  as  in  reading.  The  defect  is  remedied  by  the  use 
of  convex  lenses  equivalent  to  the  loss  in  accommodation. 

Visual  Sensations,  from  Excitation  of  the  Retina.  Light  is  the 
normal  agent  in  the  excitation  of  the  retina.  The  only  portion  of  the  retina 
capable  of  reacting  to  the  stimulus  is  the  rod  and  cone  layer.  The  proofs  of 
this  statement  may  be  summed  up  thus:   i.  The  point  of  entrance  of  the  optic 


VISUAL   SENSATIONS,    FROM   EXCITATION   OF   THE    RETINA  653 

nerve  into  the  retina,  where  the  rods  and  cones  are  absent,  is  insensitive  to 
light  and  is  called  the  blind  spot.  The  phenomenon  itself  is  very  readily 
demonstrated.  If  we  close  one  eye,  and  direct  the  other  upon  a  point  at 
such  a  distance  to  the  side  of  any  object  that  the  image  of  the  latter  must 
fall  upon  the  retina  at  the  point  of  entrance  of  the  optic  nerve,  its  image  is 
lost.  If,  for  example,  we  close  the  left  eye,  and  direct  the  axis  of  the  right 
eye  steadily  toward  the  circular  spot  in  figure  467,  while  the  page  is  held  at 
a  distance  of  about  six  inches  from  the  eye,  both  dot  and  cross  are  visible. 
On  gradually  increasing  the  distance  between  the  eye  and  the  object,  by 
removing  the  book  farther  and  farther  from  the  face,  keeping  the  right  eye 
steadily  on  the  dot,  it  will  be  found  that  suddenly  the  cross  disappears  from 
view,  while  on  removing  the  book  still  farther  it  suddenly  comes  into  view 
again.  The  cause  of  this  phenomenon  is  simply  that  the  portion  of  retina 
which  is  occupied  by  the  entrance  of  the  optic  nerve  is  quite  blind;  and  there- 
fore that  when  it  alone  occupies  the  field  of  vision  objects  cease  to  be  visible. 

•  + 

Fig.  467. — Diagram  for  Demonstrating  the  Blind  Spot- 

2.  In  the  fovea  centralis  and  macula  lutea,  which  contain  rods  and  cones  but 
no  optic-nerve  fibers,  light  produces  the  greatest  effect.  In  the  latter,  cones 
occur  in  large  numbers,  and  in  the  former  cones  without  rods  are  found, 
whereas  in  the  rest  of  the  retina,  which  is  not  so  sensitive  to  light,  there  are 
fewer  cones  than  rods.  We  may  conclude,  therefore,  that  cones  are  even 
more  important  to  vision  than  rods.  3.  If  a  small  lighted  candle  be  moved 
to  and  fro  at  the  side  of  and  close  to  one  eye  in  a  dark  room  while  the  eyes 
look  steadily  forward  into  the  darkness,  a  remarkable  branching  figure, 
Purkinje's  figures,  is  seen  floating  before  the  eye,  consisting  of  dark  lines  on 
a  reddish  ground.  As  the  candle  moves,  the  figure  moves  in  the  opposite 
direction,  and  from  its  whole  appearance  there  can  be  no  doubt  that  it  is  a 
reversed  picture  of  the  retinal  vessels  projected  before  the  eye.  The  two 
large  branching  arteries  passing  up  and  down  from  the  optic  disc  are  clearly 
visible,  together  with  their  minutest  branches.  A  little  to  one  side  of  the  disc, 
in  a  part  free  from  vessels,  is  seen  the  yellow  spot  in  the  form  of  a  slight  de- 
pression. This  remarkable  appearance  is  due  to  shadows  of  the  retinal 
vessels  cast  by  the  candle.  The  branches  of  these  vessels  are  chiefly  dis- 
tributed in  the  nerve  fibers  and  ganglionic  layers;  and  since  the  light  of  the 
candle  falls  on  the  retinal  vessels  from  in  front,  the  shadow  is  cast  behind 
them,  and  hence  those  elements  of  the  retina  which  perceive  the  shadows 
must  also  lie  behind  the  vessels.  Here,  then,  we  have  a  clear  proof  that  the 
light-perceiving  elements  of  the  retina  are  not  the  fibers  of  the  optic  nerve 
forming  the  innermost  layer  of  the  retina,  but  the  external  layers  of  the  retina, 
the  rods  and  cones. 


G54  THE     SENSES 

When  light  falls  on  the  rods  and  cones  it  produces  changes  which  develop 
nerve  impulses  that  are  transmitted  by  the  chain  of  neurones  extending 
through  the  retina,  the  optic  nerve  and  chiasma,  the  geniculate  bodies,  etc., 
to  the  cerebral  cortex  of  the  occipital  lobe,  which  is  the  sensorium  for  visual 
sensations.  We  have  already  seen  that  the  eye  possesses  a  wonderful  me- 
chanical perfection  for  receiving  and  focussing  light  on  definite  parts  of  the 
retina.  A  comparison  of  visual  sensations  shows  that  there  are  corresponding 
qualities  in  the  sensation,  as,  for  example,  its  intensity,  duration,  localiza- 
tion, complexity,  etc. 

Duration  of  Visual  Sensations.  The  duration  of  the  sensation  pro- 
duced by  a  luminous  impression  on  the  retina  is  always  greater  than  that 
of  the  stimulus  which  produces  it.  However  brief  the  luminous  impression, 
the  effect  on  the  retina  always  lasts  for  about  one-twentieth  of  a  second. 
Thus,  suppose  an  object  in  motion,  say  a  horse,  to  be  revealed  on  a  dark 
night  by  a  flash  of  lightning,  the  image  remaining  on  the  retina  during  the 
time  of  the  flash.  The  object  is  really  revealed  for  such  an  extremely  short 
period  (a  flash  of  lightning  being  almost  instantaneous)  that  no  appreciable 
movement  could  have  taken  place  in  the  period  during  which  the  stimulus 
was  produced  on  the  retina  of  the  observer.  The  horse  would  appear  stand- 
ing in  the  position  of  motion  for  about  a  twentieth  of  a  second,  though  he 
would  not  be  seen  to  make  any  motions.  And  the  same  fact  is  proved  in  a 
reverse  way.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen  as  dis- 
tinct objects,  because  at  every  point  of  the  field  of  vision  over  which  the  re- 
volving spokes  pass,  a  given  impression  has  not  faded  before  another  comes 
to  replace  it.     Thus  every  part  of  the  interior  of  the  wheel  appears  filled. 

The  duration  of  the  after-sensation  produced  by  an  object  is  greater  in  a 
ratio  proportionate  to  the  duration  of  the  impression  which  caused  it.  Hence, 
the  image  of  a  bright  object,  as  of  the  light  of  a  window,  may  be  perceived  in 
the  retina  for  a  brief  period,  the  positive  after-image.  If,  however,  the  primary 
stimulation  is  sharp  and  intense  there  will  follow  presently  an  appearance  of 
the  window  in  which  all  the  contrasted  lights  are  reversed,  the  negative  after- 
image. 

Intensity  of  Visual  Sensations.  It  is  quite  evident  that  the  more 
luminous  a  body  the  more  intense  is  the  stimulus  it  produces.  But  the  in- 
tensity of  the  sensation  is  not  directly  proportional  to  the  intensity  of  the 
luminosity  of  the  object.  It  is  necessary  for  light  to  have  a  certain  intensity 
before  it  can  excite  the  retina,  but  it  is  impossible  to  fix  an  arbitrary  limit 
to  the  power  of  excitability.  As  in  other  sensations,  so  also  in  visual  sensa- 
tions, a  stimulus  may  be  too  feeble  to  produce  a  sensation.  If  it  be  increased 
in  amount  sufficiently,  it  reaches  a  point  that  is  intense  enough  to  produce  an 
effect;  this  is  a  minimal  or  threshold  stimulus.  The  amount  of  increase  in 
the  stimulus  that  produces  a  perceptible  change  in  the  sensation  is  at 
first  very  slight,  but  later  quite  great.     It  does  not  depend  on  the  absolute 


INTENSITY    OF    VISUAL    SENSATIONS 


655 


change  of  intensity  of  the  stimulus,  but  is  proportional  to  the  intensity  of  the 
stimulus  already  acting,  Weber's  law. 

This  law,  which  is  true  only  within  certain  limits,  may  be  best  under- 
stood by  an  example.  "When  the  retina  has  been  stimulated  by  the  light  of 
one  candle,  the  light  of  two  candles  will  produce  a  difference  in  sensation 
which  can  be  easily  and  distinctly  felt.  If,  however,  the  first  stimulus  is  that 
of  an  electric  arc-light,  the  addition  of  the  light  of  a  candle  will  make  no  dif- 
ference in  the  sensation.  So,  generally,  for  an  additional  stimulus  to  be  felt, 
it  may  be  proportionately  small  if  the  original  stimulus  is  small,  and  must 
be  greater  if  the  original  stimulus  is  great.  The  stimulus  increases  as  the 
numbers  expressing  its  strength,  while  the  sensation  increases  as  the 
logarithms. 

Every  one  is  familiar  with  the  fact  that  it  is  quite  impossible  to  see 
the  fundus  or  back  of  another  person's  eye  by  simply  looking  into  it.  The 
interior  of  the  eye  forms  a  perfectly  black  background  to  the  pupil.  The  same 


Fig.  468.— Diagram  to  Illustrate  the  Action  of  the  Ophthalmoscope  when  a  Plane  Concave 
Glass  is  Used,  c.  Observer's  eye.  The  light  reflected  from  any  point,  d,  on  retina  of  o,  would 
naturally  be  focussed  at  c;  if  the  lens  b  is.  used  it  would  be  focussed  at  i,  in  other  words,  at  back 
of  c.  The  image  would  be  enlarged,  as  though  of  g,  and  would  be  inverted.  (After  McGregor  Rob- 
ertson.) 

remark  applies  to  an  ordinary  photographic  camera,  and  may  be  illustrated 
by  the  difficulty  we  experience  in  seeing  into  a  room  from  the  street  through 
the  window,  unless  the  room  be  lighted  from  within.  In  the  case  of  the 
eye  this  fact  is  partly  due  to  the  feebleness  of  the  light  reflected  from  the 
retina,  most  of  it  being  absorbed  by  the  retinal  pigment.  But  the  difficulty 
is  due  more  to  the  fact  that  every  such  ray  is  reflected  back  to  the  source  of 
light  and  cannot  be  seen  by  the  unaided  eye  without  intercepting  the  in- 
cident light  as  well  as  the  reflected  rays  from  the  retina.  This  difficulty  is 
surmounted  by  the  use  of  the  ophthalmoscope. 


The  ophthalmoscope,  brought  into  use  by  Hclmholtz,  consists  in  its  simplest  form 
of  a  concave  mirror  with  a  hole  in  it.  The  one  described  is  one  of  the  less  intricate  of  the 
modern  instruments.  It  consists  of,  a,  a  slightly  concave  mirror  of  metal  or  silvered  glass 
perforated  in  the  center,  and  fixed  into  a  handle;  and  b,  a  biconvex  lens  of  6  to  8  cm. 
focal  length.  Two  methods  of  examining  the  eye  with  this  instrument  are  in  common  use 
— the  direct  and  the  indirect :  both  methods  of  investigation  should  be  employed.  A  nor- 
mal eye  should  be  examined.  A  drop  of  a  solution  of  atropine  (two  grains  to  the  ounce) 
or  of  homatropine  hydrobromate  should  be  dropped  into  the  right  eye  only  about  twenty 
minutes  before  the  examination  is  commenced;    the  ciliary  muscle  is  thereby  paralyzed, 


656 


THE    SENSES 


the  power  of  accommodation  is  abolished,  and  the  pupil  is  dilated.  This  will  materially 
facilitate  the  examination;  but  it  is  quite  possible  to  observe  all  the  details  to  be  presently 
described  without  the  use  of  this  drug.  The  room  being  now  darkened,  the  observer  seats 
himself  in  front  of  the  person  whose  eye  he  is  about  to  examine,  placing  himself  upon  a 


Fig.  469. — Diagram  to  Illustrate  Action  of  Ophthalmoscope  when  a  Biconvex  Glass  is  Used. 
The  figure  d  on  retina  of  a  is  under  ordinary  conditions  focussed  at  /  and  inverted.  If  the  lens 
b  be  placed  between  eyes,  the  image  h  is  seen  by  the  eye  c  as  an  enlarged  image.  (After  Mc- 
Gregor Robertson.) 


somewhat  higher  level.  A  subdued  but  steady  light  is  placed  close  to  the  left  ear  of  the 
patient  in  the  examination  of  the  right  eye.  Guiding  the  mirror  in  his  right  hand,  and 
looking  through  the  central  hole,  the  operator  directs  a  beam  of  light  into  the  eye  of  the 
patient.  A  red  glare,  called  in  practice  the  reflex,  due  to  the  illumination  of  the  retina,  is 
seen.  The  patient  is  then  told  to  look  at  the  little  finger 
of  the  observer's  right  hand  as  he  holds  the  mirror;  to 
effect  this  the  eye  is  rotated  somewhat  inward,  and  at  the 
same  time  the  reflex  changes  from  red  to  a  lighter  color, 
owing  to  the  reflection  from  the  optic  disc.  The  observer 
now  approximates  the  mirror,  and  with  it  his  eye  to  the 
eye  of  the  patient,  taking  care  to  keep  the  light  fixed  upon 
the  pupil,  so  as  not  to  lose  the  reflex.  At  a  certain  dis- 
tance, which  varies  with  the  refractive  power  in  different 
eyes,  but  is  usually  an  interval  of  about  two  or  three 
inches  between  the  observed  and  the  observing  eye,  the 
vessels  of  the  retina  will  become  visible  as  lines  running  in 
different  directions.  The  smaller  and  brighter  red  arteries 
can  be  distinguished  from  the  larger  and  darker  colored 
veins.  An  examination  of  the  fundus  of  the  eye  reveals 
the  optic  disc  and  the  entrance  of  the  blood-vessels,  the 
macula  lutea,  and  the  fovea  centralis.  No  blood-vessels 
are  seen  in  the  fovea.  This  constitutes  the  direct  method 
of  examination,  figure  468;  by  it  the  various  details  of 
the  fundus  are  seen  as  they  really  exist,  and  it  is  this 
method  which  should  be  adopted  for  ordinary  use. 

If  the  observer  is  ametropic,  i.e.,  is  myopic  or  hyper- 
metropic, he  will  be  unable  to  employ  the  direct  method 
of  examination  until  he  has  remedied  his  defective  vision 
by  the  use  of  proper  glasses. 

In  the  indirect  method,  figure  469,  the  patient  is 
placed  as  before,  and  the  operator  holds  the  mirror  in 
his  right  hand  at  a  distance  of  30  to  40  cm.  from  the 
patient's  right  eye.  At  the  same  time  he  rests  his  left 
little  finger  lightly  upon  the  patient's  right  temple,  and 
holding  the  lens  between  his  thumb  and  forefinger,  two 
or  three  inches  in  front  of  the  patient's  eye,  directs  the 
light  through  the  lens  into  the  eye.  The  red  reflex,  and  subsequently  the  white  one, 
having  been  gained,  the  operator  slowly  moves  his  mirror,  and  with  it  his  eye,  toward  or 
away  from  the  face  of  the  patient,  until  the  outline  of  one  of  the  retinal  vessels  becomes 
visible,  when  very  slight  movements  on  the  part  of  the  operator  will  suffice  to  bring  into 


Fig.  470. — The  Ophthalmo- 
scope. The  small  upper  mir- 
ror is  for  direct,  the  larger  for 
indirect,  illumination. 


THE    FIELD    OF    VISION 


657 


view  the  details  of  the  fundus  above  described,  but  the  image  will  be  much  smaller  and  in- 
verted. The  lens  should  be  kept  at  a  fixed  distance  of  two  or  three  inches,  the  mirror 
being  alone  moved  until  the  disc  becomes  visible:  should  the  image  of  the  mirror  obscure 
the  disc,  the  lens  may  be  slightly  tilted. 

The  Field  of  Vision.  The  field  of  vision  of  an  eye  is  that  part 
of  the  external  world  which  can  be  seen  by  it  when  the  eye  is  fixed.  Under 
such  circumstances  objects  near  the  axis  of  vision  stimulate  points  in  the  retina 
near  the  fovea  or  on  it,  while  objects  at  an  angle  of  6o°  to  900  from  the  axis 


Fig.  471- 


-Perimeter  Chart,  Showing  Extent  of  Field  of  Vision  for  White  Light  and  to  the 
^Colors  Red,  Green,  Yellow,  and  Blue.      (Krapart.) 


of  vision  stimulate  regions  of  the  opposite  side  of  the  retinal  cup,  i.e.,  the 
retinal  field  is  inverted. 

The  perimeter  is  an  instrument  for  measuring  the  field  of  vision  in  terms 
of  angular  measure.  When  a  field  is  charted  by  means  of  the  perimeter  it 
is  revealed  that  objects  can  be  seen  further  out  in  the  field  in  some  directions 
than  in  others.  For  example,  objects  in  the  temporal  field  can  be  seen  at 
an  angle  of  900  to  ioo°,  while  on  the  nasal  side  they  are  seen  only  6o°  to  700. 
If  the  head  is  turned  to  the  right  or  the  left  while  keeping  the  eye  fixed,  it  is 
found  that  objects  are  seen  at  a  greater  angle.  This  shows  that  the  limita- 
tions are  due  to  the  facial  boundaries  of  the  eye  preventing  the  light  from 
entering  the  eye  and  not  from  lack  of  sensitiveness  of  the  retina.  In  fact 
the  retina  is  sensitive  to  light  out  to  the  ora  serrata. 

Localization  in  the  Retina.  Careful  exploration  of  the  retina  with 
the  perimeter  gives  a  measure  not  only  of  the  extent  of  the  visual  field  but  of 
42 


658  THE    SENSES 

its  acuteness  and  localization  in  different  areas  toward  the  periphery.  Con- 
sidering the  minimal  distance  apart  which  two  luminous  points  must  be  to 
be  distinguished  as  two,  it  is  found  that  when  the  image  falls  on  the  fovea 
the  two  points  may  be  very  near  together,  as  little  as  one  minute  or  even  less. 
Two  stars  can  be  seen  only  at  a  somewhat  greater  angular  distance,  two  to 
three  minutes.  One  minute  angular  measure  covers  an  area  on  the  retina  of 
a  trifle  over  4/;..  The  diameter  of  the  cones  is  about  2  n,  so  that  the  stimuli  in 
the  fovea  fall  on  at  least  two  separate  cones.  The  inference  seems  reasonable 
that  the  retina  in  its  most  sensitive  part  can  localize  stimuli  that  fall  on  ad- 
jacent cones. 

The  area  of  the  fovea  centralis  is  small,  from  0.5  to  1.5  mm.  Outside  of 
its  area  the  acuteness  of  vision  quickly  falls  off.  The  fact  is  roughly  estimated 
by  fixing  the  vision  on  a  letter  in  the  printed  line  in  the  book  before  the 
reader  and  then  determining  the  number  of  letters  to  either  side  that  can  be 
identified.  The  height  of  these  letters  is  1.5  mm. ;  by  measuring  the  distance 
of  the  page  from  the  eye  one  can  quickly  calculate  the  area  of  distinct  vision 
on  the  retina.     Test  types  are  printed  on  the  basis  of  an  angle  of  five  minutes. 

In  the  outer  limits  of  the  retina  the  power  of  localizing  stimuli  is  very 
slight;  in  fact,  in  the  extreme  borders  of  the  field  it  is  difficult  to  determine 
other  than  general  form. 

Visual  Purple.  The  method  by  which  a  ray  of  light  is  able  to 
stimulate  the  endings  of  the  optic  nerve  in  the  retina  is  not  yet  understood. 
It  is  supposed  that  the  change  effected  by  the  agency  of  the  light  which  falls 
upon  the  retina  is  in  fact  a  chemical  alteration  in  the  protoplasm,  and  that 
this  change  initiates  a  nerve  impulse  that  is  transferred  to  the  optic  nerve 
endings.  The  discovery  of  a  certain  temporary  reddish-purple  pigmenta- 
tion of  the  outer  limbs  of  the  retinal  rods  in  certain  animals,  e.g.,  frogs,  which 
had  been  killed  in  the  dark,  forming  the  so-called  rhodopsin  or  visual  purple, 
appeared  likely  to  offer  some  explanation  of  the  matter,  especially  as  it  was 
also  found  that  the  pigmentation  disappeared  when  the  retina  was  exposed 
to  light,  and  reappeared  when  the  light  was  removed,  and  that  it  underwent 
distinct  changes  of  color  when  other  than  white  light  was  used.  It  Avas  also 
found  that  if  the  operation  were  performed  quickly  enough  and  in  the  dark, 
the  image  of  an  object,  optogram,  might  be  fixed  in  the  pigment  on  the  retina 
by  soaking  the  retina  of  an  animal  in  alum  solution. 

The  visual  purple  cannot,  however,  be  absolutely  essential  to  the  due  pro- 
duction of  visual  sensations,  as  it  is  absent  from  the  retinal  cones,  and  from 
the  macula  lutea  and  fovea  centralis  of  the  human  retina,  and  does  not  appear 
to  exist  at  all  in  the  retinae  of  some  animals,  e.g.,  bat,  dove,  and  hen,  which 
are,  nevertheless,  possessed  of  good  vision. 

However,  the  fact  remains  that  light  falling  upon  the  retina  bleaches  the 
visual  purple,  and  this  must  be  considered  as  one  of  its  effects.  It  has  been 
found  that  certain  pigments,  also  sensitive  to  light,  are  contained  in  the  inner 


VISUAL    PURPLE 


659 


segments  of  the  cones.  These  colored  bodies  are  said  to  be  oil  globules  of 
various  colors — red,  green,  and  yellow — called  chromophanes,  and  are  found 
only  in  the  retinae  of  animals  other  than  mammals.  The  rhodopsin  at  any 
rate  appears  to  be  derived  in  some  way  from  the  retinal  pigment,  since  the 
color  is  not  renewed  after  bleaching  if  the  retina  be  detached  from  its  pig- 
ment layer.  The  second  change  produced  by  the  action  of  light  upon  the 
retina  is  the  movement  of  the  pigment  cells.  On  the  stimulation  by  light 
the  granules  of  pigment  in  the  cells  which  overlie  the  outer  part  of  the  rod 
and  cone  layer  of  the  retina  become  diffused  into  the  parts  of  the  cells  be- 
tween the  rods  and  cones,  the  melanin  granules,  as  they  are  called,  passing 


Fig.  472. — Sections  of  Frog's  Retina  Showing  the  Action  of  Light  upon  the  Pigment  Cells  and 
upon  the  Rods  and  Cones  (von  Gendesen-Stort.)  A,  From  a  frog  which  had  been  kept  in  the 
dark  for  some  hours  before  death;  B,  from  a  frog  which  had  been  exposed  to  light  just  before  being 
killed.  Three  pigment  cells  are  shown  in  each  section.  In  A  the  pigment  is  collected  toward  the 
nucleated  part  of  the  cell,  in  B  it  extends  nearly  to  the  basis  of  the  rods.  In  A  the  rods,  outer 
segments,  were  colored  red  (the  detached  one  green) ;  in  B  they  had  become  bleached.  In  A  the 
cones,  which  in  the  frog  are  much  smaller  than  the  rods,  are  mostly  elongated;  in  B  they  are  all  con- 
tracted. 


down  into  tne  processes  of  the  pigment  cells.  A  movement  0}  the  cones  and 
possibly  of  the  rods  is  also  said  to  occur,  as  has  been  already  incidentally 
mentioned.  Under  the  influence  of  the  stimulus  of  light  the  outer  parts  of 
the  cones,  which  in  an  eye  protected  from  light  extend  to  the  pigment  layer, 
are  retracted.  It  is  even  thought  by  some  that  the  contraction  is  under 
the  control  of  the  nervous  system.  Finally,  according  to  the  careful  researches 
of  Dewar  and  McKendrick,  and  of  Holmgren,  it  appears  that  the  stimulus  of 
light  is  able  to  produce  an  action  current  in  the  retina.  McKendrick  believes 
that  this  is  the  electrical  expression  of  those  chemical  changes  in  the  retina 
of  which  we  have  already  spoken. 

Color  Sensations.      When  a  ray  of  sunlight  enters  the  eye  it  pro- 


660  THE    SENSES 

duces  a  sensation  of  white  light.  But  if  the  ray  first  passes  through  a  prism, 
then  it  produces  sensations  corresponding  to  the  colors  of  the  spectrum.  As 
is  well  known,  white  light  is  produced  by  vibrations  of  the  luminiferous  ether 
through  a  wide  range  of  vibration  rates.  When  a  beam  of  white  light  is 
passed  through  a  dispersing  prism  those  vibration  rates  of  low  frequency 
are  refracted  less  than  those  of  higher  frequency,  giving  rise  to  the 
spectrum.  Vibrations  of  the  luminiferous  ether  of  rates  just  outside  of  the 
spectral  rates  exist,  those  which  have  a  lower  rate  giving  rise  to  heat  rays, 
and  those  of  higher  rate  to  the  so-called  actinic  or  chemical  rays,  because 
they  exert  a  powerful  chemical  action.  Those  spectral  colors  which  stimu- 
late the  retina  to  produce  sensations  of  color  presumably  affect  the  retinal 
elements  through  chemical  changes  which  they  produce  there.  But  this 
matter  will  be  discussed  under  theories  of  color  vision. 

The  examination  of  color  sensations  reveals  certain  correspondences  be- 
tween the  physical  color  of  the  stimulus  and  the  resulting  color  perception. 
If  a  pure  spectral  color  be  allowed  to  fall  on  the  retina,  a  corresponding  simple 
sensation  is  produced.  If  two  colors  fall  on  the  same  portion  of  the  retina 
at  the  same  time,  a  sensation  is  produced  that  is  different  from  that  which 
occurs  when  either  color  alone  stimulates.  The  same  fact  holds  true  for 
three  colors  or  more.  In  fact,  three  spectral  colors  can  be  selected  which 
by  proper  combination  can  be  used  to  produce  sensations  of  all  the  colors  of 
the  spectrum.  Such  colors  are  called  the  fundamental  colors,  and  while 
the  choice  is  more  or  less  arbitrary,  red,  green,  and  violet  are  the  colors  usu- 
ally considered. 

Extent  of  the  Visual  Field  for  Color.  The  retina  is  most  sensitive 
to  color  in  the  region  of  the  macula  lutea.  If  by  means  of  the  perimeter  one 
explores  the  retina  to  spectral  red,  for  example,  it  is  found  that  the  color  can 
be  identified  only  at  a  distance  of  from  300  to  500  from  the  macula;  the 
limits  extending  out  somewhat  farther  on  the  nasal  side  of  the  retina,  that 
is,  the  part  corresponding  to  the  temporal  visual  field.  In  the  same  way  yel- 
low can  be  identified  for  from  400  to  700,  blue  from  400  to  500.  The  visual 
field  for  green  is  quite  restricted,  usually  extending  only  from  200  to  300. 
The  extent  of  the  color  visual  field  varies  greatly  in  different  individuals. 

Complemental  Colors,  and  After-images  of  Color.  Certain  colors, 
when  allowed  to  stimulate  the  retina  at  the  same  time,  tend  to  neutralize  each 
other.  That  is,  they  produce  sensations  approaching  white,  usually  some 
shade  of  gray,  which  will  have  a  tinge  of  one  or  the  other  primary  colors 
according  to  the  proportion  of  stimulation.  These  pairs  of  colors  are  called 
complemental  colors.  Each  spectral  color  has  its  complemental  color,  a  fact 
that  is  represented  in  figure  473.  The  complemental  colors  of  greatest  physi- 
cal significance  are  red  and  green  (greenish  blue),  yellow  and  deep  blue 
(indigo  blue),  green  (greenish  yellow),  and  violet. 

Positive  after-images  of  color  exist  for  a  brief  moment,  but  the  greatest 


COLOR-BLINDNESS  661 

significance  attaches  to  the  negative  after-images.  The  negative  after-images 
of  color  following  the  stimulus  of  colored  light  upon  the  retina  are  not  the 
sensation  of  color  produced  by  the  color  of  an  object,  but  are  the  opposite 
or  complemental  color.  The  after-image  of  red  is,  therefore,  green,  and 
that  of  green,  red;  that  of  violet,  yellow  and  of  yellow,  violet,  etc.  The 
same  relation  holds  with  the  other  colors.  A  condition  for  the  development 
of  a  strong  after-image  is  that  the  primary  image  shall  have  continued  to  a 
certain  degree  of  fatigue.     The  colors  which  reciprocally  excite  each  other 


C  GnenisKliluc  ) 

Yellow 


Violet 


JhdigCj 

OrOHOt 


JiiJ 


Fig.   473. — Geometrical  Color  Table  for  Determining  the  Complemental  Colors. 

in  the  retina  are  those  placed  at  opposite  points  in  the  color  table,  figure  473. 
The  after-images  of  color  are  most  intense  in  the  axis  of  the  visual  field  and 
are  not  always  present  in  the  periphery  of  the  retina,  as  can  readily  be  seen 
by  examining  the  chart,  figure  471. 

Color  sensations  may  also  be  produced  by  contrast.  Thus,  a  very  small 
dull  gray  strip  of  paper,  lying  upon  an  extensive  surface  of  any  bright  color, 
does  not  appear  gray,  but  has  a  faint  tint  of  the  color  which  is  the  comple- 
ment of  that  of  the  surrounding  surface.  A  strip  of  gray  paper  upon  a  green 
field,  for  example,  appears  to  have  a  tint  of  red,  and  when  lying  upon  a  red 
surface,  a  greenish  tint;  it  has  an  orange-colored  tint  upon  a  bright  blue 
surface,  and  a  bluish  tint  upon  an  orange-colored  surface;  a  yellowish  color 
upon  a  bright  violet,  and  a  violet  tint  upon  a  bright  yellow  surface.  The 
color  excited  thus  must  arise  as  an  opposite  or  antagonistic  condition  of  the 
retina,  and  the  opposite  conditions  of  which  it  thus  becomes  the  subject, 
would  seem  to  balance  each  other  by  their  reciprocal  reaction.  A  necessary 
condition  for  the  production  of  the  contrast  colors  is  that  the  part  of  the 
retina  in  which  the  new  color  is  to  be  excited  shall  be  in  a  state  of  compara- 
tive repose;  hence  the  small  object  itself  must  be  gray.  A  second  condition 
is  that  the  color  of  the  surrounding  surface  shall  be  very  bright. 

Color-Blindness.  Many  persons  are  unable  to  distinguish  one  or 
more  of  the  fundamental  colors,  and  therefore  have  different  perceptions 


662  THE    SENSES 

of  the  color  combination  from  that  of  the  normal  individual.  It  is  said  that 
from  4  to  5  per  cent  of  men  and  about  [  per  cent  of  women  are  defective  in 
color  vision.     This  defect  is  called  color-blindness. 

In  very  rare  cases  complete  color-blindness  exists.  Such  individuals 
distinguish  lights  and  shades  only,  that  is,  form.  A  more  common  defect, 
however,  is  the  absence  of  one  or  more  of  the  fundamental  color  sensations, 
the  most  common  of  all  being  the  red-blind,  or  the  red-green  blind.  The  red- 
green  blind  individual  cannot  distinguish  red  and  green  colored  yarns  from 
each  other  or  from  shades  of  gray  which  reflect  light  with  the  same  intensity. 
When  they  are  given  the  color  test  by  the  Holmgren  yarns,  they  indiscrim- 
inately mix  the  reds,  greens,  and  grays.  Cases  have  been  described  in  which 
the  individual  was  red-blind  alone,  or  green-blind  alone.  A  less  common  color 
defect  is  the  inability  to  distinguish  yellows  and  blues,  yellow-blue  blindness. 

Color-blindness  may  occasionally  arise  from  disease  or  accident,  but  it 
is  usually  congenital.  The  individual  often  does  not  discover'  his  defect  until 
examined  especially  for  his  color  vision.  He  may  have  learned  to  apply 
the  terms  green  and  red  to  surrounding  objects,  such  as  the  grass,  bricks,  etc., 
but  he  distinguishes  these  objects  by  slight  differences  in  intensity  of  lumi- 
nation,  form,  etc.,  and  not  by  the  sensations  of  color  which  the  normal 
individual  experiences. 

Theories  of  Color  Vision.  We  have  no  way  of  determining  the 
method  by  which  the  colors  stimulate  the  retina  other  than  our  inferences 
from  indirect  evidence.  It  is  probable  that  the  energy  of  light  vibration 
is  transformed  in  the  retinal  structures  into  either  physical  or  chemical  change, 
perhaps  the  latter.  Those  interested  in  the  phenomena  of  color  vision  gener- 
ally accept  one  of  two  theories,  or  their  modifications,  in  explanation  of 
the  facts. 

The  Yonng-Helmholtz  Theory  oj  Color  Vision.  This  theory  assumes 
that  there  are  three  fundamental  sensory  elements  in  the  retina  which  cor- 
respond to  and  are  stimulated  primarily  by  the  three  primary  colors — red, 
green,  and  violet.  The  theory  in  its  present  form  further  assumes  that  each 
color-perceiving  element  is  slightly  stimulated  by  others  of  the  spectral  rays, 
as  shown  in  figure  474.  When  red  rays  fall  upon  the  retina,  they  stimulate 
the  red-perceiving  elements  strongly  and  the  green  and  violet  very  feebly. 
The  resulting  sensation  is  that  of  red.  So  also  is  it  with  green  and  violet  rays. 
When  the  retina  is  stimulated  by  both  red  and  green  rays,  the  two  correspond- 
ing color-perceiving  elements  are  strongly  stimulated.  The  resulting  color 
perception,  however,  is  a  combination  of  the  two  sensations  and  corresponds 
to  some  region  of  the  spectrum  between  the  red  and  green,  according  to  the 
relative  intensity  of  the  two  stimuli.  When  all  three  color-perceiving  ele- 
ments are  stimulated  at  the  same  time,  this  theory  assumes  that  white  light 
will  be  perceived.  In  a  similar  manner  all  the  various  color  sensations  are 
arrived  at. 


theorip:s   of   color   vision 


663 


Hering's  Theory  of  Color  Vision.  This  theory  is  based  on  the  assump- 
tion that  there  are  chemical  substances  in  the  retina,  photogenic  substances, 
which  are  stimulated  by  the  colors  of  the  spectrum.  It  assumes  three  photo- 
genic substances  which  are  called  the  red-green,  the  yellow-blue,  and  the 


Fig.  474. — Diagram  to  Illustrate  the  Stimulating  Effects  of  the  Three  Primary  Colors.  (Young- 
Helmholtz  theory.)  1  is  the  red;  2,  green,  and  3,  violet,  primary  color  sensations.  The  lettering 
indicates  the  colors  of  the  spectrum.  The  diagram  indicates  by  the  height  of  the  curve  to  what 
extent  the  several  primary  sensations  ef  color  are  excited  by  vibrations  of  different  wave  lengths. 
(Helmholtz.) 

white-black  substances.  By  the  theory,  when  the  red-green  substance  is 
stimulated  by  red  or  green  light,  respectively,  the  former  produces  destruc- 
tive or  catabolic  changes,  the  latter  constructive  or  anabolic  changes,  in  the 
substance.  When  red  light  falls  upon  the  retina,  it  produces  catabolism  in 
the  red-green  substance,  which  in  turn  develops  a  nerve  impulse  that  arouses 


Fig.  475. — Diagram  to  Illustrate  the  Reactions  of  the  Three  Photogenic  Substances,  according 
to  Hering's  Theory.      (Foster.) 

the  sensation  of  red.  When  green  light,  on  the  other  hand,  stimulates  the 
retina,  it  produces  anabolism  of  the  red-green  substance  and  the  sensation  of 
green.  The  same  rule  holds  with  the  other  two  substances.  It  will  be 
noticed  that  this  theory  is  based  on  the  complemental  colors. 


(j(J4,  THE    SENSES 

When  we  apply  the  theories  mentioned  above  to  the  phenomena  of  color- 
contrast  and  color-blindness,  we  find  that  each  is  defective  in  some  point. 
By  the  Young-Helmholtz  theory  it  is  difficult  to  understand  the  perception 
of  the  sensation  black,  for  by  the  theory  black  could  be  perceived  only  as 
the  absence  of  all  colors,  and  it  is  generally  granted  that  there  is  a  distinct 
black  sensation  other  than  and  different  from  mere  darkness.  This  theory 
explains  those  cases  of  blindness  to  one  color,  as  red-blindness,  for  example. 
The  Hering  theory,  on  the  other  hand,  gives  us  a  rational  explanation  for 
positive  black  sensation,  and  is  particularly  applicable  to  the  observed  facts 
of  color-contrast  and  negative  color  after-images. 

Color  after-images,  as  for  instance  the  after-images  of  green  following 
stimulation  by  red  light,  are  readily  explained  by  Hering's  theory,  since  the 
strong  catabolism  in  the  red-green  substance  will  be  followed  immediately 
by  anabolism  to  bring  this  substance  up  to  its  normal  in  the  eye,  thus  pro- 
ducing the  after-image.  This  phenomenon  can  be  explained  by  the  Young- 
Helmholtz  theory  only  by  assuming  that  following  the  stimulation  by  red 
light  and  the  consequent  fatigue  of  red-perceiving  elements  there  is  sufficient 
light  entering  the  eye  to  stimulate  the  relatively  sensitive  green  and  violet 
perceiving  elements,  thus  producing  an  after-image.  Strong  after-images 
are  perceived  in  the  dark  room,  so  that  the  Hering  theory  is  most  applicable 
in  the  explanation  of  these  cases. 

Binocular  Vision.  When  one  looks  at  an  object  with  a  single  eye, 
the  eye  is  so  adjusted  that  the  axis  of  vision  is  directed  toward  the  object 
investigated.  This  is  called  ocular  fixation.  The  ocular  fixation  is  accom- 
plished by  the  coordinated  contractions  of  the  six  pairs  of  ocular  muscles. 
Its  purpose  is  to  bring  the  image  of  the  object  examined  in  the  external  visual 
field  as  nearly  as  possible  upon  the  macula  lutea.  In  binocular  vision  both 
eyes  are  fixed  on  the  same  point  in  the  visual  field.  A  projection  of  the 
visual  axis  of  each  eye  will  pierce  the  point  of  fixation  in  the  external  object. 
It  is  evident  that  objects  to  either  side  of  the  point  of  fixation  will  give  off 
rays  which  will  enter  the  eyes,  stimulating  fields  in  the  retina  on  the  opposite 
side  of  the  visual  axis.  An  examination  of  figure  476  will  show  that  each 
point  in  the  visual  field,  A,  B,  C,  D,  stimulates  corresponding  points,  a,  b,  c,  d, 
a',  bf,  cf,  d',  in  the  retinas  of  the  two  eyes,  a,  b,  c,  d,  and  a',  b',  c',  d',  are  corre- 
sponding points  in  the  two  retinas.  When  a  and  a'  are  stimulated  at  one 
and  the  same  time,  the  resulting  sensation  is  attributed  to  one  object  in  the 
visual  field,  A,  and  these  are  corresponding  points.  This  can  be  shown 
by  pressing  one  eye  out  of  its  normal  fixation  so  that  the  axes  of  the  two  eyes 
are  not  directed  toward  the  same  point.  If  one  eye  is  pressed  lightly  by  the 
thumb  while  examining  a  given  object,  as  soon  as  the  pressure  is  applied 
two  objects  will  appear.  This  phenomenon  is  known  as  diplopia.  Diplopia 
is  due  to  the  fact  that  the  images  of  visual  objects  do  not  fall  on  correspond- 
ing points  in  the  two  retina?. 


BINOCULAR    VISION  665 

The  parts  of  the  retina?  in  the  two  eyes  which  thus  correspond  to  each 
other  in  the  property  of  referring  the  images  which  affect  them  simulta- 
neously to  the  same  spot  in  the  field  of  vision,  are,  in  man,  just  those  parts 
which  would  correspond  to  each  other  if  one  retina  were  placed  exactly  in 
front  of  and  over  the  other,  as  in  figure  477.  Thus,  as  we  have  noticed  in 
speaking  of  the  distribution  of  the  optic  nerve  fibers,  the  temporal  portion 
of  one  eye  corresponds  to  or  is  identical  with  the  nasal  portion  of  the  other 
eye.     The  upper  part  of  one  retina  is  also  identical  with  the  upper  part  of 


Fig.  476. — Diagram  Showing  the  Symmetrical  Correspondence  of  the  Retinal  Fields.  N, 
Nodal  point;  F,  fovea  centralis.  The  observer  is  supposed  to  be  looking  down  upon  the  optical 
apparatus  from  above.  Note  that  the  line  CD,  which  is  on  the  lower  side  of  the  object,  is  the 
upper  side  of  the  image;  and  that  the  line  BD,  which  is  the  right  side  of  the  object,  is  the  left  side 
of  the  image,  which  brings  it  at  the  inner  segment  of  the  right  retina  and  the  outer  segment  of  the 
left  retina. 

the  other;  and  the  lower  parts  of  the  two  eyes  are  identical  with  each  other. 
The  distribution  of  the  optic  nerve  fibers  corresponds  with  the  distribution 
of  the  identical  points.  The  identical  points  on  the  upper  and  lower  parts 
of  the  retina?  may  also  be  shown  by  the  following  simple  experiment. 

Pressure  upon  any  part  of  the  ball  of  the  eye,  so  as  to  affect  the  retina, 
produces  a  luminous  circle,  seen  at  the  opposite  side  of  the  field  of  vision  to 
that  on  which  the  pressure  is  made.  If,  now,  in  a  dark  room,  we  press  with 
the  finger  at  the  upper  part  of  one  eye,  and  at  the  lower  part  of  the  other, 
two  luminous  circles  are  seen,  one  above  the  other;   so,  also,  two  figures  are 


<>()(! 


THE    SENSES 


seen  when  pressure  is  made  simultaneously  on  the  outer  or  the  inner  sides 
of  both  eyes.  But  if  pressure  be  made  with  the  fingers  upon  both  eyes 
simultaneously  at  their  lower  part,  one  luminous  ring  is  seen  at  the  middle 
of  the  upper  part  of  the  field  of  vision.  If  the  pressure  be  applied  to  the  upper 
part  of  both  eyes,  a  single  luminous  circle  is  seen  in  the  middle  of  the  field  of 
vision  below.  So,  also,  if  we  press  upon  the  outer  side  of  one  eye  and  upon 
the  inner  side  of  the  other  eye,  a  single  luminous  spot  is  produced,  and  is  appar- 


FlG. 


Fig.  478. 


Fig.   477. — Diagram  to  Show  the  Corresponding  Parts  of  the  Retina. 

Fig.   478. — Diagram  to  Show  the  Simultaneous  Action  of  the  Eyes  in  Viewing  Objects  in  Dif- 
ferent Directions. 


ent  at  the  extreme  right  of  the  field  of  vision.  The  hemispheres  of  the  two 
retinae  may,  therefore,  be  regarded  as  lying  one  over  the  other,  as  in  C,  figure 
477;  so  that  the  left  portion  of  one  eye  lies  over  the  identical  left  portion  of 
the  other  eye,  the  right  portion  of  one  eye  over  the  identical  right  portion  of 
the  other  eye;  and  with  the  upper  and  lower  portions  of  the  two  eyes,  a  lies 
over  a',  b  over  b',  and  c  over  cf.  The  points  of  the  one  retina  intermediate 
between  a  and  c  are  again  identical  with  the  corresponding  points  of  the  other 
retina  between  a'  and  c';  those  between  b  and  c  of  the  one  retina,  with  those 
between  V  and  c'  of  the  other.  If  the  axes  of  the  eyes,  A  and  B,  figure  478, 
be  so  directed  that  they  meet  at  a,  an  object  at  a  will  be  seen  singly,  for  the 
point  a  of  the  one  retina  and  a'  of  the  other  are  identical.  So,  also,  if  the 
object  ft  be  so  situated  that  its  image  falls  in  both  eyes  at  the  same  distance 
from  the  central  point  of  the  retina — namely,  at  b  in  the  one  eye  and  at  b'  in 
the  other — ft  will  be  seen  single,  for  it  affects  identical  parts  of  the  two  retina?. 
The  same  will  apply  to  the  object  y. 

The  reason  why  the  impressions  on  the  identical  points  of  the  two  retina; 
give  rise  to  but  one  sensation,  and  the  perception  of  but  a  single  image, 
must  either  lie  in  the  structural  organization  of  the  deeper  or  cerebral  por- 
tions of  the  visual  apparatus,  or  it  must  be  the  result  of  a  mental  operation; 


VISUAL     JUDGMENTS  667 

for  in  no  other  case  is  it  the  property  of  corresponding  nerves  of  the  two 
sides  ■  >f  the  body  to  refer  their  sensations  to  one  spot. 

Many  attempts  have  been  made  to  explain  this  remarkable  relation  be- 
tween the  eyes,  by  referring  it  to  anatomical  relation  between  the  optic  nerves. 
The  circumstance  of  the  inner  portion  of  the  fibers  of  the  two  optic  nerves 
decussating  at  the  commissure,  and  passing  to  the  eye  of  the  opposite  side, 
while  the  outer  portion  of  the  fibers  continue  their  course  to  the  eye  of  the 
same  side,  so  that  the  left  side  of  both  retinae  is  formed  from  one  root  of  the 
nerves,  and  the  right  side  from  the  other  root,  naturally  led  to  an  attempt 
to  explain  the  phenomenon  by  this  distribution  of  the  fibers  of  the  nerves. 
And  this  explanation  is  favored  by  cases  in  which  the  entire  half  of  one 
side  of  the  retina  sometimes  becomes  insensible. 

Visual  Judgments.  Form  and  Solidity.  The  estimation  of  the 
form  of  bodies  by  sight  is  the  result  partly  of  the  visual  sensation  and  partly 
of  the  association  of  ideas.  The  form  of  the  image  perceived  by  the  retina 
depends  wholly  on  the  outline  of  the  part  of  the  retina  affected;  the  sensa- 
tion alone  is  adequate  only  to  the  distinction  of  superficial  forms  from  each 
other  which  lie  in  one  plane,  as  of  a  square  from  a  circle.  But  the  idea  of  a 
solid  body,  as  a  sphere,  or  a  body  of  three  or  more  surfaces,  e.g.,  a  cube, 
can  be  attained  only  by  the  action  of  the  mind  in  constructing  it  from  the  dif- 
ferent superficial  images  seen  in  different  positions  of  the  eye  with  regard 
to  the  object,  and  (as  shown,  by  Wheatstone  and  illustrated  in  the  stereoscope), 
from  two  different  perspective  projections  of  the  body  being  presented  simul- 
taneously to  the  mind  by  the  two  eyes.  Hence,  when,  in  adult  age,  sight  is 
suddenly  restored  to  persons  blind  from  infancy,  all  objects  in  the  field  of 
vision  appear  at  first  as  if  painted  flat  on  one  surface;  and  no  idea  of  solidity 
is  formed  until  after  long  exercise  of  the  sense  of  vision  combined  with  that 
of  touch.  The  clearness  with  which  an  object  is  perceived,  irrespective  of 
accommodation,  would  appear  to  depend  largely  on  the  definiteness  of  stimu- 
lation of  the  rods  and  cones  which  its  retinal  image  covers.  Hence,  the  nearer 
an  object  is  to  the  eye,  within  the  limits  of  vision,  the  more  clearly  are  all 
its  details  seen.  Moreover,  if  we  want  carefully  to  examine  any  object,  we 
always  direct  the  eyes  straight  toward  it,  so  that  its  image  shall  fall  on  the 
yellow  spot,  which  has  already  been  shown  to  be  the  area  of  most  acute  vision. 

In  binocular  vision  the  images  of  an  object,  while  they  fall  in  approxi- 
mately corresponding  points  on  the  two  retinas,  are  never  absolutely  the  same. 

'When  an  object  is  placed  so  near  the  eyes  that  to  view  it  the  optic  axes 
must  converge,  a  different  perspective  projection  of  it  is  seen  by  each  eye, 
these  perspectives  being  more  dissimilar  as  the  convergence  of  the  optic  axes 
becomes  greater.  Thus,  if  any  figure  of  three  dimensions,  an  outline  cube, 
for  example,  be  held  at  a  moderate  distance  before  the  eyes,  and  viewed  with 
each  eye  successively  while  the  head  is  kept  perfectly  steady,  A,  figure  479, 
will  be  the  picture  presented  to  the  right  eye,  and  B  that  seen  by  the  left  eye. 


668 


THE     SENSES 


Wheatstone  has  shown  that  on  this  circumstance  depends  in  a  great  measure 
our  conviction  of  the  solidity  of  an  object,  or  of  its  projection  in  relief.  If 
different  perspective  drawings  of  a  solid  body,  one  representing  the  image 
seen  by  the  right  eye,  the  other  that  seen  by  the  left,  for  example,  the  drawing 
of  a  cube,  A,  B,  figure  479,  be  presented  to  corresponding  parts  of  the  two 
retinae,  as  may  readily  be  done  by  means  of  the  stereoscope,  the  mind  will 
perceive  not  merely  a  single  representation  of  the  object,  but  a  body  pro- 
jecting in  relief,  the  exact  counterpart  of  that  from  which  the  drawings  were 
made. 

Size  and  Distance.  The  estimation  of  the  size  of  an  object  and  its  distance 
away  from  the  observer  is  based  in  part  upon  the  visual  image  and  in  part 
upon  judgments  due  to  past  experience.  The  two  elements  are  inseparable 
and  mutually  dependent.  Thus,  a  lofty  mountain  many  miles  away  may 
subtend  the  same  visual  angle  as  a  small  hill  near  at  hand.     While  the  size 


zr 


Fig.   479. — Diagrams  to  Illustrate  how  a  Judgment  of  a  Figure  of  Three  Dimensions  is  Obtained. 


and  shape  of  the  two  images  may  be  identical,  yet  the  image  of  the  hill  near 
at  hand  is  more  distinct,  its  details  are  perceived,  and  its  outlines  are  sharper 
than  in  the  image  of  the  mountain.  If  the  atmosphere  be  charged  with 
moisture  or  with  dust,  the  image  of  the  mountain  will  be  still  more  indistinct 
and  dim.  From  previous  experiences  we  have  learned  that  the  dimness  and 
indistinctness  of  the  one  and  the  definiteness  of  the  other  are  associated  with 
distance. 

If  two  objects  are  very  near  at  hand  then  there  will  be  a  difference  in 
the  convergence  of  the  two  eyes  in  binocular  vision.  It  is  now  well  known 
that  the  ocular  muscles  are  possessed  of  a  very  delicate  muscle  sense.  This 
muscle  sense  leaves  the  impression  which  enables  us  to  judge  that  the  one 
object  is  nearer  and  the  other  farther.  In  the  common  and  familiar  objects 
about  us  we  have  from  long  experience  and  intimate  contact  learned  their 
actual  size  and  the  character  of  the  retinal  image  formed  at  definite,  but  known 
distances.  When  such  an  object  forms  an  image  of  the  common  size  and 
usual  distinctness  on  the  retina,  the  judgment  as  to  its  distance  is  quickly 
made. 

In  the  case  of  unknown  objects  which  are  associated  with  known  ob- 
jects, the  judgment  of  the  size  and  distance  of  the  latter  is  used  in  forming 


LABORATORY  EXPERIMENTS  ON  THE  SENSE  ORGANS      669 

a  judgment  of  the  size  and  distance  of  the  former  by  comparison.  Many 
visual  deceptions  are  based  on  these  comparisons,  a  fact  that  is  often  taken 
advantage  of  by  photographers.  It  is  also  well  known  that  people  living  in 
a  moist,  hazy  climate  are  utterly  unable  accurately  to  estimate  distances 
when  suddenly  transferred  to  a  clear  mountain  climate. 

LABORATORY  DIRECTIONS  FOR  EXPERIMENTS  ON  THE 
SENSE  ORGANS. 

i.  Touch.  Use  the  small  compasses  with  rounded  tips  provided 
for  the  purpose,  and  determine  the  power  of  localization  of  the  sense  of  touch 
as  follows:  Have  the  person  observed  close  his  eyes,  then  touch  different 
parts  of  the  skin,  of  the  hand,  arm,  face,  neck,  etc.,  and  let  the  observed  one 
announce  the  exact  point  touched. 

The  localization  can  also  be  determined  by  touching  two  points  on  the 
skin  with  the  points  of  the  compasses  separated  by  varying  distances.  Ex- 
amine especially  the  skin  on  the  forearm,  on  the  back  of  the  hand,  on  the 
palm  of  the  hand,  the  tips  of  the  fingers,  and  at  different  points  on  the  face, 
including  the  lips  and  tip  of  the  tongue.     Touch  these  regions  of  the  skin 


Fig.  480. — Aristotle's  Experiment. 

with  either  one  or  with  two  points  of  the  compasses,  and  allow  the  person 
observed  to  announce  results,  drawing  your  conclusions  according  to  the 
principle  of  trial  and  error.  Make  a  table  showing  the  power  of  local  dis- 
crimination in  the  different  regions. 

2.  Aristotle's  Touch  Experiment.  Roll  the  tips  of  the  middle  and 
index  fingers  over  a  marble  and  note  that  the  sensation  from  the  two  fingers 
is  interpreted  as  that  of  a  single  object.  Now  cross  the  fingers  and  repeat 
the  experiment.     This  time  there  is  the  sensation  of  touching  two  spheres. 

3.  Temperature  Sensations.  It  is  a  common  experience  that  the 
hand  brought  in  the  neighborhood  of  a  warm  or  a  cold  object  develops  the 


670 


THE    SENSES 


sensation  of  warmth  or  cold.  Examine  a  given  small  area  of  the  back  of 
the  hand  with  the  thermoesthesiometer.  Certain  points  will  give  stronger 
sensation  of  heat  than  others.  Map  these  out  carefully.  Examine  the  same 
area  for  the  cold.  A  large  number  of  cold  spots  will  be  found  and  thev  will 
not  coincide  with  the  warm  spots,  figure  421. 

The  stimulation  for  the  hot  and  cold  spots  does  not  depend  upon  the 
absolute  temperature,  but  on  the  relative  temperature.     Insert  the  hand  in 


Fig.  481. — Localization  of  Taste.     Bitter ;  acid ;  salt, ;  sweet ;    T,  tonsils; 

FC,  foramen  cecum;    CF,  circumvallate  papillae;    FP,  fungiform  papillae.      (Hall.) 


water  that  feels  lukewarm.  Place  the  same  hand  in  a  cup  of  quite  warm  water 
for  a  moment,  then  reinsert  it  in  the  lukewarm  water.     This  will  now  feel  cold. 

4.  Sensations  of  Taste.  The  distribution  of  taste  organs  in  the 
tongue  is  shown  in  figure  481.  Examine  your  own  tongue  for  organs  of 
sweet,  acid,  saline,  and  bitter,  using  solutions  of  1  to  2  per  cent  salt,  10  per 
cent  sugar,  2  to  5  per  cent  acid,  5  per  cent  acetic  acid,  and  0.1  per  cent  quinine. 

Wipe  the  tongue  dry  and  apply  the  solution  named  from  the  tip  of  a  glass 
rod.  The  best  form  of  rod  is  about  15  cm.  long  by  0.5  cm.  in  diameter,  and 
has  one  end  drawn  out  to  a  slender  pencil-shaped  tip  and  of  a  size  which 
will  suspend  a  very  small  drop.  Too  large  a  drop  diffuses  over  too  great  an 
area  of  the  tongue.  Occasionally  small  crystals  of  sugar,  salt,  etc.,  give  more 
satisfactory  results. 

Perform  the  experiments  on  yourself  before  a  mirror  and  map  the  re- 
sults as  shown  in  figure  481. 

If  the  experiments  are  done  with  care  certain  papillae  will  be  found  which 
give  one  or  two  of  the  taste  sensations,  but  not  all. 

■J.  Sensations  of  Smell.      Quantitative   experiments  on  the   sense 


THE    LIMITS    OF    THE    .SENSE    OF     HEARING  671 

of  smell  are  difficult  to  determine.  Inhale  vapor  of  ammonia  so  dilute  that 
it  can  just  be  detected.  Note  that  the  sensation  is  strongest  at  the  moment 
of  drawing  the  vapor  into  the  nostril.  Fill  the  nostrils  with  the  diluted  vapor 
and  close  the  external  opening;  the  sensation  quickly  disappears.  Keeping 
the  nostrils  closed,  walk  into  the  open  air,  then  inhale  fresh  air.  At  the 
moment  of  the  inhalation  of  fresh  air  the  ammonia  is  again  perceptible. 
Repeat  with  bergamot,  rose  water,  etc. 

6.  The  Limits  of  the  Sense  of  Hearing.  Use  a  set  of  tuning  forks 
for  the  purpose,  and  determine  the  lowest  vibration  per  second  which  can  be 
perceived  as  sound.     Determine  the  highest  limits  in  the  same  way. 

7.  Acuteness  of  the  Sense  of  Hearing.  Listen  to  the  vibrations 
of  a  tuning  fork,  or,  better,  to  the  ticking  of  a  watch  which  is  moved  back  and 
forth  from  the  ear.  Measure  the  distance  at  which  it  can  just  be  distinguished. 
This  experiment  should  be  performed  with  the  person  blindfolded,  and  ex- 
traneous noise  should,  of  course,  be  suppressed. 

8.  Refraction.  Light  passes  out  from  a  luminous  point  in  straight 
lines  so  long  as  the  line  of  propagation  is  in  a  medium  of  uniform  density. 
If  the  rays  pass  form  a  transparent  medium  of  one  density  into  a  second 
medium  of  different  density,  they  will  usually  be  turned  out  of  their  course,  or 
refracted.  If  the  rays  enter  the  second  medium  at  right  angles  to  its  surface, 
they  will  continue  in  straight  lines,  but  if  they  enter  at  any  other  angle  they 
will  be  refracted.  If  the  second  medium  is  denser  than  the  first,  the  rays  will 
be  refracted  toward  the  perpendicular;  if  it  is  less  dense,  away  from  the  per- 
pendicular. 

Use  a  Hall's  refraction-measuring  apparatus  (constructed  of  a  carpenter's 
try  square).  Adjust  it  in  a  water-pan,  and  fill  to  the  exact  level  with  clear  water. 
Clamp  a  rule  to  the  vertical  limb  of  the  apparatus  at  an  angle  with  the  axial 
point  of  the  instrument.  Read  the  horizontal  scale  of  the  instrument  along  the 
edge  of  the  clamped  rule.  Remove  the  instrument  from  the  pan,  using  care 
not  to  disturb  the  adjustment  of  the  ruler,  and  construct  the  angle  of  refrac- 
tion on  coordinate  paper.  Determine  the  relation  of  the  angle  of  incidence 
and  of  refraction,  and  compute  the  refractive  index  of  the  water,  the  air 
having  a  refractive  index  of  one. 

Repeat  the  determination  using  a  block  of  glass. 

9.  To  Determine  the  Refractive  Power  of  a  Convex  Lens.  Use  a 
meter  stick  which  is  provided  with  a  movable  diaphragm  or  screen,  and  a 
holder  for  a  lens.  Measure  the  focal  distance  of  lens  number  i  as  furnished 
from  the  optical  set.  Put  the  lens  in  its  holder  and  focus  the  image  of  the 
sun  or  of  an  electric  bulb  on  the  screen,  moving  the  screen  back  and  forth 
until  the  sharp  focus  is  determined.  If  the  lens  is  accurately  ground,  the 
focus  will  be  at  a  distance  of  one  meter,  which  is  the  refractive  power  of  a 
one-diopter  lens,  hy  definition.  In  the  same  way  determine  the  refractive 
power  of  lenses  numbers  2,  3,  and  4. 


672  THE    SENSES 

Construct  the  path  of  the  light  in  the  formation  of  the  image  in  these  cases. 

Tf  the  measurement  in  the  above  case  is  made  through  two  parallel  open- 
ings or  diaphragms  about  5  mm.  in  diameter  each,  and  separated  by  4  or 
5  mm.,  the  point  of  focus  can  be  more  accurately  determined  (see  Scheiner's 
experiment,  No.  14.)  Construct  the  mathematical  figure  showing  the 
course  of  both  cones  of  rays  in  this  test. 

10.  Determination  of  Near  and  Far  Limits  of  Vision.  Support  a 
meter  stick  in  a  horizontal  position  at  a  comfortable  level  for  the  eye.  Mount 
a  needle  in  a  cork  and  set  it  on  the  meter  stick  about  25  cm.  in  front  of  the 
eye.  Make  two  pin-holes  in  a  card  at  a  distance  of  about  2  mm.  from  each 
other.  Hold  this  card  with  the  pin-holes  close  in  front  of  one  eye,  and  bring 
the  eye  up  to  the  end  of  the  meter  stick;  cover  the  other  eye.  Observe  that 
when  the  needle  is  brought  nearer  and  nearer  to  the  eye,  at  a  certain  distance 
it  becomes  double.  Determine  this  distance  very  accurately.  It  is  the  near- 
point  of  accommodation  for  the  right  eve.  Make  the  same  determination  for 
the  left  eye. 

Hold  the  punctured  card  in  front  of  the  right  eye,  and  move  the  needle 
(it  is  better  to  use  something  larger)  farther  and  farther  away  until  it  becomes 


Fig.   482. — Diagram  of  Experiment  to  Ascertain  the  Minimum  Distance  of  Distinct  Vision. 

again  double,  if  it  does  so.  This  is  the  jar-point  0}  accommodation.  In 
normal  eyes  there  is  no  far  limit.  In  practice  an  eye  that  has  no  far  limit 
under  twenty  feet  is  considered  normal.  This  test  should  be  made  on  each 
eye. 

11.  Inverted  Image  on  the  Retina.  Dissect  off  a  segment  of  the 
sclerotic  of  a  fresh  ox  eye,  or  use  a  fresh  eye  from  an  albino  rabbit.  Make 
a  tube  of  black  paper  of  the  size  of  the  eye,  and  insert  the  eye  in  one  end, 
with  the  cornea  directed  into  the  tube.  In  the  dark  room  examine  the  image 
of  the  candle  flame  as  formed  on  the  retina  of  the  eye  in  the  tube.  In  a 
favorable  experiment,  a  clear  inverted  image  of  the  candle  can  be  seen  on 
the  retina  through  the  semi-transparent  membranes  of  the  eye.  The  same 
experiment  can  be  demonstrated  with  the  camera,  or  with  a  small  lens,  using 
a  ground-glass  plate  to  make  the  image  more  apparent. 

12.  Spherical  Aberration.  In  physical  optics  it  is  found  that  it  is 
difficult   to   grind   lenses  so  that   they  will   refract  equally  in  the   center  or 


CHROMATIC    ABERRATION  673 

optical  axis  and  in  the  periphery.  Unequal  refraction  of  these  two  regions 
is  called  spherical  aberration.  It  is  corrected  in  optics  by  diaphragms  which 
shut  out  the  light,  either  from  the  borders  of  the  lens  or  from  its  center.  The 
former  method  is  used  in  the  eye.  To  demonstrate  Spherical  Aberration,  look 
at  an  object  two  meters  from  the  eye,  such  as  part  of  the  window.  Pass  a 
card  across  the  eye  until  the  light  enters  only  at  the  margin  of  the  pupil, 
i.e.,  the  borders  of  the  lens.  It  will  be  found  that  the  object  is  no  longer  in 
focus  and  the  outlines  are  dim  and  diffused.  Normal  eyes  are  near-sighted 
for  the  rays  that  are  refracted  by  the  borders  of  the  lens. 

13.  Chromatic  Aberration.  Look  toward  the  borders  between  the 
sash  and  the  bright  light  of  an  open  window,  at  a  distance  of  twenty  feet  or 
more.  Use  the  right  eye  only.  Bring  a  card  across  the  pupil  approaching 
from  the  side  of  the  light  until  the  eye  is  almost  covered  with  the  card. 
The  window  sash  will  seem  to  have  a  blue-violet  fringe.  If  the  card  is 
brought  across  from  the  opposite  side,  the  sash  will  have  a  reddish-yellow 
fringe. 

Make  a  cross  of  two  strips  of  Bradley's  pure  color  paper,  one  red  and  the 
other  blue,  on  a  black  surface.  When  held  at  the  proper  distance  the  red 
appears  nearer  than  the  blue.  This  phenomenon  is  brought  out  more  strongly 
by  covering  the  colored  papers  with  very  thin  white  tissue  paper.  The 
judgment  of  distance  is  based  on  the  effort  of  accommodation  which  is 
greater  for  the  red  than  for  the  blue  and  violet  rays. 

14.  Scheiner's  Experiment.  Use  two  needles  on  corks,  the  method 
described  in  experiment  i,  placing  one  at  a  distance  of  20  cm.,  and  the  other 
about  60  cm.  from  the  eye.  Use  only  the  right  eye,  look  through  two  pin- 
holes in  a  card  at  the  far  needle.  The  near  needle  will  appear  double,  but 
the  images  will  be  somewhat  blurred.  While  looking  at  the  far  needle,  bring 
a  cardboard  across  the  right  hole,  note  that  the  left  image  of  the  near  needle 
disappears,  and  vice  versa.  If  one  accommodates  for  the  near  needle,  the  far 
needle  appears  double,  and  upon  covering  the  right  hole  with  the  card  the 
right  image  of  the  far  needle  disappears.  This  is  known  as  Scheiner's  Ex- 
periment.    Construct  a  diagram  to  explain  these  phenomena. 

15.  Purkinje-Sanson's  Images.  Examine  the  eye  of  another  person  in 
a  dark  room  as  follows :  With  the  observing  eye  focus  for  a  far  object,  let  the 
observer  hold  a  candle  slightly  to  one  side  of  the  axis  of  vision  and  about 
one  foot  from  the  eye.  If  the  observer  looks  into  the  other  eye  from  the  side 
opposite  the  candle,  he  will  be  able  to  see  three  reflected  images,  figures  457 
and  458.  One,  from  the  anterior  surface  of  the  cornea,  is  bright  and  dis- 
tinct, and  of  medium  size  and  erect.  In  the  middle  of  the  pupil  there  will  be 
a  second  image,  larger  and  quite  dim.  This  is  a  reflection  from  the  front 
of  the  lens.  The  third  image,  reflected  from  the  posterior  surface  of  the  lens, 
will  seem  to  be  farther  back  in  the  eye,  quite  small  and  inverted.  These 
images  can  all  three  be  seen  at  once  with  careful  adjustment  of  the  relative 

43 


674 


THE     SENSES 


positions  of  the  candle  and  the  observer,  with  reference  to  the  axis  of 
vision  of  the  eye  observed. 

If  the  observer  protects  his  own  eye  from  the  direct  iight  of  the  candle 
by  a  blackened  cardboard  between  his  eye  and  the  candle,  and  asks  the 
observed  person  to  accommodate  now  for  near  objects;  now  for  far,  keeping 
the  axis  of  vision  constant,  he  will  be  able  to  note  that  the  middle  image, 
i.e.,  the  one  from  the  anterior  surface  of  the  lens,  changes  in  size  and  in  relative 
position  with  reference  to  the  other  two,  which  are  essentially  constant.  With 
near  accommodation  this  image  becomes  smaller  and  seems  to  move  toward 
the  image  from  the  cornea;  with  far  accommodation  it  becomes  larger  and 
appears  to  move  to  the  image  reflected  from  the  posterior  surface  of  the  lens. 
This  shows  that  the  act  of  accommodation  consists  in  a  change  in  the  con- 
vexity of  the  front  of  the  lens. 

16.  The  Phakoscope  of  Helmholtz.  This  classical  instrument  was 
invented  by  Helmholtz  to  demonstrate  the  act  of  accommodation,  as  out- 


Fig.   483. — Disc  of  Concentric  Lines  for  the  Astigmatic  Test. 


lined  in  the  second  paragraph  of  the  preceding  experiment.     Repeat  the 
preceding  experiment,  using  this  instrument  in  a  dark  room. 

17.  Astigmatism.  Astigmatism  is  a  term  used  to  describe  the  con- 
dition of  unequal  curvature  of  the  refracting  surfaces  of  the  eye  in  the 
different  meridia.  The  cornea  is  the  surface  which  usually  shows  the  greatest 
astigmatism.  This  defect  is  demonstrated  by  numerous  forms  of  astigmatic 
charts,  the  most  serviceable  of  which  are  the  barred-letter  test  type,  the  clock 
dial,  or  the  dials  shown  in  figure  463  or  483.  Hang  an  astigmatic  dial  at  a 
distance  of  six  meters  and  test  the  right  and  left  eyes  separately,  as  follows: 
When  the  vision  is  focussed  on  the  center  of  the  dial,  if  the  eye  is  normal, 
the  three  bars  in  each  radius  of  the  clock  dial  will  be  seen  with  equal  distinct- 
ness and  have  sharp  black  lines.  In  an  astigmatic  eye  one  or  more  of  these 
radii  will  appear  sharp  and  distinct,  while  the  other  will  appear  dim  and 


THE     BLIND     .SPOT  675 

indistinct,  the  relative  difference  depending  upon  the  degree  of  astigmatism. 
Note  the  meridian  of  astigmatism  in  the  right  and  left  eyes  separately.  Use 
the  test  set,  and  find  the  cylinder  necessary  to  correct  the  astigmatism  in  each 
eve  and  determine  its  meridian. 

Astigmatism  is  commonly  shown  by  the  presence  of  radii  when  one  looks 
at  the  stars  at  night,  or  by  the  ragged  outline  of  a  pin-hole  in  a  card,  when 
held  at  arm's  length  against  a  white  sky.     In  extreme  cases  outlines  like 


Fig.   484.— Diagram  for  Demonstrating  the  Blind  Spot. 

the  bars  in  the  window  sash  or  checks  in  clothing  may  be  distorted,  or  some 
of  the  lines  may  not  even  be  seen. 

18.  The  Blind  Spot.  Look  with  the  right  eye  at  the  spot  in  the  ac- 
companying figure  at  a  distance  of  about  20  to  25  cm.,  covering  the  left  eve. 
Hold  the  spot  in  the  line  of  direct  vision  and  move  the  book  to  and  from 
the  eye;  in  some  cases  it  is  necessary  to  rotate  the  book  slightly.  It  will  be 
found  that  the  cross  to  the  right  will,  at  a  certain  position,  completely  disappear. 
This  happens  when  its  image  falls  on  the  retina  directly  over  the  entrance  of 
the  optic  nerve,  which  has  no  visual  cells,  and  is,  therefore,  the  blind  spot. 


Fig.   485. — The  Blind  Spot  with  the  Eye  30  cm.  from  the  Paper. 

This  area  is  large  enough  to  cause  a  man  completely  to  disappear  at  a  dis- 
tance of  about  one  hundred  meters. 

Place  a  sheet  of  white  paper  at  a  distance  of  30  cm.  in  front  of  the  eye, 
holding  the  head  in  a  fixed  position  by  some  support;  look  with  the  right  eye 
at  the  top  of  the  cross  made  on  the  left  of  the  sheet  of  paper.  Covering  the 
sharpened  portion  of  a  lead  pencil  with  white  paper,  leaving  the  black  tip 
exposed,  move  this  pencil  across  the  paper  from  the  visual  center  to  the 
right.     At    a    certain    distance    the    black    lead    will    suddenly    disappear. 


G7(>  THE    SENSES 

Mark  this  point.  Continue  to  move  the  pencil  until  the  lead  reappears. 
Mark  this  point.  These  two  points  represent  the  limits  of  the  blind  spot  in 
the  horizontal  plane,  as  magnified  by  the  conditions  of  the  experiment.  Mark 
the  limits  in  the  other  meridians  in  the  same  manner.  Compute  from  the 
figures  obtained  the  exact  size  of  the  blind  spot  in  your  right  eye,  figure  485. 
Repeat  on  the  left  eye.  Usually  these  areas  are  not  symmetrical.  The  com- 
putation may  be  based  on  the  following  proportion:  a,  the  diameter  of  the 
mapped  blind  spot  is  to  the  distance  of  the  map  from  the  nodal  point  of  the 
eye,  x,  as  c,  the  distance  from  the  nodal  point  to  the  retina,  which  is  1.5  cm., 
is  to  x,  the  diameter  of  the  actual  blind  spot  in  the  retina,  x  varies  from 
1.5  to  3  or  more  mm.     a  :  b  :  :  c  :  x. 

19.  Relations  of  the  Size  of  the  Retinal  Image  to  Distance.  Com- 
pute the  size  of  the  retinal  images  of  familiar  objects  by  the  equation  given 
in  the  last  experiment.  Compute  the  size  of  the  image  formed  on  the  retina 
by  a  man  six  feet  tall  at  a  distance  of  100  feet.  Compute  the  size  of  the 
image  formed  by  a  tower  125  feet  tall  at  a  distance  of  575  feet. 

20.  Purkinje's  Shadows.  Stand  in  front  of  a  blackened  wall  in 
the  dark  room.  While  looking  toward  the  wall  with  the  right  eye  accom- 
modated for  distant  objects,  move  a  lighted  candle  back  and  forth  about 
10  to  20  cm.  to  the  right  of  the  eye  and  a  little  below  its  level.  Presently 
many  branching  shadows  will  be  seen  as  though  they  stood  in  space  in  front 
of  the  individual.  These  are  the  shadows  of  the  blood-vessels  cast  upon  the 
retina.  A  careful  examination  will  show  that  these  shadows  seem  to  con- 
verge to  a  point  to  the  right  of  the  center  of  vision  of  the  right  eye.  By  moving 
the  candle  up  and  down  or  from  side  to  side,  the  shadows  seem  also  to  move 
slightly.  Many  persons  can  readily  see  Purkinje's  figures  by  looking  through 
the  narrow  spaces  between  the  fingers  of  the  hand  moved  close  in  front  of 
the  eve,  when  the  vision  is  directed  toward  a  bright  sky.  One  can  demonstrate 
by  this  means  that  the  macula  is  free  from  blood-vessels,  since  the  pattern 
of  the  blood-vessels  around  the  borders  of  the  macula  is  very  readily  de- 
termined.    This  is  especially  true  if  there  is  slight  retinal  congestion. 

21.  Duration  of  the  Retinal  Image.  When  a  beam  of  light  falls 
upon  the  retina  for  an  instant  it  produces  a  stimulus  which  endures  for  a 
time  after  the  stimulus  is  removed.  This  interval  can  be  measured  by  the  proper 
mechanical  device.  Place  on  the  color  wheel  a  disc,  which  has  a  small  seg- 
ment cut  out  at  one  point  on  the  periphery.  Put  a  printed  page  behind  the 
segment  with  the  observer  standing  in  front.  Rotate  the  segment  faster  and 
faster  until  the  printed  page  is  seen  continuously.  At  this  point  the  visual 
image  made  at  one  revolution  of  the  disc  lasts  until  the  next  impression  on 
the  same  spot.  The  speed  of  the  revolution  of  the  color  wheel  can  be  measured 
by  attaching  an  electric  contact  key  and  signal  magnet  to  the  disc  wheel  and 
measuring  the  rate  of  interruptions  against  the  known  vibrations  of  a  tuning 
fork.     The  same  phenomenon  may  be  determined  by  placing  on  the  disc 


LIMITS   OF   THE    FIELD    OF   VISION  677 

two  complemental  colors  and  judging  the  speed  of  revolution  required  for 
complete  fusion. 

22.  Limits  of  the  Field  of  Vision.  The  limits  of  the  visual  field  are 
determined  by  direct  measurement  with  the  perimeter.  Set  the  person  whose 
retina  is  to  be  measured  in  a  comfortable  erect  position,  with  one  eye  at  the 
center  of  the  arc  of  the  perimeter  and  the  other  covered  by  an  eye-shade. 
The  observed  eye  must  be  fixed  on  the  center  of  the  field  of  vision,  and  care 
must  be  used  to  prevent  obstruction  of  the  field.  The  examination  is  made 
with  greatest  accuracy  by  bringing  an  object  into  the  field  of  vision  from  behind 
the  person  observed.  When  the  individual  examined  first  detects  the  presence 
of  the  object,  he  announces  it  and  the  angle  is  read  off  from  the  arc  of  the 
perimeter  and  recorded  on  the  chart  for  the  purpose.  These  readings  should 
be  made  in  about  twelve  radii.     They  should  be  made  for  each  eye. 

23.  Limits  for  the  Field  of  Vision  for  Color.  To  measure  the  limits 
of  the  field  of  vision  for  colors  one  should  proceed  as  in  the  preceding  experi- 
ment, except  that  small  squares  of  colored  papers  are  brought  into  the  field 
from  the  rear.  The  retina  should  be  mapped  for  red,  green,  yellow,  and  blue. 
Use  Bradley's  pure  color  papers.  Take  four  penholders  and  mount  on  the 
end  of  one  a  centimeter  square  of  red  paper,  on  the  others  green,  yellow,  and 
blue.  To  make  a  determination  bring  the  color  up  from  behind  and,  as  soon 
as  it  is  certainly  detected  and  announced,  remove  it  from  the  field  of  vision. 
Examine  the  eye  for  all  four  colors  at  one  sitting,  mixing  them  indeterminately 
in  the  individual  tests.  Occasionally  an  eve  will  be  found  which  exhibits  a 
well-marked  restriction  of  the  color  field,  though  the  individual  himself  may 
not  be  completely  color-blind. 

24.  Color-Blindness.  Make  an  examination  for  color-blindness, 
using  Holmgren's  colored  yarns.  Spread  the  yarns  out  on  a  table  in  the  best 
of  light.  Place  the  three  confusion  skeins  in  front  of  the  individual  to  be  ex- 
amined and  ask  him  to  match  them  quickly  from  the  skeins  on  the  table, 
paying  no  attention  to  lights  and  shades  of  the  same  color.  A  color-blind 
individual  will  confuse  colored  skeins,  most  usually  the  reds,  greens,  and  grays. 

25.  Color  Mixing.  Use  Bradley's  color  wheel  and  test  the  effect 
of  simultaneous  stimulation  of  the  retina  with  two  or  more  colors,  by  placing 
on  the  wheel  two  or  more  colored  discs,  rotating  the  wheel  at  a  speed  sufficient 
to  cause  complete  fusion.  The  sensation  produced  by  two  colors  applied 
simultaneously  will  be  entirely  different  from  that  produced  by  either  alone. 
Red  and  green  (or  greenish  blue),  when  mixed  in  the  proper  proportion,  pro- 
duce a  sensation  of  gray.  The  same  effect  may  be  had  from  yellow  and  blue, 
orange  and  violet,  or  any  of  the  complementary  colors  chosen  according  to 
the  geometrical  color  table,  figure  473.  By  mixing  three  colors,  red,  green, 
and  violet,  in  the  proper  proportion  one  can  produce  a  sensation  almost  the 
same  as  that  produced  by  white  light. 

26.  Color  After-images.      Color  after-images  can  be  demonstrated 


678  THE     SENSES 

by  looking  continuously  at  the  center  of  one  of  the  primary  colors  of  Bradley's 
color  charts  against  a  white  or  gray  wall  until  there  is  apparent  fatigue, 
then  suddenly  removing  the  chart.  An  after-image  of  approximately  the 
complementary  color  will  appear  in  the  course  of  a  few  seconds.  Occasionally 
these  images  are  very  vivid.  The  experiments  are  brilliant  if  performed  in 
the  dark  room,  using  colored  gelatin  screens  through  which  an  intense  light 
shines.  "When  the  light  is  turned  off,  a  brilliant  after-image  of  the  comple- 
mentary color  appears. 

27.  Retinoscopy.  Use  the  ordinary  small  ophthalmoscope  and  ex- 
amine the  retina  of  the  eye  of  a  cat  or  rabbit.  Dilate  the  eye  by  the  use  of 
atropine.  Place  the  animal  whose  eye  is  to  be  examined  on  a  support  in 
front  of  a  bright  but  uniform  light  (an  Argand  burner).  Reflect  the  light 
from  the  mirror  of  the  ophthalmoscope  through  the  pupil  into  the  retinal  cup 
of  the  animal.  Usually  the  ophthalmoscope  has  to  be  fccussed  for  a  cat's 
retina.  When  a  good  light  is  secured,  the  retinal  cup  will  appear  as  a  bril- 
liantly colored  disc,  with  the  branching  blood-vessels,  and  usually  with  some 
brilliant  bluish-green  pigment  in  the  lower  portions  of  the  retinal  disc. 

After  some  practice  on  the  cat  or  the  rabbit,  the  student  should  examine 
the  retina  of  one  of  his  mates,  preferably  an  eye  that  has  an  unusually  wide 
pupil.  In  some  cases  a  light  dosage  of  homatropine  may  be  used  on  one  eye. 
This  will  dilate  the  pupil  and  the  examination  will  be  much  easier. 

Students  are  not  recommended  to  use  atropine  unless  under  conditions 
which  permit  the  eye  to  rest  for  two  or  three  days  following. 

28.  Visual  Acuity.  The  visual  acuity  of  the  eye  should  be  tested 
first  for  the  right  eye,  then  for  the  left.  Hang  a  test  chart  at  a  distance  of 
twenty  feet,  so  that  its  disc  is  well  illuminated,  and  allow  the  individual  tested 
to  read  off  the  letters  on  the  chart,  beginning  with  the  larger  ones  at  the  top. 
The  letters  on  this  chart  are  constructed  on  the  basis  of  a  visual  angle  of  five 
degrees.  When  the  letters  marked  "twenty  feet"  or  "six  meters  "  represent 
the  limit  of  accurate  identification,  the  visual  acuity  is  said  to  be  1,  or 
normal.  If  the  line  marked  "  thirty  feet "  is  the  limit,  then  the  acuity  is  one 
and  a  half;    if  "fifteen  feet,"  then  the  visual  acuity  is  three-fourths,  etc. 

If  the  eyes  tested  are  astigmatic,  or  have  other  optical  defects,  these  must 
first  be  corrected  before  testing  for  visual  acuity. 

29.  The  Test  Set.  The  student  is  recommended  to  close  the  ex- 
periments on  the  eye  by  fitting  glasses  for  himself  and  at  least  two  others. 
He  should  correct  for  the  defects  that  have  been  revealed  in  the  preceding 
experiments,  especially  for  astigmatism;  myopia,  or  hypermetropia;  and 
presbyopia.     Of  course  each  eye  must  be  tested  and  fitted  separately. 


CHAPTER  XVI 

THE   REPRODUCTIVE    ORGANS 

THE  REPRODUCTIVE  ORGANS  OF  THE  MALE. 

The  male  reproductive  organs  comprise  the  Testes,  the  Wis  Deferens, 
the  Vesicula  Seminalis,  the  Prostate  Gland,  and  the  Penis. 

The  Testes.  The  testes  consist  of  two  parts,  i,  the  testicle,  which 
is  covered  by  the  tunica  vaginalis  and  secretes  the  germinal  cells,  and  2,  the 
conducting  tubules,  which  compose  the  epididymis  and  vas  deferens. 

The  testicle  is  divided  by  connective-tissue  septa  into  lobules,  the  tubuli 
seminiferi.  Each  tubule  is  limited  by  a  membrana  propria  on  which  rests 
the  germinal  epithelium. 

On  the  approach  of  sexual  maturity  the  process  of  spermatogenesis  begins. 


mm* 


Till  mm 


Fig.  486. 


Fig.  487. 


Fig.  486. — Plan  of  a  Vertical  Section  of  the  Testicle,  Showing  the  Arrangement  of  the  Ducts. 
The  true  length  and  diameter  of  the  ducts  have  been  disregarded,  a,  a,  Tubuli  seminiferi  coiled 
up  in  the  separate  lobes;  b,  tubuli  recti  or  vasa  recta;  c,  rete  testis;  d,  vasa  deferentia  ending  in 
the  coni  vasculosi;  /,  e,  g,  convoluted  canal  of  the  epididymis;  h,  vas  deferens;  /,  section  of 
the  back  part  of  the  tunica  albuginea;  i,  i,  fibrous  processes  running  between  the  lobes;  s,  me- 
diastinum. 

Fig.  487- — Vertical  Section  through  the  Wall  of  the  Tubules  of  Epididymis.  X  700  (Kol- 
liker. )  b.  Connective  tissue  and  smooth  muscle  cells;  c,  basal  layer  of  epithelial  cells;  f,  high 
columnar  cells;   p,    pigment  granules  in  columnar  cells;   c,  cuticula;   //.cilia. 

The  germinal  cells  multiply  rapidly,  and,  by  a  complex  series  of  mitotic  divisions 
or  stages,  form  ultimately  the  male  reproductive  cells,  or  sperm  cells. 

The  important  stages  in  order  are:  archispermiocyte,  spermatogonia, 
primary  and  secondary  spermatocytes,  spermatids,  and  spermatozoa.  The 
spermatogonia  stage  is  the  stage  of  rapid  multiplication;  the  spermatocyte, 
that  of  maturation,  comparable  to  the  maturation  stage  of  the  ovum. 

679 


680 


THE     REPRODUCTIVE    ORGANS 


The  sperm  cells  are  the  essential  male  reproductive  cells.  Each  sperma- 
tozoan  consists  of  a  minute  oval  head,  a  middle  piece,  and  a  tail.  The  head 
is  4  /j-  by  2.5  fi.  The  middle  piece  and  tail  are  about  50  to  60  p.  long. 
Sperm  cells  possess  the  power  of  flagellate  movement. 

The  Vas  Deferens.  This  is  the  single  duct  proceeding  from  each 
testicle  to  join  its  fellow  at  the  base  of  the  bladder.     Each  has  an  ampulla  or 


■Spd 


Fig.  488. — Later  Stages  in  Spermatogenesis  of  the  Bull,  spg.r,  Reserve  spermatogonium; 
spg,  spermatogonium;  spc.g,  spermatocyte  in  late  synapsis  stage;  spc.i,  spermacyte  in  stage  just 
preceding  the  maturation  divisions;  spd,  spermatids  in  advanced  stage  of  histogenesis,  with 
heads  deeply  embedded  in  Sertoli  cell.     Highly  magnified.     (After  Schoenfeld.) 


enlargement  just  before  it  unites  with  its  fellow.     The  vas  deferens  has  muscu- 
lar walls  and  is  lined  with  ciliated  epithelial  cells. 

The  Vesiculae  Seminales.  The  seminal  vesicles  have  the  appear- 
ance of  outgrowths  from  the  base  of  the  vasa  deferentia.  Each  vas  deferens, 
just  before  it  enters  the  prostate  gland,  through  part  of  which  it  passes  to 
terminate  in  the  urethra,  gives  off  a  side  branch  which  bends  back  from  it  at 
an  acute  angle.     This  branch,  dilating,  variously  branching,  and  pursuing  in 


THE     PENIS 


681 


both  itself  and  its  branches  a  tortuous  course,  forms  the  vesicula  seminalis. 
Each  vesicula  is  a  single-branching  convoluted  and  sacculated  tube. 

The  structure  resembles  closely  that  of  the  vasa  deferentia. 

The  Penis.  The  penis  is  attached  to  the  symphysis  pubis  by  its 
root.     It  is  composed  of  three  long,  more  or  less  cylindrical  masses  enclosed 


Fig.  489. — Section  of  a  Tubule  of  the  Testicle  of  a  Rat,  to  Show  the  Formation  of  the  Sperma- 
tozoa, a,  Spermatozoa;  b,  seminal  cells;  c,  spermatoblasts,  to  which  the  spermatozoa  are  still 
adherent;  d,  aiembrana  propria;   e,  fibro-plastic  elements  of  the  connective  tissue.     (Cadiat.) 


Fig.  490. — Dissection  of  the  Base  of  the  Bladder  and  Prostate  Gland,  Showing  the  Vesiculae 
Seminales  and  Vasa  Deferentia.  a.  Lower  surface  of  the  bladder  at  the  place  of  reflection  of  the 
peritoneum;  b,  the  part  above  covered  by  the  peritoneum;  i,  left  vas  deferens,  ending  in  e,  the 
ejaculatory  duct;  the  vas  deferens  has  been  divided  near  i,  and  all  except  the  vesical  portion 
has  been  taken  away;  s,  left  vesicula  seminalis  joining  the  same  duct;  s,s,  the  right  vas  deferens 
and  right  vesicula  seminalis.  which  has  been  unraveled;  p,  under  side  ot  the  prostate  gland;  »», 
part  of  the  urethra;   u,  u,  the  ureters  (cut  short),  the  right  one  turned  aside.      (Haller.) 


682 


THE     REPRODUCTIVE     ORGANS 


in  remarkably  firm  fibrous  sheaths.  Two,  the  corpora  cavernosa,  are  alike 
and  are  firmly  joined  together.  They  receive  below  and  between  them  the 
third  part,  or  corpus  spongiosum.  The  urethra  passes  through  the  corpus 
spongiosum.  The  enlarged  extremity,  or  glans  penis,  is  continuous  with  the 
corpus  spongiosum.  Cowper'i  glands  are  at  its  base,  and  their  ducts  open 
into  the  base  of  the  urethra. 

The  Prostate  Gland.  The  prostate  is  .situated  at  the  neck  of  the 
urinary  bladder,  ami  encloses  the  base  of  the  urethra.  The  prostate  is  made 
up  of  small  compound  tubular  glands  embedded  in  an  abundance  of  mus- 


Fig.   4qi. — Human  Spermatozoa  (after  Retzius).     A,  Side  view;    B,  front  view. 


cular  fibers  and  connective  tissue.  The  glandular  substance  consists  of 
numerous  small  saccules,  opening  into  elongated  ducts,  which  unite  into  a 
smaller  number  of  excretory  ducts.  The  acini  of  the  upper  part  of  the  prostate 
are  small  and  hemispherical,  in  the  middle  and  lower  parts  the  tubes  are 
longer  and  more  convoluted.  The  ducts,  twelve  to  twenty  in  number,  open 
into  the  urethra.  They  are  lined  by  a  layer  of  columnar  cells,  beneath  which 
is  a  layer  of  small  polyhedral  cells. 

The  muscular  tissue  of  the  prostate  not  only  forms  the  chief  part  of  the 
stroma  of  the  gland,  but  also  forms  a  continuous  layer  inside  the  fibrous  sheath, 
as  well  as  a  layer  surrounding  the  urethra  continuous  with  the  sphincter  of 
the  bladder. 

The  Seminal  Fluid.  The  sperm  cells  of  the  testes  are  joined  on  their 
way  to  the  exterior  by  the  fluids  secreted  by  the  mucous  lining  of  the  various 
tubules  and  glands.     'Of  the  fluids  the  chief  ones  are  the  secretions  of  the 


THE     REPRODUCTIVE     ORGANS     OF    THE     FEMALE 


6'83 


seminal  vesicles,  of  the  prostate  gland,  and  of  Cowper's  glands.  The  sperm 
cells  and  the  secretions  together  constitute  the  seminal  fluid. 

After  the  period  of  puberty  the  seminal  fluid  is  secreted  constantly  but 
slowly,  except  under  sexual  excitement.  It  is  ordinarily  received  into  the 
seminal  vesicles,  whence  it  is  expelled  at  the  time  of  coitus.  In  celibates  the 
seminal  fluid  may  at  times  escape  in  small  quantity  into  the  urethra  to  be 
washed  away  by  the  urine,  or  periodic  reflex  emissions  may  occur.  The 
seminal  vesicles  contribute  a  secretion,  as  well  as  a  vesicle  to  receive  the  sperm. 

The  secretion  of  the  seminal  vesicles  and  that  of  the  prostate  gland  are 
in  some  way  concerned  in  maintaining  the  activity  and  prolonging  the  life  of 
the  spermatozoa.  These  cells  remain  alive  in  the  fluid  for  as  much  as  forty- 
eight  hours  after  removal  from  the  body,  and  remain  alive  quite  indefinitely 
in  the  vesicles  in  the  body.  The  secretions  have  been  proven  necessary  to 
the  life  and  function  of  the  spermatozoa  by  the  results  of  operations  in  which 
the  seminal  vesicles  and  the  prostate  were  removed,  whereby  the  animal  be- 
came sterile. 

THE  REPRODUCTIVE  ORGANS  OF  THE  FEMALE. 

The  female  genital  organs  consist  of  the  ovaries,  the  Fallopian  tubes,  the 
uterus,  and  the  vagina. 

The  Ovaries.      The  ovaries  are  paired  bodies,  situated   in  the  cav- 


Fig.  492. — Diagrammatic  View  of  the  Uterus  and  Its  Appendages,  as  Seen  from  Behind.  The 
uterus  and  upper  part  of  the  vagina  have  been  laid  open  by  removing  the  posterior  wall;  the 
Fallopian  tube,  round  liagment,  and  ovarian  ligament  have  been  cut  short,  and  the  broad  liga- 
ment removed  on  the  left  s,de.  u.  The  upper  part  of  the  uterus;  c,  the  cervix  opposite  the  os  in- 
ternum; the  triangular  shape  of  the  uterine  cavity  is  shown,  and  the  dilatation  of  the  cervical 
cavity  with  the  rugae  termed  arbor  vitas;  v,  upper  part  of  the  vagina;  od.  Fallopian  tube  or  ovi- 
duct; the  narrow  communication  of  its  cavity  with  that  of  the  cornu  of  the  uterus  on  each  side  is 
seen;  /,  round  ligament;  lo,  ligament  of  the  ovary;  o,  ovary;  i,  wide  outer  part  of  the  right  Fal- 
lopian tube;  fi,  its  fimbriated  extremity;  po,  parovarium;  h,  one  of  the  hydatids  frequently  found 
connected  with  the  broad  ligament,      i.      (Allen  Thomson.) 


ity  of  the  pelvis,  and  adherent  to  the  posterior  surface  of  the  broad  ligament. 
The  border  of  the  ovary  is  called  the  hilum,  and  it  is  at  this  point  that  the 


684 


THE     REPRODUCTIVE     ORGANS 


blood-vessels  and  nerves  enter  it.  Each  ovary  is  about  4  cm.  long,  2  cm.  wide, 
and  1.25  cm.  thick.     It  is  supported  by  the  suspensory  ligament. 

The  internal  structure  of  the  ovary  consists  of  a  peculiar  soft  fibrous  con- 
nective tissue,  stroma,  abundantly  supplied  with  blood-vessels.  The  surface 
of  the  ovary  is  covered  with  cubical  epithelium.  Embedded  in  the  stroma  in 
various  stages  of  development  are  numerous  minute  follicles  or  vesicles,  the 
Graafian  follicles,  containing  the  ova,  figure  494.  They  are  small  and  numer- 
ous near  the  surface  of  the  ovary,  either  arranged  as  a  continuous  layer,  as 
in  the  cat  or  rabbit,  or  in  groups,  as  in  the  human  ovary.  Nearer  the  center 
are  large  and  fully  developed  follicles. 

Each  follicle  has  an  external  membranous  envelope,  or  membrana  propria, 
which  is  lined  with  a  layer  of  nucleated  cells,  forming  a  kind  of  epithelium 


Fig.  493. — Diagrammatic  Section  of  the  Ovary,  Showing  its  Cortical  or  Ovigenous  Layer,  Formed 
of  Ovisacs  in  Various  Stages  of  Evolution.  (Duval.)  A,  A,  A,  Primordial  ovisacs;  B,  B,  B,  ovisacs 
further  developed;  C,  ovisac  approaching  maturity;  D,  ripe  ovisac  with  its  proligerous  disc  (DP) 
containing  the  ovum;  MG,  membrana  granulosa;  H,  hilum  of  ovary. 


or  internal  tunic,  and  named  the  membrana  granulosa.  The  cavity  of  the 
follicle  contains  the  ovum  enclosed  in  a  very  delicate  membrane.  The  large 
spherical  nucleus  contains  one  or  more  nucleoli.  The  nucleus  is  known  as 
the  germinal  vesicle,  and  the  nucleolus  as  the  germinal  spot. 

The  human  ovum  measures  about  0.2  mm.  in  diameter.  Its  external 
investment,  or  the  zona  pellucida,  or  vitelline  membrane,  is  a  transparent 
membrane,  about  10  /*  in  thickness,  which  under  the  microscope  appears 
as  a  bright  ring,  figure  495.  The  ovum  itself  has  the  characteristic  structure 
of  the  typical  cell,  with  the  exception  that  its  cytoplasm  is  filled  with  numerous 
yolk  granules.  The  larger  granules  cr  globules,  which  have  the  aspect  of 
fat-globules,  are  in  greatest  number  at  the  periphery  of  the  yolk. 

The  nucleus,  or  germinal  vesicle,  is  about  0.05  mm.  in  diameter.  The 
vesicle  is  of  greatest  relative  size  in  the  smallest  ova. 

The  Graafian  follicles  are  formed  in  the  following  manner:    The  em- 


THE    OVARIES 


685 


bryonic  ovary  is  covered  with  short  columnar  cells,  or  the  so-called  germinal 
epithelium.  The  cells  of  this  layer  undergo  proliferation  so  as  to  form  several 
strata,  and  grow  into  the  ovarian  stroma  as  longer  or  shorter  columns  or  tubes. 
By  degrees  these  tubes  become  cut  off  from  the  surface  epithelium,  and  form 
cell  nests,  small  if  near  the  surface,  larger  if  in  the  depth  of  the  stroma.  The 
nests  increase  in  size  from  multiplication  of  their  cells.  Certain  cells  of  the 
germinal  epithelium  enlarge,  and  form  ova;  and  the  formation  of  ova  takes 
place  in  the  nests  within  the  stroma.  The  small  cells  of  a  nest  surround 
the  ova,  and  form  their  membrana  granulosa,  and  the  stroma  growing  up 
separates  the  surrounded  ova  into  so  many  Graafian  follicles. 

The  smallest  follicles  are  formed  at  the  surface,  and  make  up  the  cortical 


Downgrowths  of  epithelium 
Germinal  epithelium 


Ovum  with  its  investing  cells 


Stratum  granulosus 


Liquor  folliculi 
Discus  proligerus 

Fig.  494. — A,  Diagrammatic  Representation  of  the  Manner  in  which  the  Graafian  Follicles 
Arise  During  the  Development  of  the  Ovary.  B,  Diagram  Illustrating  the  Structure  of  a  Ripe 
Graafian  Follicle.      (Cunningham.) 


layer.  It  is  said  by  some  that  the  superficial  follicles  as  they  ripen  become 
more  deeply  placed  in  the  ovarian  stroma;  and,  again,  that  as  they  increase 
in  size,  they  make  their  way  toward  the  surface. 

When  the  Graafian  follicles  mature,  they  form  little  prominences  on  the 
exterior  of  the  ovary  covered  only  by  a  thin  layer  of  condensed  fibrous  tissue 
and  epithelium.  From  the  earliest  infancy,  and  through  the  whole  fruitful 
period  of  life,  there  appears  to  be  a  constant  formation,  development,  and 
maturation  of  Graafian  vesicles,  with  their  contained  ova.  Until  the  period 
of  puberty,  however,  the  process  is  comparatively  inactive.  But,  coincident 
with  the  other  changes  which  occur  in  the  body  at  the  time  of  puberty,  the 
ovaries  enlarge  and  become  very  vascular,  the  formation  of  Graafian  vesicles 
is  more  abundant,  the  size  and  degree  of  development  attained  by  them  are 
greater,  and  the  ova  are  capable  of  being  fertilized. 


686 


THE     REPRODUCTIVE    ORGANS 


The  Fallopian  Tubes,  or  Oviducts.  The  Fallopian  tubes  are  about 
to  cm.  in  length  and  extend  between  the  ovaries  and  the  upper  angles  of  the 
uterus.  At  the  point  of  attachment  to  the  uterus,  each  tube  is  very  narrow; 
but  in  its  course  to  the  ovary  it  increases  to  about  3  mm.  in  thickness.  At 
its  distal  extremity,  which  is  free  and  floating,  it  bears  a  number  of  -fimbria, 
one  of  which  is  longer  than  the  rest  and  is  attached  to  the  ovary.     The  canal 


1 ., 


Fig.  495. — Diagrammatic  Representation  of  a  Human  Ovum  and  Its  Coverings.  (Cunning- 
ham.) 

The  corona  radiata,  which  completely  surrounds  the  ovum',  is  represented  only  in  the  lower 
part  of  the  figure. 

1,  Corona  radiata;  5,  vitellus  or  yolk;  / 

2,  granular  layer;  6,  germinal  vesicle  (nucleus); 

3,  vitelline  membrane;  7,  germinal  spot  (nucleolus); 

4,  zona  pellucida  (oolemma);  8,  nuclear  membrane. 


of  the  tube  is  narrow,  especially  at  its  point  of  entrance  into  the  uterus.  Its 
other  extremity  is  wider  and  opens  into  the  cavity  of  the  abdomen  by  the 
fimbriae.  The  Fallopian  tube  is  invested  with  peritoneum,  and  its  canal  is 
lined  with  ciliated  epithelium. 

The  Uterus.  The  uterus,  u,  c,  figure  492,  is  a  somewhat  pyriform 
organ,  and  is  about  7.5  cm.  in  length,  5  cm.  in  breadth  at  its  upper  part 
or  fundus,  but  at  the  neck  or  cervix  only  about  1.25  cm.  The  part  be- 
tween the  fundus  and  neck  is  termed  the  body  of  the  uterus;  it  is  about 
2.5  cm.  in  thickness. 

The  uterus  is  constructed  of  three  principal  layers,  or  coats:  serous, 
fibrous  and  muscular,  and  mucous.  The  serous  coat,  which  has  the  same 
general  structure  as  the  peritoneum,  covers  the  organ  except  the  front  surface 
of  the  neck.  The  middle  coat  is  a  thick  mass  of  unstriped  muscle.  The 
muscle  fibers  become  enormously  developed  during  pregnancy.     The  arteries 


THE    VAGINA  687 

and  veins  are  found  in  large  numbers  in  the  outer  part  so  as  to  form  almost  a 
special  vascular  coat.  The  mucous  membrane  of  the  uterus  is  composed  of  col- 
umnar ciliated  epithelium,  which  extends  also  to  the  interior  of  the  tubular 
glands,  of  which  the  mucous  membrane  is  largely  made  up.  In  the  cervix  of 
the  uterus  the  mucous  membrane  is  arranged  in  permanent  longitudinal  folds, 
palmce  plicatcs.  The  glands  of  this  part  branch  repeatedly,  and  extend  deeplv 
into  the  substance  of  the  cervix.  The  body  has  numerous  simpler  tubular 
glands.  The  glands  are  also  lined  with  ciliated  epithelium.  They  secrete  a 
thick  glairy  mucus,  resembling  white  of  egg. 

The  Vagina.  The  vagina  is  a  membranous  canal  8  to  10  cm.  long, 
extending  obliquely  downward  and  forward  from  the  neck  of  the  uterus, 
which  it  embraces,  to  the  external  organs  of  generation.  It  is  lined  with 
mucous  membrane,  covered  with  stratified  squamous  epithelium,  which  in 
the  ordinary  contracted  state  of  the  canal  is  thrown  into  transverse  folds. 
External  to  the  mucous  membrane,  the  walls  of  the  vagina  are  constructed 
of  unstriped  muscle  and  fibrous  tissue,  within  which  in  the  submucosa, 
especially  around  the  lower  part  of  the  tube,  is  a  layer  of  erectile  tissue.  The 
lower  extremity  of  the  vagina  is  embraced  by  an  orbicular  muscle,  the  sphincter 
vagina;.  The  external  organs  of  generation  are  the  clitoris,  the  labia  interna 
or  nymphes;  and,  the  labia  externa  or  pudenda,  formed  of  the  external  integu- 
ment, and  lined  internally  by  mucous  membrane.  Numerous  mucous  follicles 
are  scattered  beneath  the  mucous  membrane  of  the  external  organs  of  genera- 
tion; and  two  larger  lobulated  glands,  the  glands  of  Bartholin,  analogous  to 
Cowper's  glands  in  the  male,  are  located  at  the  sides  of  the  lower  part  of  the 
vagina.  The  ducts  of  these  glands  are  about  1 2  mm.  long  and  open  immediately 
external  to  the  hymen  at  the  mid-point  of  the  lateral  wall  of  the  vaginal  orifice. 

Ovulation  and  Menstruation.  In  the  process  of  development  in  the 
ovary,  the  individual  Graafian  follicle  increases  in  size  and  graduallv  ap- 
proaches the  surface  of  the  ovary.  When  fully  ripe  or  mature,  it  forms  a 
little  projection  on  the  exterior.  Coincident  with  the  increase  in  size,  which 
is  caused  by  the  augmentation  of  its  liquid  contents,  the  external  envelope 
of  the  distended  vesicle  becomes  very  thin  and  eventually  bursts.  The  ovum 
and  lluid  contents  of  the  vesicle  escape  on  the  exterior  of  the  ovary,  whence 
they  pass  into  the  Fallopian  tube. 

In  man  and  mammals  ovulation  apparently  occurs  only  at  certain  periods. 
These  periods  seem  to  precede  or  occur  during  the  changes  in  the  woman 
that  constitute  the  phenomenon  of  menstruation,  or,  in  the  lower  mammals, 
of  heat. 

That  ovulation  and  discharge  occur  periodically,  and  only  during  the 
phenomenon  of  heat,  in  the  lower  mammalia,  is  made  probable  by  the  facts 
that,  in  all  instances  in  which  Graafian  vesicles  have  been  found  presenting 
the  appearance  of  recent  rupture,  the  animals  were  at  the  time  or  had  recently 
been   in  heat.     There  are  few  authentic  and  detailed  accounts  of  Graafian 


088 


THE    REPRODUCTIVE    ORGANS 


vesicles  being  found  ruptured  in  the  intervals  of  heat;  and  females  do  not  ad- 
mit the  males,  and  never  become  impregnated,  except  at  those  periods.  Al- 
though conception  is  not  confined  to  the  periods  of  menstruation,  yet  it  is 
more  likely  to  occur  about  a  menstrual  epoch  than  at  other  times. 

The  exact  relation  between  the  discharge  of  ova  and  menstruation  is  not 
very  clear.  It  was  formerly  believed  that  menstruation  was  the  result  of 
a  congestion  of  the  uterus  arising  in  association  with  the  enlargement  and 
rupture  of  a  Graafian  follicle;  but  though  a  Graafian  follicle  is,  as  a  rule, 
ruptured  at  each  menstrual  epoch,  yet  instances  are  recorded  in  which  men- 
struation has  occurred  where  no  Graafian  follicle  can  have  been  ruptured,  and 


Fig.  496. 


Fig.  497. 


Fig.  498. 


Fig.  496. — Diagram  of  Uterus  just  Before  Menstruation.  The  shaded  portion  represents  the 
thickened  mucous  membrane. 

Fig.  497. — Diagram  of  Uterus  when  Menstruation  has  just  Ceased,  Showing  the  Cavity  of  the 
Uterus  Deprived  of  Mucous  Membrane. 

Fig.  498. — Diagram  of  Uterus  a  Week  After  the  Menstrual  Flux  has  Ceased.  The  shaded  por- 
tion represents  renewed  mucous  membrane.      (J.  Williams.) 


cases  where  ova  have  been  discharged  in  amenorrheic  women.  It  must 
therefore  be  admitted  that  menstruation  is  not  dependent  on  the  matura- 
tion and  discharge  of  ova. 

Observations  made  after  death,  and  facts  obtained  by  clinical  investiga- 
tion, support  the  view  that  rupture  of  a  Graafian  follicle  does  not  happen  on 
the  same  day  of  the  monthly  period  in  all  women.  In  the  minority  of  cases 
it  may  occur  toward  the  close  or  soon  after  the  cessation  of  a  flow.  On  the 
other  hand,  in  almost  all  subjects  examined  after  death,  of  which  there  is 
record,  rupture  of  the  follicle  appears  to  have  taken  place  before  the  com- 
mencement of  the  menstrual  flow. 


SOURCE    AND    CHARACTER    OF    MENSTRUAL    CHANGES  689 

However,  the  presence  of  the  ovaries  seems  necessary  for  the  performance 
of  the  menstrual  function;  for  women  do  not  menstruate  when  both  ovaries 
have  been  removed  by  operation.  (See  page  432  for  a  discussion  of  the 
functional  effects  of  removal  of  the  ovary.) 

Source  and  Character  of  Menstrual  Changes.  The  menstrual  periods 
usually  occur  at  intervals  of  a  lunar  month,  the  duration  of  each  being  from 
three  to  six  days.  In  some  women  the  intervals  are  so  short  as  three  weeks 
or  even  less;  while  in  others  they  are  longer  than  a  month.  The  periodical 
return  is  usually  attended  by  pains  in  the  loins,  a  sense  of  fatigue  in  the 
lower  limbs,  and  other  symptoms,  which  vary  extremely  in  different  individuals. 

The  menstrual  discharge  is  a  thin  sanguineous  fluid,  and  consists  of  blood, 
epithelium,  and  mucus  from  the  uterus  and  vagina.  The  menstrual  flow  is 
preceded  by  a  general  engorgement  of  all  the  pelvic  organs  with  blood.  The 
cervix  and  vagina  become  darker  in  color  and  softer  in  texture,  and  the  quantity 
of  mucus  secreted  by  the  glands  of  the  cervix  and  body  is  increased.  The 
uterine  mucous  membrane  is  swollen  and  the  glands  are  enlarged.  The  dis- 
charge of  blood,  the  source  of  which  is  the  mucous  membrane  of  the  body 
of  the  uterus,  is  probably  associated  with  uterine  contractions.  There  is 
great  difference  of  opinion  as  to  whether  or  not  any  of  the  uterine  mucous 
membrane  is  normally  shed  during  the  process  of  menstruation.  John 
Williams  believes  that  the  whole  of  the  mucous  membrane  of  the  body  of 
the  uterus  is  thrown  off  at  each  monthly  period,  forming  a  true  decidua  men- 
strualis,  figure  496,  while  Moricke  and  others  believe  that  the  mucous  mem- 
brane remains  intact.  Leopold  believes  that  red  blood-corpuscles  escape 
from  the  congested  capillaries  and  undermine  the  superficial  epithelium,  and 
that  in  this  way  the  superficial  layer  of  the  mucous  membrane  is  eroded  and 
subsequently  regenerated.  There  is  a  period  of  regeneration  followed  by  a 
period  of  rest  before  the  next  repetition.  Minot  distributes  the  variations  in 
time  as  follows : 

Tumefaction 5  days 

Menstrual  discharge 4       " 

Restoration  of  mucosa 7      " 

Period  of  rest 12      " 

The  menstrual  period  is  often  accompanied  by  profound  disturbances  in 
other  parts  of  the  body,  especially  of  the  vascular  and  of  the  nervous  systems 
and  of  the  nutritive  processes. 

Corpus  Luteum.  Immediately  before,  as  well  as  subsequent  to,  the  rupture 
of  a  Graafian  follicle  and  the  escape  of  its  ovum,  changes  ensue  in  the  interior 
of  the  follicle,  which  result  in  the  production  of  a  yellowish  mass,  termed  a 
Corpus  luteum. 

When  fully  formed,  the  corpus  luteum  of  mammals  is  a  roundish  solid 
body,  of  a  yellowish  or  orange  color,  and  composed  of  a  number  of  lobules, 

44 


690  THE    REPRODUCTIVE    ORGANS 

which  surround,  sometimes  a  small  cavity,  but  more  frequently  a  small  stelli- 
form  mass  of  substance,  from  which  delicate  processes  pass  as  septa  between 
the  several  lobules.  The  processes  gradually  change  till  they  nearly  fill  the 
cavity  of  the  follicle,  and  even  protrude  from  the  orifice  in  the  external  cover- 
ing of  the  ovary.  Subsequently  this  orifice  closes,  but  the  fleshy  growth  within 
still  increases  during  the  earlier  period  of  pregnancy,  the  color  of  the  substance 
gradually  changing  to  yellow,  and  its  consistence  becoming  firmer.  After 
the  orifice  of  the  follicle  has  closed,  the  growth  of  the  yellow  substance  con- 
tinues during  the  first  half  of  pregnancy,  till  the  cavity  is  reduced  to  a  com- 
paratively small  size  or  is  obliterated;  in  the  latter  case,  merely  a  white  stelli- 
form  cicatrix  remains  in  the  center  of  the  corpus  luteum. 

The  first  changes  of  the  internal  coat  of  the  Graafian  follicle  in  the  proc- 
ess of  formation  of  a  corpus  luteum  seem  to  occur  in  every  case  in  which  an 
ovum  escapes.  If  the  ovum  is  impregnated,  the  growth  of  the  yellow  sub- 
stance continues  during  nearly  the  whole  period  of  gestation  and  forms  the 
large  corpus  luteum  commonly  described  as  a  characteristic  mark  of  impreg- 
nation. 

The  significance  of  the  corpus  luteum  is  found  in  the  belief  that  it  is  the 
portion  of  the  ovary  especially  concerned  in  the  production  of  an  internal 
secretion  that  affects  the  uterus,  especially  stimulating  it  at  and  before  the 
menstrual  period. 

Menstrual  Life.  The  occurrence  of  a  menstrual  discharge  is  one 
of  the  most  prominent  indications  of  the  commencement  of  puberty  in  the 
female  sex;  though  its  absence  even  for  several  years  is  not  necessarily  at- 
tended with  arrest  of  the  other  characters  of  this  period  of  life  or  incapability 
of  impregnation.  The  average  time  of  its  first  appearance  in  females  of  this 
country  and  others  of  about  the  same  latitude  is  from  fourteen  to  fifteen: 
but  it  is  much  influenced  by  the  kind  of  life  to  which  girls  are  subjected,  being 
accelerated  by  habits  of  luxury  and  indolence,  and  retarded  by  contrary  con- 
ditions. Its  appearance  may  be  slightly  earlier  in  persons  dwelling  in  warm 
climates  than  in  those  inhabiting  colder  latitudes.  The  menstrual  functions 
continue  through  the  whole  fruitful  period  of  a  woman's  life,  and  usually 
cease  between  the  forty-fifth  and  fiftieth  years,  which  time  is  known  as  the 
climacteric.     Menstruation  does  not  usually  occur  in  pregnant  women. 


CHAPTER  XVII 

DEVELOPMENT 

Changes  Which  Occur  in  the  Ovum  Prior  to  Impregnation.     The 

ovum  when  ripe  and  detached  from  the  ovary  is  a  single  cell  enclosed  within 
the  zona  pellucida,  and  containing  the  germinal  vesicle  and  germinal  spot. 
The  ovum  undergoes  a  series  of  changes  preparatory  to  fertilization,  known 
as  maturation,  the  general  effect  of  which  is  to  reduce  the  chromatin  in  anticipa- 


Fig.  499. — The  Maturation  of  theOvum;  Extrusion  of  the  "Polar  Bodies."  (Diagrannu  itic.) 
A,  An  ovum  at  the  commencement  of  the  process;  B,  after  the  formation  of  the  spindle.  The 
chromosomes  are  gathered  at  the  equator  of  the  spindle.  C,  One  apex  of  the  spindle  has  pro- 
jected into  a  bud  on  the  surface,  and  half  of  the  divided  dyads  have  passed  to  each  pole;  D,  the 
separation  of  the  first  polar  body;  E,  the  commencement  of  the  second  polar  body;  F,  the  comple- 
tion of  the  second  polar  body.      (Cunningham.) 


tion  of  the  added  chromatin  from  the  sperm  nucleus.  The  primary  change 
observed  in  the  ovum  consists  in  the  migration  of  the  germinal  vesicle  or  nucleus 
to  the  surface,  and  the  disappearance  of  its  nuclear  membrane,  with  a  con- 
sequent indistinctness  of  its  outline.  Its  protoplasm  becomes  to  a  consider- 
able extent  confounded  with  the  yolk  substance,  and  its  germinal  spot  dis- 
appears.    The  next  step  in  the  process  is  the  appearance  in  the  yolk  of  two 

691 


692 


DEVELOPMENT 


centrosomes  in  a  clear  space  near  the  poles  of  the  elongated  vesicle,  and  the 
formation  of  a  nuclear  spindle,  with  the  aster  at  either  end  lying  near  the  sur- 
face of  the  yolk.     The  nucleus  now  divides 
Ec  into  two  parts,  and  that   nearer  the  surface 

is  extruded  from  the  ovum  enveloped  in  a 
very  small  amount  of  protoplasm.  This 
forms  the  first  polar  body.  The  nucleus 
again  divides  by  mitosis,  one-half  of  the 
chromatin  is  extruded  from  the  ovum, 
forming  a  second  polar  cell;  the  chro- 
matin that  remains  behind  constitutes  the 
female  pronucleus.  The  centrosome  has 
disappeared  and  the  ovum  undergoes  no 
further  changes  unless  fertilized  by  the 
sperm. 

Changes  Following  Impregnation. 
The  process  of  impregnation  of  the  ovum 
has  been  observed  most  accurately  in  the 
lower  types.  The  process  is  as  follows: 
The  head  of  a  single  spermatozoon  joins 
with  an  elevation  of  the  yolk  substance,  the 
tail  remaining  motionless  and  then  disap- 
pearing. The  head  enveloped  in  the  proto- 
plasm then  sinks  into  the  yolk  and  becomes 
a  nucleus,  from  which  the  yolk  substance 
is  arranged  in  radiating  lines.  This  is  the 
male  pronucleus.  The  middle  piece  of  the 
sperm  is  believed  to  furnish  a  new  centro- 
some to  the  ovum.  The  centrosome  now 
divides  and  moves  to  either  side  the  two 
pronuclei,  a  segmentation  spindle  is  formed, 
and  the  egg  undergoes  its  first  segmen- 
tation. 

The  process  of  segmentation  begins 
almost  immediately  in  each  half  of  the  yolk, 
and  cuts  it  also  in  two.  The  process  is 
repeated  until  at  last  by  continued  cleav- 
ages the  whole  yolk  is  changed  into  a  mul- 
berry-like mass,  still  enclosed  by  the  zona 
pellucida,  figure  500.  Fertilization  prob- 
ably takes  place  in  the  Fallopian  tubes,  and 
segmentation  of  the  fertilized  ovum  occurs 
on  its  passage  to  the  uterus. 


Fig.  500. — Conversion  of  the  Mo- 
rula to  the  Blastula.  Formation  of 
Blastodermic  Vesicle  and  Membrane. 
A,  Appearance  of  segmentation  cavity 
and  attachment  of  inner  cell-mass  to 
ectoderm  at  upper  pole  of  ovum;  B1, 
extension  and  flattening  of  inner  cell- 
mass  as  it  oc  urs  in  rabbits  and  some 
other  mammals;  B'2,  extension  of  en- 
toderm as  it  occurs  in  insectivora, 
monkeys,  apes,  and  man;  C,  comple- 
tion of  trilaminar  blastodermic  vesi- 
cle; BC,  blastodermic  cavity;  EC, 
ectoderm;  EE,  embryonic  ectoderm; 
EN,  entoderm;  /,  inner  cell- mass; 
SC,  segmentation  cavity;  ZP,  zona 
pellucida.      (Cunningham.) 


CHANGES     FOLLOWING     IMPREGNATION 


693 


The  passage  of  the  ovum  from  the  ovary  to  the  uterus  occupies  probably 
eight  or  ten  days  in  the  human. 

The  peripheral  cells,  which  are  formed  first,  arrange  themselves  at  the  sur- 
face of  the  yolk  into  a  membrane,  the  ectoderm.  The  deeper  cells  of  the  in- 
terior pass  gradually  toward  the  surface,  thus  increasing  the  thickness  of  the 
membrane  already  formed  by  a  second,  or  entoderm,  layer  of  cells,  while  the 
central  part  of  the  yolk,  the  blastoderm  cavity,  remains  filled  only  with  a  clear 
fluid.  By  this  means  the  yolk  is  shortly  converted  into  a  kind  of  secondary 
vesicle,  the  walls  of  which  are  composed  externally  of  the  original  vitelline 
membrane,  and  within  by  the  newly  formed  cellular  layer,  the  blastoderm  or 
germinal  membrane,  as  it  is  called. 

Important  changes  occur  in  the  structure  of  the  mucous  membrane  of 
the  uterus.  The  epithelium  and  subepithelial  connective  tissue,  together 
with  the  tubular  glands,  increase  rapidly,  and  there  is  a  greatly  increased 
vascularity  of  the  whole  mucous  membrane,  while  a  substance  composed 


Fig.  501. — Section  of  the  Lining  Membrane  of  a  Human  Uterus  at  the  Period  of  Commencing 
Pregnancy,  Showing  the  Arrangement  and  Other  Peculiarities  of  the  Glands,  d,  d,  d,  with  Their 
Orifices,  a,  a,  a,  on  the  Internal  Surface  of  the  Organ.     Twice  the  natural  size. 


chiefly  of  nucleated  cells  fills  up  the  interfollicular  spaces  in  which  the  blood- 
vessels are  contained.  The  effect  of  these  changes  is  an  increased  thickness, 
softness,  and  vascularity  of  the  mucous  membrane,  the  superficial  part  of 
which  itself  forms  the  membrana  decidua. 

The  object  of  this  increased  development  is  the  production  of  nutritive 
materials  for  the  ovum;  for  the  cavity  of  the  uterus  shortly  becomes  filled 
with  secreted  fluid,  consisting  almost  entirely  of  nucleated  cells  in  which  the 
chorion  villi  are  embedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  embedded  in  the  structure 
of  the  decidua,  which  is  yet  quite  soft,  and  in  which  soon  afterward  three 
portions  are  distinguishable.  These  have  been  named  the  decidua  vera,  the 
decidua  basalis,  and  the  decidua  capsularis. 

In  connection  with  these  villous  processes  of  the  chorion,  there  are  de- 
veloped depressions  or  crypts  in  the  decidua  vera,  which  correspond  in  shape 
to  the  villi  they  are  to  lodge;  and  thus  the  chorionic  villi  become  more  or 
less  embedded  in  the  maternal  structures.     These  uterine  crypts,  it  is  im- 


(I!)  1 


DEVELOPMENT 


portant  to  note,  arc  not,  as  was  once  supposed,  merely  the  open  mouths  of 
the  uterine  follicles. 

The  Placenta.  During  these  changes  the  deeper  part  of  the  mucous 
membrane  of  the  uterus,  at  and  near  the  region  where  the  placenta  is 
placed,  becomes  hollowed  out  by  sinuses,  or  cavernous  spaces,  which  com- 
municate on  the  one  hand  with  arteries  and  on  the  other  with  veins  of  the 
uterus.     Into   hese  sinuses  the  villi  of  the  chorion  protrude,  pushing  the  thin 


Unchanged  layer 

Stratum  spongiosum 
Stratum  compactum 

Placental  vil. 


DecWua  basalis 


Maternal  vessel 


Primitive  streak 
Mesoderm 

Placental  villus 


Fig.   so3. 


-Diagram  of  the  Early  Stage  of  Human  Embryo  in  Relation  to  the  Uterus. 
(Cunningham.) 


walls  of  the  sinuses  before  them,  and  so  come  into  intimate  relation  with  the 
blood  contained  in  them.  There  is  no  direct  communication  between  the  blood- 
vessels of  the  mother  and  those  0}  the  fetus;  but  the  layer  or  layers  of  membrane 
intervening  between  the  blood  of  the  one  and  of  the  other  offer  no  obstacle  to 
a  free  interchange  of  matters  between  them  by  diffusion  and  osmosis.  Thus 
the  villi  of  the  chorion,  containing  fetal  blood,  are  bathed  or  soaked  in  maternal 
blood  contained  in  the  uterine  sinuses. 

The  placenta,  therefore,  of  the  human  subject  is  composed  of  a  fetal  part 
and  a  maternal  part — the  term  placenta  properly  including  all  that  entangle- 
ment of  fetal  villi  and  maternal  sinuses,  by  means  of  which  the  blood  of  the 
fetus  is  enriched  and  purified  after  the  fashion  necessary  for  the  proper  growth 
and  development  of  those  parts  which  it  is  designed  to  nourish. 

The  whole  of  this  structure  is  not,  as  might  be  imagined,  thrown  off 
immediately  after  birth.  The  greater  part,  indeed,  comes  away  at  that  time, 
as  the  after  birth;  and  the  separation  of  this  portion  takes  place  by  a  rending 


CIRCULATION    OF     BLOOD     IN    THE     FETUS 


695 


or  crushing  through  of  that  part  at  which  its  cohesion  is  least  strong,  namely, 
where  it  is  most  burrowed  and  undermined  by  the  cavernous  spaces  before 
referred  to.  In  this  way  it  is  cast  off  with  the  fetal  membrane.  The  remain- 
ing portion  is  either  gradually  absorbed,  or  thrown  off  in  the  uterine  dis- 
charges which  occur  at  this  period.  A  new  mucous  membrane  is  of  course 
gradually  developed. 

Circulation  of  Blood  in  the  Fetus.  The  circulation  of  blood  in 
the  fetus  differs  considerably  from  that  of  the  adult. 

Returning  from  the  placenta  by  the  umbilical  vein  the  blood  is  first  con- 
veyed to  the  under  surface  of  the  liver,  where  the  stream  is  divided — a  part  of 
the  blood  passing  straight  on  to  the  inferior  vena  cava  through  a  venous  canal 


Wmll 


Fig.  503. — Diagrammatic  View  of  a  Vertical  Transverse  Section  of  the  Uterus  at  the  Seventh 
or  Eighth  Week  of  Pregnancy,  c,  c,  d ',  Cavity  of  uterus,  which  becomes  the  cavity  of  the  decidua, 
opening  at  c,  c,  the  cornua,  into  the  Fallopian  tubes,  and  at  d  into  the  cavity  of  the  cervix,  which 
is  closed  by  a  plug  of  mucus;  dv,  decidua  vera;  dr,  decidua  reflexa,  with  the  sparser  villi  embedded 
in  its  substance;  ds,  decidua  serotina,  involving  the  more  developed  chorionic  villi  of  the  commenc- 
ing placenta.  The  fetus  is  seen  lying  in  the  amniotic  sac.  The  umbilical  cord  and  its  vessels 
pass  up  from  the  umbilicus  to  the  distribution  of  the  blood-vessels  in  the  villi  of  th  chorion- 
and  the  pedicle  of  the  yolk-sac  the  cavity  between  the  amnion  and  chorion.      (Allen  Thomson.) 


called  the  ductus  venosus,  while  the  remainder  passes  into  the  portal  vein  and 
reaches  the  inferior  vena  cava  only  after  circulating  through  the  liver.  It  is 
carried  by  the  vena  cava  to  the  right  auricle  of  the  heart,  into  which  cavity  the 
blood  is  also  pouring  that  has  circulated  in  the  head  and  neck  and  arms,  and 
has  been  brought  to  the  auricle  by  the  superior  vena  cava.     It  might  be 


696 


DEVELOPMENT 


naturally  expected  that  the  two  streams  of  blood  would  be  mingled  in  the 
right  auricle,  but  such  is  the  case  only  to  a  slight  extent.  The  blood  from  the 
superior  vena  cava — the  less  pure  fluid  of  the  two — passes  almost  exclusively 
into  the  right  ventricle,  through  the  auriculo-ventricular  opening,  just  as  it 
does  in  the  adult.     The  blood  of  the  inferior  vena  cava  is  directed  by  a  fold 


CA   < 


--\ —  -'„-  '-XA-Aorfx 

!    rfZ — i  fulrrC 


-v   A  Vtntru 
\      '     1  Vintm 


*#vt*« 


ffl    \J-mii'    ■"*" 

\\     Ml'®'      ' 


Z  .Hyfwyast. 
\     Arttrt/ 


imm^^ 


Fig.  504. — Diagram  of  the  Fetal  Circulation. 


of  the  lining  membrane  of  the  heart,  called  the  Eustachian  valve,  through  the 
foramen  ovale  into  the  left  auricle  and  into  the  left  ventricle,  and  out  of  this 
into  the  aorta,  and  thence  to  all  the  body,  but  chiefly  to  the  head  and  neck. 
The  blood  of  the  right  ventricle  is  sent  out  in  small  amount  through  the  pul- 
monary artery  to  the  lungs,  and  thence  to  the  left  auricle,  as  in  the  adult, 
but  the  greater  part  by  far  passes  through  a  canal,  the  ductus  arteriosus,  lead- 
ing from  the  pulmonary  artery  into  the  aorta  just  below  the  origin  of  the  three 


PARTURITION 


697 


great  vessels  which  supply  the  upper  parts  of  the  body,  and  is  distributed  to 
the  trunk  and  lower  parts  of  the  body.  A  large  portion  passes  out  by  way 
of  the  two  umbilical  arteries  to  the  placenta.  From  the  placenta  it  is  returned 
by  the  umbilical  vein  to  the  under  surface  of  the  liver,  from  which  the  de- 
scription started. 

After  birth  the  foramen  ovale,  the  ductus  arteriosus,  and  ductus  venosus 
all  close,  and  the  umbilical  vessels  are  tied  off,  so  that  the  two  streams  of  blood 
which  arrive  at  the  right  auricle  by  the  superior  and  inferior  vena  cava,  re- 
spectively, thenceforth  mingle  in  this  cavity  of  the  heart,  and  pass  into  the 


Fig.  505. — Dissection  of  the  Lower  Half  of  the  Female  Mamma  During  the  Period  of  Lactation. 
?. — In  the  left-hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and  partially  un- 
ravelled, and  on  the  right-hand  side  the  glandular  substance  has  been  removed  to  show  the 
reticular  loculi  of  the  connective  tissue  in  which  the  glandular  lobules  are  placed,  i,  Upper  part 
of  the  mammilla  or  nipple;  2,  areola;  3,  subcutaneous  masses  of  fat;  4,  reticular  loculi  of  the  con- 
nective tissue  which  support  the  glandular  substance  and  contain  the  fatty  masses;  5,  one  of 
three  lactiferous  ducts  shown  passing  toward  the  mammilla,  where  they  open;  6,  one  of  the  sinus 
lactei  or  reservoirs;  7,  some  of  the  glandular  lobules  which  have  been  unravelled;  7',  others  massed 
together.      (Luschka.) 


right  ventricle,  by  way  of  the  pulmonary  artery  to  the  lungs,  and  through 
these,  after  aeration,  to  the  left  auricle  and  ventricle,  to  be  distributed  over 
the  body. 

Parturition.  With  the  implantation  of  the  embryo  and  the  devel- 
opment of  the  placenta,  the  uterus  grows  rapidly  until  the  end  of  preg- 
nancy. The  muscles  of  its  walls  increase  enormously  in  volume,  appar- 
ently by  an  increase  in  the  size  of  the  fibers,  and  the  whole  structure  may 
become  thirty  or  forty  times  its  size  in  the  resting  period.  Many  changes 
take  place  also  in  other  parts  of  the  body,  changes  which  are  dependent  on 
the  presence  of  the  fetus.     Full-term  pregnancy  occurs  when  the  uterus  is 


G98 


DEVELOPMENT 


isolated  from  the  nervous  system,  hence  it  has  been  inferred  that  there  is  some 
sort  of  special  secretion,  possibly  of  the  embryo  itself,  that  makes  its  way  into 
the  blood  and  influences  the  organs  of  the  mother. 

At  the  end  of  the  period  of  pregnancy  the  strong  uterine  walls  begin  periodic 
contractions  which  ultimately  result  in  the  delivery  of  the  fetus.  These  con- 
tractions are  at  first  weak  and  at  long  intervals,  but  later  become  very  strong 
and  follow  each  other  in  rapid  succession.  The  uterine  contractions  are  sup- 
ported by  reflex  contractions  of  the  abdominal  and  thoracic  muscles.  After 
the  fetus  is  delivered  the  uterine  contractions  become  milder,  but  still  continue 
until  the  placenta  is  finally  expelled. 

The  initiation  of  the  contractions  of  the  uterus  at  delivery  probably  de- 
pends on  the  chemical  stimulation  of  some  substance  or  substances  produced 
in  the  uterus  itself  or  in  the  fetus;  substances  that  react  on  the  nervous  mech- 
anism and  on  the  uterine  muscles  themselves.  This  view  cannot  be  said  to 
be  proven,  but  it  is  supported  by  certain  observed  facts  and  experiments. 

Lactation.  There  is  a  marked  development  of  the  mammary  glands 
especially  in  the  later  part  of  the  period  of  gestation.  Upon  delivery  of  the 
fetus  the  gland  enlarges  very  sharply  and  an  abundant  secretion  is  formed. 


Fig.  506. 


Fig. 


507. 


Fig.    506. — Section  of  Mammary  Gland  of  Bitch,  Showing  Acini,  Lined  with  Epithelial  Cells  of 
a  Polyhedral  or  Short  Columnar  Form.      X  200.      (V.  D.  Harris.) 
Fig.  507. — Globules  and  Molecules  of  Cow's  Milk.      X  400. 


The  secretion  of  the  first  few  days  is  called  the  colostrum.  It  contains  a 
larger  per  cent  of  solids,  has  the  large  granular  colostral  corpuscles,  is  more 
alkaline  than  ordinary  milk,  and  has  a  specific  gravity  of  1040  to  1046. 

The  mammary  glands  have  been  isolated  from  the  nervous  system  to 
determine  whether  or  not  the  association  in  time  between  their  changes  and 
the  changes  in  the  uterus  were  of  a  nervous  nature.  The  isolated  mammae 
develop  and  begin  lactation  at  parturition  as  in  the  normal.  It  would  seem 
that  here,  too,  there  is  some  special  form  of  stimulation  through  the  medium 
of  the  blood.     Yet  one  must  not  draw  the  conclusion  that  the  nervous  system 


THE    COMPOSITION    OF    MILK  699 

exerts  no  influence  on  the  mammary  gland.  Stimulation  of  the  nerves  to  the 
gland  produces  vascular  changes  that  increase  or  decrease  the  quantity  of 
secretion.  Many  observations  have  been  noted  in  women,  which  show  that 
the  secretion  of  milk  is  sharply  influenced  by,  or  even  completely  suppressed 
by,  nervous  states. 

The  Composition  of  Milk.  Milk  has  a  specific  gravity  of  1028 
to  1034.  Its  fat  is  held  in  emulsion.  Under  the  microscope,  it  is  found  that 
the  milk  globules  vary  in  size,  the  majority  being  from  2  to  3  [±  in  diameter. 
The  old  view  that  they  have  an  investing  membrane  of  albuminous  mate- 
rial is  now  generally  discarded. 

Composition  of  Colostrum  (Pfeiffer). 

Proteids. 5.71 

Fat 2.04 

Sugar 3 .  74 

Salts 0.28 

Water 88.23 

100.00 

Salts  in  Woman's  Milk  (Rotch). 

Calcium   phosphate 23.87 

Calcium  silicate 1.27 

Calcium  sulphate 2.25 

Calcium  carbonate 2.85 

Magnesium  carbonate 3-77 

Potassium  carbonate 23.47 

Potassium  sulphate : 8.33 

Potassium  chloride 12 .05 

Sodium  chloride 21-77 

Iron  oxide  and  alumina °-37 


In  addition  to  the  oil  or  butter  fat,  milk  contains  certain  proteids,  milk- 
sugar,  and  several  salts.  Its  percentage  composition  is  given  in  the  tables 
appended. 

Chemical  Composition  of  Mi-lk.     (After  Foster,  Harrington,  et  al.) 

Water 

Solids 

Fats 

Proteids 

Sugar 

Salts 


Human. 

Cow. 

Mare. 

Bitch. 

87.30 

87 

90 

76 

12.70 

13 

10 

24 





■ 



4.00 

4.0 

2.0 

IO. O 

I.50 

4.0 

2-5 

10. 0 

7.00 

4-3 

5-° 

3-5 

O.20 

0.7 

0.5 

0.5 

INDEX 


Abdominal   viscera,    vascular   nerves 

for,  223 
Abducens  nerve,  554 
Absorption,  361 

conditions  for,  362 

methods  of,  361,  364 

places  for,  362,  370 

rapidity  of,  362,  370 

through  the  intestines,  363 
the  lungs,  370 
the  mouth,  362 
the  skin,  369 
the  stomach,  362 
Accelerator  centers  for  heart,  183 
Accessory  olives,  539 

thyroids,  428 
Accommodation  of  vision,  642,  645 
Achromatic  layer,  1 7 

spindle,  19 
Achromatin,  18 
Achroodextrin,  311 
Acid  albumin,  82 
Acromegaly,  431 
Activating  ferments,  303 
Adamkiewicz  reaction,  196 
Addison's  disease,  429,  431 
Adenoid  tissue,  35 
Adipose  tissue,  37,  38 
Adrenalin,  431 
Adrenals,  428 
After-birth,  694 

-images,  654,  660,  677 

-sensations,  602 
Agglutinative  substances,  129 
Air  cells,  250 

changes  in,  during  respiration,  263 

composition  of,  263 

diffusion  of,  267 

pressure  of,  267,  285 

quantity  breathed,  259,  284 

volume  breathed,  284 
Albumin,  acid,  82 

alkali,  83 


Albumin,  egg,  81 

native,  80,  81 

serum,  81 
Albuminates,  82 

reactions  of,  97 
Albuminoids,  86 

effect  of  diet  of,  411 
Albumins,  81 

reactions  of,  97 
Albumoses,  reactions  of,  97 
Alcohol  as  a  food,  300 
Alkali  albumin,  83 
Ameba,  3 

Ameboid  movement,  3 
Amido-acids,  89 
Amitosis,  10,  19 
Ammonia,  effect  of  breathing,  279 

in  the  urine,  383 
Ammonium  carbamate,  412 
Amylolytic  ferments,  303 
Amylopsin,  303,  334,  337 
Anabolism,  6,  405 
Anabolites,  405 
Anacrotic  limb,  206 

wave,  207,  208 
Anaphase,  20 
Anelectrotonus,  471 
x\nimal  heat,  433 

Animals  differentiated  from  plants,  10 
Anode,  471,  473 
Ano-spinal  center,  526 
Anterior  association  center,  589 
Antipeptone,  336 
Antiperistalsis,  350 
Apnea,  277,  289 
Arborization,  interepithelial,  72 
Archispermiocyte,  679 
Archoplasm,  18 
Areolar  tissue,  34 
Aristotle's  experiment,  669 
Arterial  flow,  196,  198 
rhythmic,  198 
velocity  of,  199 


•01 


702 


INDEX 


Arterial  pulse,  237 

blood-pressure    and  nervous  reg- 
ulation in,  239,  240 
Arteries,  149 

blood-pressure  in,  187 

nerves  of,  151 
Arterioles,  149 
Articulate  sounds,  490 
Asphyxia,  278,  290 
Assimilation,  6 

Association  centers  of  brain,  587 
Aster,  19 

Astigmatism,  649,  674 
Atmosphere,  composition  of,  263 
Attraction  sphere,  18 
Auditory  center,  587 

judgments,  626 

nerve,  556 
Auricles,  action  of,  155 
Auriculo-ventricular     valves,      action 

of,  156 
Autolytic  substances,  129 
Axis  cylinder,  65 
Axone,  64 

Bacteria  in  digestive  tract,  347 

Basement  membrane,  22 

Basket  cells,  562 

Basophile,  113 

Bezold's  ganglia,  175 

Bidder's  ganglia,  175 

Bile,  340,  360 

acids,  341,  360 

capillaries,  340 

coloring  matter  of,  341 

chemical  composition  of,  341 

discharge  of,  343 

functions  of,  342 

mode  of  discharge  of,  343 

mode  of  secretion  of,  343 

pigments  of,  360 

salts,  341,  360 
Bilirubin,  90,  341 
Biliverdin,  90,  341 
Binaural  sensations,  627 
Binocular  vision,  664 
Bioplasm,  2 
Biuret  reaction,  96 
Bladder,  urinary,  377 
Blastema,  2 
Blastoderm,  14 


Blind  spot,  653,  675 
Blood,  10 1 

arterial  flow,  196 
buffy  coat,  103 
capillary  flow,  199 
carbon  dioxide  of,  271 
chemical  composition  of,  115 
circulation  of,  141,  186 
experiments  on,  226 
in  fetus,  695 
coagulation  of,  102,  137 
calcium  in,  106 
conditions  affecting,  106 
fibrin  in,  103 
theories  of,  105 
corpuscles  of,  107 

chemical  composition  of,  139 
'  colorless,  112 

ameboid   movement    of, 

113,  201 
chemical  composition  of, 

117 
number  of,  112 
phagocytosis,  134 
varieties  of,  113 
enumeration  of,  134 
percentage  of,  135 
red,  107 

action  of  reagents  on,  133 
characters  of,  108 
chemical  composition  of, 

118 
development  of,  no 
number  of,  108 
origin  of,  1 10 
varieties  of,  no 
defibrination  of,  104 
differences  between   arterial   and 

venous,  127 
elimination  of  carbon  dioxide  by, 

271 
examination  of,  132 
ferments  in,  117 
flow,  arterial,  196 
capillary,  199 
regulation  of,  209 
velocity  of,  203 

in  arteries,  199 
in  capillaries,  201 
in  veins,  203 
venous,  202 


INDEX 


703 


Blood,  gases  of,  267 
hemoglobin,  118 
isotonicity  of,  136 
laboratory    experiments   on,    132 
laking  of,  128 

microscopical  examination  of,  132 
morphology  of,  107 
oxygen  of,  269 
plasma,  10 1 

chemistry  of,  139 

composition  of,  115 

percentage  of,  135 

reaction  of,  136 
plates,  115 
portal,  127 
pressure,  186 

arterial,  187,  234,  239,  240 

capillary,  195,  238 

in  man,  192 

model,  236 

respiratory    undulations    of, 
191 

variations  in,  195 

venous,  195 
production  of  heat  by  the,  434 
quantity  of,  10 1 

influence  on  secretion,  295 
respiratory  changes  in,  267 
serum,  102 

chemistry  of,  139 

composition  of,  117 

globulicidal  properties  of,  1 2S 
specific  gravity  of,  136 
uses  of,  10 1 

variations  in  composition  of,  126 
velocity  of  flow,  203 
venous  flow,  202 
whipped,  138 
Blushing,  215 

Body,  chemical  composition  of,   78 
energy  requirements  of,  425 
experiments  on  the  chemistry  of, 

95 
Bone,  41 

blood-vessels  of,  42 
canaliculi  of,  43 
cells,  44 

development  of,  45 
growth  of,  50 
Haversian  canals  of,  44 
lacunas  of,  43,  44 


Bone,  lamellae  of,  43,  44 

marrow,  41 

microscopic  structure  of,  43 

ossification  in  cartilage,  46 
in  membrane,  46 

periosteum  of,  42 
Bowman's  sarcous  elements,  60 

theory  of  urinary  secretion,  386 
Brain,  531 

after-,  533 

arrangement    of    different    parts, 

53i 
association  centers  of,  587 
distinctive  characters  of  human, 

532>  574 

fore-,  532 

gray  matter  in,  568 

hind-,  533 

inner-,  532 

mid-,  533 

motor  areas  of,  577,  582 
of  human,  581 
tracts  in,  583 

Rolandic  area  of,  583 

sensory  areas  of,  584 

stem,  531,  532 

vascular  nerve-supply  cf,  220 

weight  of;  574 
Bronchi,  245 
Buffy  coat,  103 
Bulb,  the,  534,  and  see  Medulla 

centers  in,  540 

connections    with    cerebrum   and 
cerebellum,  539 

functions  of,  540 
Bundle  of  Vicq  d'Azyr,  547 
Burdach,  column  of,  514 

Cajal,  cells  of,  570 
Calcification,  47,  50 
Calcium  salts  in  the  body,  94 

in  coagulation  of  the  blood, 
106 

tests  for,  99 
Calorimeter,  290,  426 
Calorimetry,  290 
Canaliculi,  43 
Cane  sugar,  92 
Capillaries,  151 

blood -pressure  in,  195 

structure  of,  152 


704 


INDEX 


Capillary  circulation,  238 
flow,  199 

velocity  of,  201 
Carbohydrates,  91 

absorption  of,  by  intestines,  367 
as  foods,  297,  300 
chemical  reactions  of,  98 
metabolism  of,  416 
Carbon,  amount  excreted,  407 

dioxide,  determination  of,  286,  287 
elimination  of,  263,  264,  271, 
396 
monoxide,  effect  of  breathing,  279 
hemoglobin,  140 
Carbonates,  94 
Carboxyhemoglobin,  121 
Cardiac  action,  force  of,  169 

contractions,  automatic,  231 
experiments  on,  227,  228 
maximal,  174 
cycle,  155,  168 
impulse,  160 
muscle,  61 ,  465,  500 
action  of,  465 

compared     with     other 
muscles,  466,  500 
automatic     contractions     of, 

231 
development  of,  63 
properties  of,  170 
refractory  phase,  465 
nerves,  232 
Cardio-accelerator  centers,  183,  543 
Cardiogram,  161,  226,  228 
Cardiograph,  161 

Cardio-inhibitory  centers,  181,  543 
Cartilage,  38 

development  of,  41 
elastic,  41 
hyaline,  38 
temporary,  40 
white  fibro-,  41 
Casein,  85 
Caseinogen,  85 
Catabolism,  6,  405 
Catabolites,  405 
Catacrotic  limb,  206 

wave,  207 
Catelectrotonus,  471 
Cathode,  471,  473 
Caudate  nucleus,  548 


Cell,  1,  8,  17,  18 

body,  17 

difference  between  plant  and  ani. 
mal,  10 

differentiation,  14,  17 

division  of,  10,  18 

functions  of,  11,  14 

growth,  7,  10 

multiplication,  18 

nucleus  of,  9,  17 

reticulum  of,  8 

structure  of,  8,  17 
Cells,  decay  and  death  of,  22 

derived  elements  of,  22 

modes  of  connection,  21 

origin  of,  21 

shapes  of,  21 

types  of,  21 
Cellulose,  13,  91 
Center  for  muscle  tone,  525 
Centers,  motor,  577,  581 

sensory,  584 

spinal,  526 
Centrosome,  18 

Cerebellar  cortex,  paths  through,  564 
Cerebellum,  561 

connection  with  bulb,  539 

functions  of,  564 

general  structure  of,  562 
Cerebral  cortex,  fibers  from,  572 

structure  of,  568 
Cerebrum,  567 

arrangement  of  parts,  568 

connection  with  bulb,  509 

effects  of  removal  of,  575 

functions  of,  575 

motor  areas  of  cortex,  577,  582 

sensory  areas  of,  584 

weight  of,  574 
Cerumen,  394 
Ceruminous  glands,  394 
Chemical    composition   of    the    body, 

78 
elements  in  the  body,  78 
Chemistry  of  the  body,   experiments 

on,  95 
Chest,  changes  in  diameter  of,  during 

respiration,  284 
Cheyne-Stokes  breathing,  278 
Chlorides  in  the  body,  94 
in  the  urine,  385 


INDEX 


705 


Chlorides,  tests  for,  99 

Chlorine,  effect  of  b/eathing,  279 

Chlorophyll,  12 

Chondrigen,  87 

Chondrin,  87 

Chorda  tympani,  306,  352,  355 

Chordae  tendineae,  148 

Chromatic  aberration,  649,  673 

Chromatin,  18 

Chromophanes,  659 

Chromoplasm,  17 

Chromo-proteids,  84 

Chromosome,  19 

Chyme,  329 

Cilia,  30 

Ciliary  apparatus,  632 

contraction,  468,  502 

epithelium,  502 

motion,  468 
Circulation,  coronary,  183 

during  sleep,  590 

effect  of  respiration  on,  280 

in  brain,  220 

in  erectile  structures,  224 

laboratory  experiments  on,  226 

local  peculiarities  of,  220 

of  blood,  141 

regulation  of  flow,  209 

time  of,  236 

through  blood-vessels,  186 

velocity  of,  203 

vegetable,  4 
Coagulated  proteids,  83 
Coagulating  ferments,  303 
Coagulation  of  blood,  102,  137 

calcium  salts,  in  106 

conditions  affecting,  106,  138 

theories  of,  105 
Cochlea,  619 
Cohnheim's  areas,  61 
Cold,  influence  of  extreme,  436 
Collagen,  86 
Collaterals,  68 
Colloids,  129 
Color,  after-images,  654,  660,  677 

-blindness,  661,  677 

complemental,  ^5o 

extent  of  visual  field  for,  660 

Hering's  theory  of,  663 

limits  of  field  of  vision  for,  677 

-mixing,  677 


Color,  sensations  of,  659,  661 

Young's  and  Helmholtz's  theory 
of,  662 
Colorless  corpuscles,  112 
Colostrum,  608 
Column  of  Burdach,  514 

of  Goll,  514 
Columnar  carneae,  145,  148 
Comma  tract,  516 
Common  sensations,  595 
Complemental  air,  259,  285 
Compound  proteids,  81,  84 
Conductivity  of  muscle,  447 
Conjunctiva,  630 
Connective  tissues,  31 
adenoid,  35 
adipose,  37 
areolar,  34,  36 
cells  of,  31 
development  of,  36 
fibrous,  36 
gelatinous,  34 
general  structure  of,  31 
intercellular  substance  of,  32 
lymphoid,  35 
retiform,  35 
varieties  of,  32 
white  fibrous,  33,  36 
yellow  elastic,  33,  36 
Consonants,  490 
Contractility  of  muscle,  442 
Contraction  phase  of  muscle,  449 
Contracture,  460 
Convoluted  tubule,  372 
Cooking,  effects  of,  301 
Cornea,  631 

Corona  radiata,  545,  546 
Coronary  circulation,  183 
Corpora  cavernosa,  224 
geniculata,  546 
quadrigemina,  546 
striata,  548 
Corpus  Arantii,  148 
dentatum,  562 
luteum,  689 
spongiosum,  224 
Corpuscles,  blood,  107 
Malpighian,  372 
of  Bowman,  372 
of  Golgi,  76 
of  Krause,  74 


706 


INDEX 


Corpuscles  of  Meissner,  74 

of  Pacini,  73 
Coughing,  center  for,  542 
Cranial  nerves,  548 
Crassamentum,  102 
Creatinin,  383,  402,  413,  414 
Crura  cerebri,  545 
Crusta,  545 

petrosa,  52 

phlogistica,  103 
Crystalloids,  129 
Cutis  vera,  393 
Cystin  in  urine,  385 
Cytolysis,  128 
Cytoplasm,  17 

Death,  7 
Decay,  7 
Decidua  basalis,  693 

capsularis,  693 

menstrualis,  689 

vera,  693 
Decussation  of  the  pyramids,  535 
Defecation,  351 

center  for,  526 
Degeneration  in  spinal  cord,  515 

reaction  of,  474 

Wallerian,  506 
Deglutition,  313 

center  for,  316,  542 

nervous  mechanism  of,  315 

time  occupied  in,  315 
Demarcation  currents,  451,  452 
Dendrites,  64 
Dental  papilla,  55 
Dentine,  52 
Depressor  nerve,  215 
Dermis,  393 
Development,  691 
Dextrin,  92 

tests  for,  98 
Dextrose,  92 

tests  for,  98 
Diabetes  mellitus,  418 
Dialysis,  129 
Diapedesis,  201 

Diaphragm  in  respiration,  254,  256 
Diaster,  20 

Diastole  of  heart,  154,  156 
Dicrotic  notch,  207 

pulse,  208 


Dicrotic  wave,  207,  208 

Diet,  normal,  requisites  of,  405,  442 

tables,  423 
Diffusion,  129 
Digestion,  297,  301 

enzymes  in,  301,  303 

experiments  in,  351 

in  intestines,  331,  345,  346 

in  mouth,  303,  353,  354 

in  stomach,  316 
Digestive  ferments,  303 
Diphasic  current,  453 
Diplopia,  550,  664 
Disassimilation,  6 
Distance,  estimation  of,  668 
Diuretics,  action  of,  389 
Dogiel's  cells,  175 
Dreams,  591 
Du  Bois-Reymond's  induction  coil,  445 

key,  444 
Ductless  glands,  influence  on  metabo- 
lism, 427 
Ductus  arteriosus,  696 

venosus,  695 
Dyspnea,  278,  290 

Ear,  cochlea  of,  619 

external,  614 

function  of,  622 

internal,  617 

function  of,  625 

membranous  labyrinth,  618 

middle,  615 

function  of,  622 

organ  of  Corti,  619 

ossicles  of,  616 

tympanum,  615 
Eck's  fistula,  412 
Edestine,  82 
Egg  albumin,  81 
Eggs,  composition  of,  299 
Eighth  nerve,  556 
Elasticity  of  muscle,  442 
Elastin,  87 
Electrodes,  445 
Electrotonus,  471 
Elements,  chemical,  in  body,  78 
Eleventh  nerve,  560 
Emission  of  semen  center,  526 
Emulsification,  99,  337,  342 
Enamel,  53 


INDEX 


707 


Enamel  cap,  56 

germ,  55 

organ,  55 

papilla,  55 
End-brushes,  68 

-bulbs,  74 

-plates,  62 
Endocardiac  pressure,  162 
Endocardium,  143 
Endomysium  59 
Endoneurium,  68 
Endothelium,  24 
Energy,  income  and  output  of,  426 

requirements  for  body,  425 
Enterokinase,  303,  345,  360 
Enzymes,  301 

action  of,  on  pancreatic  juice,  359 

activating,  303 

amylolytic,  303 

classification  of,  302 

coagulating,  303 

digestive,  303 

lipolytic,  303 

proteolytic,  303 
Eosinophile,  100,  113 
Epiblast,  14 
Epidermis,  391 
Epiglottis,  245 
Epinephrin,  431 
Epineurium,  68 
Epithelial  tissues,  22 
Epithelium,  22 

ciliated,  29,  31 

classification  of,  23 

columnar,  23,  24,  28 

cubical,  23 

functions  of,  24,  31 

glandular,  29 

simple,  23 

situations  of,  23,  31 

specialized,  29 

squamous,  23,  27 

stratified,  23,  27 

transitional,  28 
Equilibrium,  sense  of,  628 
Erectile  tissue,  224 
Erection  center,  526 
Erepsin,  303,  345 
Ergograph,  461 
Erythroblasts.  112 
Erythrocytes,  107 


Erythrodextrin,  311 

Eustachian  tube,  615,  624  . 

valve,  143,  696 
Excreta,  analysis  of,  406,  407 

channels  of  elimination  of,  407  ' 

quantity  of,  406 
Excretion,  291,  371,  398 

during  starvation,  422 

from  skin,  395 

laboratory  experiments  in,  398 
Expiration,  forced,  256 

muscles  of,  force  of,  262 

quiet,  256 

relative  time  of,  258 
Expired  air,  carbon  dioxide  of,   263, 
286,  287  , 

changes  in,  263  ; 

External     genitals,     vascular     nerve^ 
for,  224  * 

Eye,  630 

anatomy  of,  630 

astigmatism,  649,  674 

chromatic  aberration  of,  649,  673 

image  formation,  639 

movements  of,  647 

muscles  concerned  in,  647 

optical  apparatus,  638 

axis,  641  ' 

refractive  surfaces  and  media,  639. 

schematic,  641 

spherical  aberration  of,  648,  672 
Eyeball,  630  ( 

blood-vessels  of,  637 

ciliary  apparatus,  632 

cornea,  631 

iris,  632 

lens,  632 

retina,  633 
Eyelids,  630 

Facial  nerve,  554 

function  of,  555 

paralysis  of,  555 

relation  to  taste,  555 

secretory,  555 
Fallopian  tubes,  686 
Falsetto  voice,  489 
Far-point,  672 
Fasciculus  cuneatus,  534 
gracilis,  534 
of  Rolando,  535 


708 


INDEX 


Fasciculus  solitarius,  556  ' 
Fasting,  420,  421 

metabolism  during,  414  .      . 
FatigueM  effect  on  muscular  contrac- 
tion, 497,  498 
Fats,  90,  08  1     ,    , 

absorption  of,  by  intestines,  367 

as  food,  297,  300 

chemical  reactions  of,  98 
.  -digestion  of,  337,  338 

emulsification  of,  99,  337/342. 

energy  value  of,  414  1.1 

metabolism  of ,  4 1 4^       , '       ;  » 

saponification  of,  99',  337'   '    ■ 
i  ,•  -  spurce  of,  in  body,  415      !         .  •  ' ; 
Fatty  acids,  91  \       ,.'    ' 

tests  for,  99  '  ■ 

Feces,  347  ' 

composition  of,  348 

excretion  by,  407 
Fermentation  in  intestine,  34^ 
Ferments,  97    '  .    ' 

!        .chemical  reactions  of;  97 

in  the  blood,  117 

unorganized,    301,    and    see    En- 
, .  C  zym'es  • 

Fetus,  circulation  of  blood' in, '695 
Fibers  of  Remak,  66  • 
Fibrin;  83    :  ' 

ferment,  105      •  .  ' 
Fibrinqgen,  82,  105 
Fictitious  feeding,  321         '..'.'  ' 

Fifth  nerve,  5*5 1 ' 
Fillet,  544     :,.,''•       . 
Filtration,  361  • ,  .'  , 

Finger,  vasomotor  changes  in,  241 
Fish,  composition  of,  299:  t  ' 
Fission,  7  •    •'  '    ■ 

Food,  and  digestion,  297 

effects  of  deprivation  of,  420 

mastication  of,  303 

-principle's,  297  > 

salts  of,  300  : 

Foods,  297/  1 

carbohydrates,  297,'  300  ' 

classification  of,  297 

effect  of  cooking,  301 

fats,  297,  300  ,  ' 

heat  production  from,  426,  437 

income  and  output  of  eriergy,  406 

inorganic,  297/300 


Foods,  liquid,  300 

mineral,  297,  300 

nitrogenous,  297 

percentage  composition  of,  298 

proteids,  297 

salts,  300 

water,  297 
Forced  movements,  567 
Fore-brain,  532 
Form,  estimation  of,  667 
Fossa  ovalis,  143 
Fourth  nerve,  550 
FoVea  centralis,  633 
Frontal  association  center,  589 

Galactose,  93 
Gall-bladder,'  340 
Galvanic  currents,  443 
Ganglia,  508 

spinal,  functions  of,  523 
Gases  in  alimentary  canal,  348 
Gastric  digestion,  316;  355 

changes  in  food  in,  327 
circumstances  influencing, 

327 
cleavage  products  of,  356 
products  of,  326 
time  of,  327 
juice,  321,  355 
acid  of,  323 
action  on  milk,  327 

on  proteids,  326 
artificial,  356 
chemical  composition  of,  323. 

355 
digestive  action  of,  356 
enzyme  action  of,  356 
fictitious    meals,   action    on, 

321 
hydrochloric  acid  in,  324 
pepsin  in,  325 
psychic  secretion  of,  355 
quantity  of,  323 
secretion  of,  320,  355 
secretion,  changes   in  glands  dur- 
ing, 320 
nervous    mechanism    of,  322 
Gelatin,  86 
Gelatinous  tissue,  34 
Gemmation,  7 
Genito-spinal  center,  526 


INDEX 


-tt)9 


Germinal  epithelium,  685 

matter,  9 

spot,  684 

vesicle,  68+ 
Giant  cells,  42 
Glands,  cardiac,  317 

ceruminous,  394 

gastric,  316 

mammary,  698 

pyloric,  318 

reproductive,  relation  to  metabo- 
lism, 432 

salivary,  304 

sebaceous,  395 

secreting,  293 

sudoriferous,  393 

types  of,  293 
Globulin,  serum,  82 
Globulins,  81 

reactions  of,  97 
Globus  pallidus,  548 
Glomerulus.  374 
Glosso-pharyngeal  nerve,  556 
in  respiration,  274    - 
Glottis,  respiratory  movements  of,  257 
Glucoproteids,  85     .  .  , 
Glucose,  92 

Glycin,  341  I 

Glycogen,  92,  417  ; 

destination  of,  418 

formation  of ,  416 

relation  to  metabolism,  416 

sources  of.  417 

tests  for,  98 
Glycogenesis,  416 
Glycoproteids,  85 
Glycosuria,  418 
Goblet  cells,  26 
Golgi,  corpuscles  of,  76 
Goll,  coiumn  of,  514 
Gowers'  tract,  516 
Graafian  follicles,  684 
Granulose,  91 

Haversian  canals,  44 

Head,  vascular  nerve  supply  of,   220 

Hearing,  acuteness  of,  671 

limits  of,  671 

physiology  of,  620    . 
Heart,  142 

action  of,  154 


Heart,  anatomy  of,  142  • 

automaticity  of,  178     '     : 
-beat,  160 

rate  of,  226,  227  ' 

sequence,  .227  1 

theories  of,  174 
-block,  176 
capacity  of,  146 
chambers  of,  143  '< 

character,  of  contraction,  1  70,  174 
coronary  circulation  of,"  183 
cycie  of,  155,  168  ) 

depressor  nerve  of ,  2 1 5  j 

development  of,  146 
endocardiac  pressure,  162       , 
excised,  experiments  on,  228,1229 
force  .of  action,  169  • 

frequency  of  ^action,  154,.'  185 
ganglia  of,  175 

impulse  of,  160  > 

influence,  of  accelerator  nerve  on, 
182,  543         >  < 

of  coronary  circulation  on,  1 83 

of  drugs  on,  185 

of  inhibitor)'  nerves  on,   179, 

543 
of  mechanical  tension  on,  184 
of  nervous  system  on,  179 
of  nutrient  fluids  on,  229 
of  sympathetic     system     on, 

211 
of  temperature  on,  184 
of  vagus  on,  179 

irritability  of,  172 

isolated.,  230  , 

metabolism,  of,  178 

methods  of  investigating  beat  ,1226 

muscle,  61,  500 

properties  of,  170  j  ' 

nerves  of,  179 

production  of  heat  by,  434  • 

regulation  of  force  and  frequency  ! 
of  contraction,  179 

relation  of  rhythm  to  nutrition,  ' 
178 

rhythmic  contraction  of,  1  70.  1  78  : 

size  of,  146    .    > 

sounds  of.  158  ' 

causes  of,  159  . .    ' 

structure  of,  146  '    > 

tonicity  of,  172  ' 


710 


INDEX 


Heart,  valves  of,  148 
action  of,  156 
volume  of,  229 
weight  of,  146 
work  per  diem,  426 
Heat,  animal,  433 

dissipation  of,  434 
from  lungs,  436 
from  skin,  434 
influence  of  extreme,  436 

of  nervous   system   on   pro- 
duction of,  43  S 
produced    in    muscular    contrac- 
tion, 453 
-producing  tissues,  433 
production, of  body-,  425,  433,  437 
regulation  of  body-,  434,  438 

centers  for,  439 
-rigor,  462 

variations  in  loss  of,  434 
in  production  of,  437 
Heidenhain's    experiments    on    urine 

secretion,  386 
Hemachromogen,  124 
Hemacytometer,  135 
Hematin,  124,  125 
Hematoblasts,  1 10 
Hematoidin,  125 
Hematopprphyrin,  124 
Hemianopsia,  585 
Hemin,  125 
Hemiopia,  585 
Hemoglobin,  118,  140,  269 
action  on  gases,  121 
combining  power  with  oxygen,  269 
.     derivatives  of,  124,  14a 
estimation  of,  122,  136 
reduced,  121 
Hemoglobinometer,  122,  136 
Hemolysis,  128 
Hemometer,  136 
Henle's  membrane,  150 

.     loop,  373 
Hepatolytic  sera,  128 
Hind -brain,  533 
Hippuric  acid,  383 

formation  of,  383,  413 
Histons,  84 
Hyaline  cartilage,  38 
cells,  113 
leucocytes,  113 


Hyaloplasm,  8,  1  7 

Hydrochloric  acid,  324,  325 
combined,  324 
digestive  action  of,  325 
test  for  free,  324 

Hydrogen,  amount  excreted,  407 
effect  of  breathing,  279 

Hyperisotonic  solutions,  130 

Hypermetropia,  651 

Hyperpnea,  278,  289 

Hypertonic  solutions,  130 

Hypoblast,  14 

Hypoglossal  nerve,  560 

Hypoisotonic  solutions,  130 

Hypotonic  solutions,  130 

Income  of  energy,  425 

Indol,  360 

Induced  currents,  445 

Induction  coil,  445 

Infundibulum,  144 

Inhibition,  function  of  nerve  centers 

in,  527 
Inogen,  464 
Inorganic  foods,  300 

principles,  93 
Inosite,  93 
Insalivation,  304 
Inspiration,  253 

forced,  256 

muscles  of,  253 
force  of,  262 

quiet,  253 

relative  time  of,  258 
Inspired  air,  263,  286 
Intercellular  substance,  21,  32 
Interepithelial  arborizations,  72 
Internal  capsule,  545 

secretions,  291,  427,  431 
Intestinal  digestion,  331 

role  of  bile  in,  342 

gases,  348 

juices,  344,  360 

secretion,  344 

functions  of,  345 
Intestines,  absorption  in,  363 

action  of  microorganisms  in,  346 

defecation,  351 

digestion  in,  331 

feces  in,  347 

fermentation  in,  347 


INDEX 


711 


Intestines,  gases  in,  348 

large,      summary      of      digestive 
changes  in,  346 

movements  of,  349 

influence  of  nervous  system 
on,  350 

putrefaction  in,  347 

small,      summary      of      digestive 
changes  in,  345 

vascular  nerves  for,  224 
Intonation,  491 
Invertase,  303 
Involuntary  muscle,  501 
Iodothyrin,  428 
Iris,  632 

contraction  of,  647 
Iron,  94 

tests  for,  99 
Irritability,  5 

of  heart-muscle,  172 

of  muscle,  442 
Islands  of  Langerhans,  332 
Isotonic  solutions,  130 
Isotonicity  of  blood,  136 
Ivory,  52 

Judgment  of  form  and  size  of  bodies, 
604 
of  form  and  solidity,  667 
of  size  and  distance,  668 

Jumping,  479 

Karyokinesis,  10,  19 
Karyolymph,  17 
Karyoplasm,  17 
Karyosomes,  18 
Keratin,  87 
Kidneys,  371 

action  of  diuretics  on,  389 

blood  supply  of,  374 

effect  of  blood  pressure  on,  398 

factors   affecting   secretion   from 
386 

function  of,  371 

glomeruli  of ,  374 

Malpighian  bodies  of,  372 

nerves  of,  376,  387 

structure  of,  371 

tubuli  uriniferi  of,  372 

vasa  efferentia  of,  375 
recta  of,  375 


Kidneys,  vascular  nerves  of,  224 

volume  of,  387 
Krause,  corpuscles  of,  74 

membrane  of,  60 
Kronecker-Meltzer    theory   of    deglu- 
tition, 313 
Kymograph,  188 

Labyrinth,  618 

Lachrymal  apparatus,  630 

Lactalbumin,  81 

Lactase,  303 

Lactation,  698 

Lacleals,  364 

Lactic  acid,  test  for,  324 

Lactose,  92 

Lacunae,  43 

Laky  blood,  128 

Langerhans,  islands  of,  332 

Large  intestine,  summary  of  digestive 

changes  in,  346 
Laryngoscope,  485 
Larynx,  245,  480 
Latent  period  of  muscle,  448,  495 
Leaping,  479 

Legumes,  composition  of,  299 
Lens  of  eye,  632 
Lenticular  nucleus,  548 
Leucocytes,  1 1 2 
Leucolytic  sera,  128 
Levers,  action  of,  in  the  body.  475 
Levulose,  93 
Life,  phenomena  of,  1 
Limbs,  vascular  nerves  for,  225 
Linin,  18 
Lipase,  303,  337 
Lipochromes,  90 
Lipolytic  ferments,  303 
Liquid  foods,  300 
Liquor  sanguinis,  10 1 
Lissauer,  tract  of,  516 
Liver,  338 

glycogenic  function  of,  416 

secretions  of,  338 

structure  of,  339 

urea  formation  in,  411 

vascular  nerves  for,  224 
Localization,  cerebral,  577,  584 
Locomotion,  475 
Locus  ceruleus,  544 
Lud wig's  theory  ot  urine  secretion,  386 


712 


INDEX 


Lungs,  248 

absorption  from,  370 

blood  supply  of,  252 

excretion  by,  407 

interchange  of  gases  in,  272 

loss  of  heat  from,  436 

lymphatics  of,  252 

nerves  of,  252 

structure  of,  249 
Luxus  consumption,  409 
Lymph,  131 

chemical  composition  of,  131 

flow,  132 

formation  of,  131 
Lymphatic  sheaths,  perivascular,  154 

spaces,   in  blood-vessels,  154 
Lymphocyte,  100,  113 
Lymphoid  tissue,  35 
Lytic  substances,  128 

Magnesium  salts  in  the  body,  94 
Malpighian  bodies,  372 
Maltase,  303,  311,  334 
Maltose,  92,  312 
Mammary  glands,  698 
Manometer,  188 
Marrow,  bone,  41 
Mastication,  303 

muscles  of,  303  * 
nervous  mechanism  of,  304 
Maximal  stimulus,  454 
Meat,  composition  of,  298 
Meconium,  343 

Medulla  oblongata,  534,  537,  and  see 
Bulb 

as  a  conducting  path,  540 

functions  of,  540 

reflex  centers  of,  540 

section  of,  531 
Medullary  sheath,  65 
Meissner's  corpuscles,  74 
Melanin,  90 
Membrana  decidua,  693 

tympani,  616 
Membranous  labyrinth,  618 
Menstrual  discharge,  689 

life,  690 
Menstruation,  687 
Mesoblast,  14 
Mesothelium,  24 
Metabolism,  6,  405 


Metabolism,  constructive,  6 

destructive,  6 

during  fasting,  414 

endogenous,  410 

exogenous,  410 

influence   of   ductless   glands   on, 
427 
reproductive  glands  on,   432 

intermediate,  410 

nutrition  and  diet,   405 

tissue,  410 
Metaphase,  19 
Metaplasm,  17 
Methemoglobin,  122 
Microcytes,  no 

Micro-organisms,   action   of,  in   intes- 
tines, 346 
Microsomes,  8 
Micturition,  390 

center  for,  526 
Mid-brain,  545 

Milk,  composition  of,  299,  699 
Millon's  reaction,  96 
Mineral  foods,  300,  419 

absorption  of,  in  intestines,  368 
Minimal  stimulus,  454 
Mitosis,  10,  19 
Monaster,  19 
Motor  activities,  coordinated,  475 

areas  of  cortex,  577,  582 
of  human  brain,  581 

end-plates,  62 

impressions,  530 

-oculi  nerve,  549 

tracts  in  human  brain,  583 
Mouth,  absorption  in,  362 

digestion  in,  303 

in  speech,  491 
Movement,  ameboid,  3 

gliding,  4 

streaming,  4 
Movements,  circus,  567 

forced,  567 
Mucigen,  309 
Mucin,  85,  309 
Mucous  membranes,  292 
Mucus  in  urine,  384 
Murexide  test,  402 
Muscle,  blood  supply  of,  62 

cardiac,  61,  465,  500 

chemical  changes  of,  451 


INDEX 


713 


Muscle,  chemical  composition  of,  440, 
441 
clot,  440 

coagulation  of,  440 
conditions  affecting  irritability  of, 

454 

conductivity  of,  447 

contractility  of,  442 

contraction  of,  443,  467 

contracture,  460 

currents,  demonstration  of,  452 

development  of,  62 

effect  of  blood  supply  on,  458 
of  drugs  on,  459 
of  nerve  supply,  458 
of  single  induction  shocks  on, 

446 
of  temperature  on,  456 
of  use  on,  458 

elasticity  of,  442 

electrical  phenomena  of,  451 

end-plates,  62 

experiments  in,  492 

ferments,  441 

heart,  61,  465,  500 

in  rigor  mortis,  461 

involuntary,  57,  466,  501 

compared     with     skeletal    and 
cardiac,  466 

irritability  of,  442,  493 

-nerve  preparation,  492 

nerve  supply  of,  62 

non-striated,  57 

plain,  57 

plasma,  440 

properties  of,  442 

record  of  contraction  of,  443 

serum,  440,  441 

skeletal,  59 

stimuli,  442,  496 

striated,  58 

tetanus,  459 

-tone,  center  of ,  525 

voluntary,  58 
Muscular  action  as  heat  producer,  433 

activity,  464 

center  for  tone  of,  525 

contraction,  443,  465 

action  currents,  452 
apparatus  for  producing  and 
recording,  443 


Muscular  contraction,  changes  in  shape 

during,  449 

characteristics  of  single,  448 

chemical  changes  during,  451 

conditions  affecting  character 

of,  454 
co-ordinated,  460 
differences    between    volun- 
tary and  involuntary,  466 
effect  of  blood  supply  on,  458 
of  drugs  on,  459 
of  fatigue  on,  497,  498 
of  load  on,  499 
of  nerve  supply  on,  458 
of  rate  of  stimulation  on, 

459 
of  repeated  activity  on, 

455 

of-  strength   of   stimulus 
on,  454,  496 

of  temperature  on,   456, 
498,  499 

of  use  on,  458 
electrical  changes  during,  45 1 
energy  liberated  during,  454 
heat  produced  during,  453 
latent  period  of,  448,  495 
metabolism  during,  463 
preparation  for,  446 
record  of,  443,  447 
recording,  446 
refractory  phase  of,  465 
response  to  stimuli  in  volun- 
tary and  involuntary,  466 
simple,  448,  494 
single  twitch,  448 
summation    of    contractions, 

459 
tetanic,  459,  499 
voluntary,  459 
co-ordination,  460,  629 
energy,  464 
tissue,  56 
Musculi  pectinati,  144 
Mydriasis,  550 
Myelin  sheath,  65 
Myelocyte,  100,  113 
Myeloplaxes,  42 
Myoalbumin,  441 
Myoalbumose,  441 
Myoglobulin,  44 . 


714 


INDEX 


Myogram,  448 
Myograph,  pendulum,  448 
Myohematin,  441 
Myopia,  651 
Myosin,  82,  441,  464 

ferment,  441 
Myosinogen,  441,  465 
Myxedema,  428 

Nasal  region,  smell,  610 
Near-point,  645,  672 
Nephrolytic  sera,  128 
Nerve  cells,  70,  503 

arrangement     of,    in     spinal 

cord, 511 
body,  70 
characteristic   of    individual, 

504 
functions  of,  503,  504 
neurone  theory,  504 
nutritive  influence  of,  506 
transmission       of       impulses 

through,  507 
types  of,  508 
centers,  508 

functions  of,  508 
collaterals,  68 
end-brushes,  68 
fibers,  64,  72 

effect  of  battery  current  on, 

471-  473 
fatigue  of,  470 
functions  of,  469 
medullated,  64 
non-medullated,  66 
impulses,  469 

cellulifugal,  507 
cellulipetal,  507 
character  of,  469 
specific  energy  of,  507 
transmission    through    cells, 

5°7 

velocity  of,  470 
stimuli,  442,  469,  492 
terminations,  72 
tissue,  64,  66 
trunks,  67 
Nerves,  cardiac,  232 
cranial,  548 

functions  of,  548 
depressor,  215 


Nerves,  effect  of  currents  on  human, 

47i.  473 
experiments  on,  492 
irritability  of,  492 
spinal,  516 

vasomotor,  211,  213,  217,  219 
Nervous  system,  503 

functions  of,  504 
influence  on  secretion,  295 
sympathetic,  591 
tissues,  64,  66 

axones  of,  64,  507 
dendrites  of,  64,  507 
ganglia  of,  508 
neuroglia  of,  64,  77 
Pacinian  corpuscles,  73 
Neuraxone,  64 
Neurilemma,  64 
Neuroglia,  64,  77 
Neurokeratin,  87 
Neurone,  64,  503 
theory,  504 
varieties,  508 
Neutrophile,  100,  113 
Ninth  nerve,  556 
Nitrogen  in  proteids,  88 
Nitrogenous  bodies,  79 
equilibrium,  408 
foods,  297 
output,  409 
Nitrous  oxide,  effect  of  breathing,  279 
Nodes  of  Ranvier,  65 
Nceud  vital,  272 

Nostrils,  respiratory  movements  of,  257 
Nuclear  matrix,  17 
Nuclei  of  optic  thalamus,  546 
Nucleic  acid,  85 
Nucleins,  85 
Nucleoli,  18 
Nucleoplasm,  17 
Nucleoproteids,  84,  85 
Nucleus,  9,  17 

ambiguus,  556 
ruber,  546 
structure  of,  1 7 

Obesity,  416 
Ocular  fixation,  664 
Odontoblasts,  52,  55 
Oils,  90 

as  food,  300 


INDEX 


715 


Olein,  90 

Olfactory  apparatuo,  609 

bulb,  611 

center,  585 

glomeruli,  586 

membrane,  613 

nerve,  586 

tract,  587 
Olivary  bodies,  536,  538 
Olive,  accessory,  539 

superior,  544 
Onkograph,  388 
Onkometer,  388 
Ophthalmoscope,  655 
Optic  center,  585 

nerve,  633 

thalami,  546 
Optical  apparatus,  638 
defects  in,  648 
Organ  of  Corti,  619 
Organized  ferments,  346 
Osmosis,  129 
Osmotic  pressure,  130 
Ossein,  86 

Osseous  labyrinth,  618 
Ossicles  of  ear,  616 
Ossification,  45 

center  of,  46 

in  cartilage,  46 

in  membrane,  46 
Osteoblasts,  46 
Osteoclasts,  48 
Osteogenetic  fibers,  46 
Output  of  energy,  426 
Ovaries,  683 

relation  to  metabolism,  432 
Oviducts,  686 
Ovulation,  687 
Ovum,  684,  686 

changes    in,   following   impregna- 
tion, 692 
prior  to  impregnation,  691 
Oxalic  acid  in  urine,  385 
Oxygen,  amount  excreted,  407 
in  expired  air,  265 
in  tissues,  270 

determination  of,  in  air,  286 
Oxyphile,  113 

Pacinian  corpuscles,  73 
Pain,  sense  of,  602 


Pancreas,  332 

enzymes  of,  334 
extirpation  of,  431 
extract  of,  334 
internal  secretion  of,  431 
islands  of  Langerhans  in,  332 
secretion  of,  333 
structure  of,  332 
Pancreatic  digestion,  358 

cleavage  products  of,  359 
fistula,  333 
juice,  333,  358 

artificial,  358 

chemical  characters  of,  358 

composition  of,  334 
conditions  influencing  action 

of,  338 
enzymes  of,  334,  358 

action  of,  335,  338,  359 
secretion  of,  358 

action  of  nerves  on,  334 
action    of     secretin    on, 

334,  358 
Papilla?  of  skin,  392 

of  tongue,  606 
Paralytic  secretion  of  saliva,  306 
Paranucleoproteids,  84 
Parathyroid  glands,  428 
Parietal  association  center,  589 
Parotid  gland,  304 

nerves  of,  308 
Parturition,  697 

center,  527 
Pelvic  viscera,  vascular  nerves  for,  224 
Penis,  681 
Pepsin,  303 

action  of,  325 

in  gastric  juice,  325 
Pepsinogen,  325 
Peptone  plasma,  107 
Peptones,  84,  325 

characteristics  of,  326 

reactions  of,  97 
Perforating  fibers  of  Sharpey,  45 
Pericardium,  142 
Perichondrium,  38,  46 
Perimysium,  59 
Perineurium,  68 
Periosteum,  42 

Peripheral  resistance,  186,  210 
Peristalsis,  intestinal,  349 


716 


INDEX 


Peristalsis,  reversed,  350 
Perivascular  lymphatic  sheaths,  154 
Perspiration,  395 
Pfliiger's  law  of  contractions,  472 
Phagocytes,  134 
Phagocytosis,  134 
Phakoscope  of  Helmholtz,  674 
Phenomena  of  life,  1 
Phenomenon  of  treppe,  497 
Phosphates,  94 

tests  for,  99 
Phosphoric  acid  in  urine,  384 
Phosphorus  in  foods,  420 
Phrenic   nerve,    influence   on   respira- 
tion, 289 
Physiological  material,  source  of,  1 5 

utilization  of,  15 
Physiology,  1 
Pigment  cells,  32 
Pigments,  90 

bile,  360 
Pituitary  body,  431 
Placenta,  694 

Plants  differentiated  from  animals,  16 
Plasma,  10 1,  115 

chemistry  of,  139 

composition  of,  115 

percentage  of,  in  blood,  135 

reaction  of,  136 
Plasmosomes,  18 
Plethysmogram,  241 
Pleura?,  248 
Pneumogastric    nerve,    558,    and    see 

Vagus 
Pneumograph,  258 
Pons  Varolii,  543 
Postdicrotic  wave,  207 
Posterior  longitudinal  bundle,   544 

marginal  zone,  516 

pyramids,  534 

roots  of  spinal  nerves,  518,  523 
Potassium  salts  in  the  body,  94 
Poultry,  composition  of,  299 
Precipitins,  129 
Predicrotic  wave,  207 
Presbyopia,  651 
Pressor  nerves,  216 
Pressure,  endocardiac,  162 
Prickle  cells,  27 
Pronucleus,  female,  692 

male,  692 


Prophase,  19 
Prostate  gland,  682 
Protamin,  84,  89 
Proteids,  79 

absorption  of,  from  intestines,  365 

action  of  trypsin  on,  336 

as  fat  formers,  410 

as  glycogen  formers,  410 

circulating,  409 

coagulated,  83,  97 

color  reactions  of,  96 

compound,  81,  84 

classes  of,  80 

decomposition  products,  87 

digestion  of,  325 

floating,  409 

metabolism  of,  408,  409 

morphotic,  409 

nitrogen  in,  88 

precipitations,  96 

properties  of,  79 

reactions  of,  95 

simple,  80,  81 

sulphur  in,  89 

tissue,  409 
Proteolytic  ferments,  303 
Proteoses,  84,  325 
Prothrombin,  106 
Protoplasm,  1,  2 

chemistry  of,  3 

definition  of,  2 

effect  of  stimuli  on,  5 

growth  of,  7 

irritability  of,  5 

movement  of,  3 

physiological  characteristics  of,  3 

properties  of,  2 

reproduction  of,  7 

structure  of,  8 
Pseudo-nucleoproteids,  84 
Ptosis,  550 
Ptyalin,  303,  310 

action  of,  303,  311,  354 
Pulse,  204 

arterial,  237 

dicrotic,  208 

variations  in  rate  of,  185 

-wave,  rate  of  propagation  of,  237 
Pulvinar,  547 
Pupil,  632 

contraction  of,  647 


INDEX 


717 


Pupil,  dilatation  of,  647 
center  for,  542 

reflexes,  647 
Purkinje's  cells,  562 

figures,  653 

shadows,  676 
Purkinje-Sanson's  images,  673 
Putamen,  548 

Putrefaction  in  intestines,  347 
Pyramids,  534 

decussation  of,  535 

Racemose  glands,  294 
Ranvier,  nodes  of,  65 
Reaction  of  degeneration,  474 
Red  corpuscles,  107 

action  of  reagents  on,  133 
chemical  composition  of,  118 
development  of,  no 
origin  of,  no 
varieties  of,  1 10 

nucleus,  546 
Reflex  action,  519 

time  of,  523 

arc,  519 

centers  in  medulla,  540 
Reflexes,  complex,  521 

cutaneous,  528 

inhibition  of,  527 

morbid,  527 

muscle,  528 

simple,  520 

special  centers  for,  5  26 

spinal,  524 

tendon,  528 
Refraction,  671 
Refractory  period,  172 

phase,  465 
Relaxation  phase  of  muscle,  449 
Remak's  fibers,  66 

ganglia,  175 
Rennin,  303,  334 

action  of,  327,  337,  357 
Pveproductive  organs,  679 

of  female,  683 

of  male,  679 
Reserve  air,  260,  285 
Residual  air.  260 
Respiration,  243 

changes    in    diameter    of    chest, 
during,  284 


Respiration,  effect  of  altitude  on,  280 
of,  on  circulation,  280 
of  various  gases  on,  279 
of  vitiated  air  on,  279 

expiration,  256 

influence  of  cutaneous  nerves  on, 
288 
of  general  sensory  nerves  on, 

274,  288 
of  glosso-pharyngeal  on,  274 
of  phrenic  on,  289 
of  superior  laryngeal  on,  274 
of  vagus  on,  273,  289 

inspiration,  253 

internal,  244 

laboratory  experiments  in,  283 

mechanism  of,  253 

nervous  apparatus  of,  272,  288 

rhythm  of,  258 

special  types  of,  277 

tissue,  244 

volume  of  air  breathed,  284 
Respirations,  number  of,  262,  283 
Respiratory  apparatus,  244 

elimination  of  carbon  diox- 
ide by,  271 
nervous  regulation  of,  272 

capacity,  260,  285 

circumstances  affecting,   261 

center,  272,  542 

automatic  action  of,   275 
stimulation  of,  275 

changes  in  air  breathed,  263 
in  the  blood,  267 
in  the  tissues,  270 

interchange,  290 

movements,  253 

character  of,  283 
establishment    of,    at    birth, 

277 
nervous  mechanism  of,    288 
rate  and  character  of,  287 
recording  of,  257,  283 
relative  time  of,  258 
of  nostrils  and  glottis,  257 

murmur,  259 

muscles,  force  of,  262 

pressure,  267,  285 

quotient,  266 

rate,  262,  283 

rhythm,  258 


718 


INDEX 


Respiratory  rhythm,  action  of  stimuli 
on,  273 
terms  for  quantity  of  air  breathed, 

259 
Rete  mucosum,  392 
Reticular   formation  in  medulla,   538 
Reticulum,  8,  17 
Retiform  tissue,  35 
Retina,  633 

cones  of,  636 

inverted  image  on,   672 

layers  of,  634 

localization  in,  657 

movement  of  pigment  cells,  659 

rods  of,  636 
Retinal  image,  duration  of,  676 

relation  of  size  to  distance, 
676 
Retinoscopy,  678 
Rheoscopic  frog,  470 
Rhodopsin,  658 
Rhythmical  contractility,  170 
Rhythmicity  of  arterial  flow,  198 
Ribs,    movement    of,    in    respiration, 

255 
Rigor  mortis,  461 

cause  of,  461- 

heat,  462 

order  of  occurrence,  462 

water,  462 
Rima  glottidis,  245 
Rolandic  area,  583 
Running,  479 

Saccharose,  92 
Sacculus,  618,  629 
Saliva,  309 

action  of ,  on  starch,  311,  312,  353 
chemical  composition  of,  310,  352 
function  of,  310 
properties  of,  310 
ptyalin  in,  303,  310,  311 
quantity  of,  310 
secretion  of,  center  for,  305 
mechanism  of,  305 
rate  of,  310 
Salivary  digestion  in  stomach,  313 

influence  of  acids  and  alkalies 
on,  354 
of  temperature  on,   353 
glands,  304 


Salivary  glands,    changes    in,   during 
secretion,  308,  352 
nerves  of,  351 
structure  of,  304 
secretion,  308 
reflex,  351 
Salts,  absorption  of,  by  intestines,  368 
as  foods,  300 
bile,  341,  360 
in  the  body,  93 
tests  for,  99 
Sanson's  images,  644 
Saponification,  99,  337 
Sarcode,  2 
Sarcolemma,  59 
Sarcoplasm,  61 
Sarcostyles,  59 

Sarcous  elements  of  Bowman,  60 
Scheiner's  experiment,   673 
Schwann,  sheath  of,  65 
Sebaceous  glands,  394 
Secretin,  334,  345 

influence  on  pancreatic  secretion, 

334.  358 
Secreting  glands,  2  93 

production  of  heat  by,  434 
types  of,  293 

organs,  types  of,  292 
Secretion,  291 

circumstances  influencing,   295 

discharge  of,  295 

external,  291 

internal,  291,  427,  431 

organs  and  tissues  of,  292 

process  of,  294 

psychic,  355 

true,  291 
Segmentation,  692 
Semicircular  canals,  619,  628 
Semilunar  valves,  148 
action  of,  157 
Seminal  fluid,  682 
Sensations,  binaural,  627 

common,  595 

objective,  596 

of  color,  659 

special,  596 

subjective,  596 
Sense,  hearing,  614 

muscular,  595,  603 

of  equilibrium,  628 


INDEX 


719 


Sense  of  pain,  602 

of  sight,  630 

of  smell,  609 

of  taste,  604 

of  temperature,  600 

of  touch,  597 

organs,  directions  for  experiments 
on,  669 

perceptions,  597 
Senses,  the  595 

special,  597 
Sensorium,  596 
Sensory  areas  of  brain,  584 

illusions,  596 

impressions,  529 
Serous  membranes,  292 
Serum,  102 

agglutinative  substances,  129 

albumin,  81 

blood,  102,  117 

chemistry  of,  139 

composition  of,  117 

globulicidal  action  of,  128 

globulin,  82 

hemolytic  action  of,  128 

precipitins  of,  129 
Seventh  nerve,  554 
Sharpey's  fibers,  45 
Sight,  630 
Silicon,  94 
Sixth  nerve,  554 
Size,  estimation  of,  668 
Skein,  19 
Skin,  absorption  from,  369 

amount    of    carbon    dioxide    ex- 
haled by,  396 

excretion  by,  407 

excretory  functions  of,  391,  395 

exhalation  from,  396 

functions  of,  391,  397 

glands  of,  393 

loss  of  heat  from,  434 

papillae  of,  392 

respiratory  functions  of,  396 

structure  of,  391 
Sleep,  590 
Small  intestine,  digestion  in,  345 

mucosa  of,  364 

villi  of,  364 
Smell,  center  for,  585 

sensation  of,  670 


Smell,  sense  of,  609 

Soaps,  91 

Sodium  salts  in  the  body,  94 

Solidity,  judgment  of,  667 

Somesthetic  area  of  brain,  584 

Somnambulism,  591 

Sound,  622 

Sounds,  articulate,  488,  490 

localization  of,  626 

of  the  heart,  158 

pitch  of,  625 
Special  centers  in  bulb,  540 

sensations,  596 
Speech,  480,  490 

action  of  tongue  in,  491 

mouth  in,  491 
Spermatids,  679 
Spermatocytes,  679 
Spermatogonia,  679 
Spermatozoa,  679,  680,  682 
Spermin,  432 

Spherical  aberration,  648,  672 
Sphygmogram,  206 
Sphygmograph,  205 
Sphygmomanometer,  194 
Sphygmometer,  206 
Spinal  accessory  nerve,  560 

bulb,  534 

centers,  525,  526 

cord,  510 

antero-lateral  ascending  tract, 

descending  tract,   516 
arrangement  of  nerve  cells  in, 

ascending    degeneration    of, 

columns  of,  514 

comma  tract  of,  516 

conduction  in,  528 

course  of  motor  impulses  in, 

53° 
of   sensory  impulses  in, 

529 
crossed  pyramidal  tract,  515 
descending   degeneration   of, 

5i5 
direct  cerebellar  tract,  516 

pyramidal  tract,  515 
functions  of,  510,  513 
Gowers'  tract,  516 


720 


INDEX 


Spinal  cord,  hemisection  of,  531 
intrinsic  cells  in,  513 
irradiation    of    impulses    in, 

521 
Lissauer's  tract,  516 
peculiarities  of  different   re- 
gions, 519 
postero-lateral  column,  516 
postero-marginal  zone,  516 
postero-median  column,   516 
reflex  action  in,  519,  524 
reticular  formation,  513 
tracts  of ,  5 1 4 
weight  of,  574 
nerve-roots,  functions  of,  523 
nerves,  516 

anterior  roots,   517,   523 
course  of  fibers,  517 
posterior  roots,  518,  523 
reflexes,  524 
Spirem,  19 

Spleen,  vascular  nerves  for,  224* 
Spongioplasm,  8,  17 
Staircase  contractions,  455 
Stammering,  491 
Starch,  91 

action  of  amylopsin  on,  337 

of  ptyalin  on,  311,  312,   353 
chemical  reactions  of,  98 
hydrolysis  of,  98 
Starvation,  420 

death  from,  420 

effect  on  body  temperature,  421 
symptoms  of,  420,  421 
Steapsin,  303,  334,  337 
Stercobilin,  90,  342 
Stereoscope,  667 
Stethograph,  258 
Stethometer,  257 
Stimuli,  forms  of,  442 
maximal,  454 
minimal,  454 
Stokes'  fluid,  121 
Stomach,  316 

absorption  from,  362 
action  of  pylorus,  328 
blood-vessels  of,  319 
changes   in  glands   during   secre- 
tion, 320 
digestion  in,  313,  316 
gases  in,  349 


Stomach,  glands  of,  316 
lymphatics  of,  319 
movements  of,  327 
nerves  of,  316 
nervous  control  of  movements  of, 

329 
secretion  in,  320 
structure  of,  316 
vascular  nerves  for,  224 
Stomata,  25 
Strabismus,  550 
Stratum  granulosum,  392 
lucidum,  392 
Malpighii,  392 
Striated  muscle,  58 

development  of,  62 
Submaxillary   gland,    action   of   atro- 
pine on,  306 
paralytic  secretion  of,  306 
secretion  of,  306 
Substantia  nigra,  545,  546 
Succus  entericus,  344 
Sucking,  center  for,  542 
Sudoriferous  glands,  393 
Sugar,  test  for,  in  urine,  403 
Sulphates,  94 

tests  for,  94 
Sulphur  in  proteids,  89 
Sulphuretted      hydrogen,      effect      of 

breathing,  279 
Sulphuric  acid  in  urine,  384 
Sulphurous  acid,  effect  of  breathing, 

279 
Summation,  459 

of  stimuli,  521 
Superior    laryngeal    nerve  in  respira- 
tion, 274 
Supplemental  air,  260 
Suprarenal  capsules,  428 

active   principle  of,   430 
functions  of,  428 
internal  secretion,  431 
nerves  of,  428 

relation     to     Addison's    dis- 
ease, 429,  431 
extract,  430 
Swallowing,  313 
Sweat,  395 

centers,  543 

chemical  composition  of,  395 

glands,  393 


INDEX 


r^i 


Sweat,    influence   of   nervous   system 

on  secretion  of,  397,  399 
Sympathetic    ganglia,    functions    and 
structure,  591,  594 
nervous  system,  591 
functions,  594 

organization     and     distribu- 
tion, 591 
Synapsis,  520 
Synovial  membranes,  292 
Systole  of  heart,  154,  156 

Tactile  corpuscles,  74,  599 
of  Meissner,  74 

menisques,  75 
Taste,  604 

after-,  608 

buds,  605 

center,  587 

influence     of     fifth     nerve     on, 

553 
seat  of,  604,  607 
sensation  of,  670 
varieties  of,  607 
Taurin.  341 
Teeth,  50 

dentine  of,  52 
development  of,  54 
enamel  of,  53 
ivory  of,  52 
permanent,  51 
structure  of,  51 
temporary,  50 
Tegmentum,  544,  545,  546 
Telophase,  20 
Temperature,  body,  433 

dissipation  of,  435 

influence  of  extreme  heat  and 

cold  on,  436 
regulation  of,  434 
sense  of,  600,  669 
variations  in,  433 
influence    of,    on    muscular    con- 
traction, 456 
Tenth  nerve,  558 
Testes,  679 

relation  to  metabolism,  432 
Tetanometer,  499 
Tetanus,  459,  499 
Thermogenic  centers,  439 
Third  nerve,  549 

46 


Thoracic  viscera,  vascular  nerves  for, 

222 
Thorax,  respiratory  changes  in  diam- 
eter, 284 
Thrombin,  105 
Thrombocytes,  115 
Thrombogen,  106 
Thrombokinase,  106,  139 
Thyroid  gland,  427 

accessory,  428 
functions  of,  428 
Tidal  air,  259,  285 
Tissues,  connective,  31 

elementary,  22 

epithelial,  22 

interchange  of  gases  in,  272 

muscular,  56 

nervous,  64 
Tone,  of  artery,  212 

of  muscle,  172,  525 
Tongue,  604 

action  of,  in  speech,  491 

papillae  of,  606 
Tonicity  of  heart  muscle,  172 
Tooth-pulp,  51 
Touch  corpuscles,  599 

sense  of,  597,  669 

acuteness  of,  599 
Tract  of  Gowers,  516 

of  Lissauer,  516 
Traube-Hering  curves,  216 
Treppe,  phenomenon  of,  497 
Trigeminus  nerve,  551 

functions  of,  552 
Triolein,  90 
Tripalmitin,  90 
Tristearin,  90 
Trochlearis  nerve,  55c 
Trommer's  test,  403 
Trunk,  vascular  nerves  for,  225 
Trypsin,  303,  335 

action  of,  336 
Tubular  glands,  293 
Tubuli  seminiferi,  679 

uriniferi,  372 
Twelfth  nerve,  560 
Tympanum,  615 

Unorganized  ferments,  301,  and  see 

Enzymes 
Unstriped  muscle.  57 


722 


INDEX 


Urea,  380 

amount  in  tissues  of  body,  381 

antecedents  of,  412 

determination  of,  402 

formation  of,  381,  411 

preparation  of,  401 

properties  of,  380 

quantity  excreted,  382 
Ureters,  377 
Uric  acid,  382,  402 

condition  of,  in  urine,  382 

formation  of,  413 

properties  of,  382 

tests  for,  402 
Urinary  bladder,  377 
Urine,  377 

abnormal  constituents  of,  403 

albumin  in,  385,  403 

ammonia  in,  383 

analysis  of,  399 

average    daily    quantity   of   con- 
stituents, 379 

chlorides  in,  385,  400 

creatinin  in,  383,  402 

cystin  in,  385 

dextrose  in,  385,  403,  404 

discharge  of,  390 

diuretics,  action  of,  389 

excretion  by,  407 

of,  experiments  on,  386 

factors  affecting  secretion  of,  386 

filtration  theory  of  secretion,  386 

general  properties  of,  377 

hippuric  acid  in,  383,  413 

method  of  excretion  of,  386 

mucus  in,  384 

nitrogenous  substances  in,  380 

occasional  constituents  of,  385 

oxalic  acid  in,  385 

phosphates  in,  384,  401 

pigments  in,  383,  402 

quantity  of,  377,  399 

reaction  of,  378,  399 

/elation  of  blood  pressure  to  secre- 
tion of,  398 

saline  matter  in,  384 

secretion  of,  theories  of,  386 

solids  of,  400 

specific  gravity  of,  379,  399 

sugar  in,  403,  404 

sulphates  in,  384,  400 


Urine,  urea  in,  380,  401 

uric  acid  in,  382,  402 

variations    in    quantity    of    con- 
stituents, 379 
in  specific  gravity,  379 
Uriniferous  tubules,  372 
Urobilin,  90,  342,  383,  402 
Urochrome,  90,  383 
Uroerythrin,  90,  384 
Uromelanin,  384 
Uterus,  686 
Utriculus,  618,  629 

Vagina,  687 
Vagus  nerve,  558 

effects  of  section,  560 

functions  of,  560 

relation  to  deglutition,  315 
to  gastric  secretion,  321 
to  heart's  action,  179 
to  respiration,  273,  289 
Valves  of  heart,  148 

action  of,  156 

of  veins,  154 
Vas  deferens,  680 
Vasoconstrictor  activity,  219 

center,  214 

nerves,  213,  219,  226 

reflexes,  215 
Vasodilator  activity,  219 

center,  218 

nerves,  217,  219 

reflexes,  218 
Vasomotor  centers,  543 

changes,  241 

nerves,  211,  220 

tone,  214 
Veins,  152 

blood  pressure  in,  195 

structure  of,  152 

valves  of,  154 

vasoconstrictor  nerves  in,  226 
Venous  flow,  202 

velocity  of,  203 
Ventilation,  279 

Ventricles  of  heart,  action  of,  155 
Vesico-spinal  center,  526 
Vesiculae  seminales,  680 
Vesicular  breathing,  259 
Vicq  d'Azyr,  bundle  of,  547 
Villi,  36: 


INDEX 


723 


Visceral  sensations,  529 

Vision,  accommodation  of,  642,  645 

binocular,  664 

field  of,  657 

limits  of,  660,  672,  677 

localization  of,  657 

mechanism     of     accommodation, 

645 
range  of  distinct,  645 
Visual  acuity,  678 
center,  585 
judgments,  667 
purple,  658 
sensations,  652 

after-images,  654 
intensity  of,  654 
sense,  630 
Vital  capacity,  260,  285 

phenomena,  1 
Vitellin,  86 

Vitiated  air,  effects  of,  279 
Vocal  cords,  245,  480 

movements  of,  486 
Voice,  480 

difference  between  male  and   fe- 
male, 488,  489 
in  singing  and  speaking,  488 
production  of,  479 
quality  of,  489 


Voice,  vocal  range  of,  488 
Vomiting,  330 

action  of  abdominal  muscles,  330 
of  diaphragm,  330 
of  pylorus,  330 
center  for,  331 
nervous  mechanism  of,  331 
Vowels,  490 

Walking,  475 

Wallerian  degeneration,  506,  515 

Water,  95 

absorption  of,  in  intestines,  368 
amount  excreted,   396,   407 
in  expired  air,  266 
in  the  body,  95 
as  food,  300 
rigor,  462 
Weyl's  reaction,  402 
White  fibrous  tissue,  ^^ 

development  of,  36 
Wreath,  19 

Xantho-proteic  reaction,  96 

Yellow  elastic  tissue,  33 

development  of,  36 

Zymogens,  302 


QF34 
Kirkes 


1907 


